Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery including a positive electrode plate, a negative electrode plate, an electrode assembly in which a separator interposed between the positive electrode plate and the negative electrode plate is wound in one direction, a battery can in which the electrode assembly is housed, an electrolyte injected into the battery can, and a sealing body for sealing an open end portion of the battery can. The positive electrode plate and the negative electrode plate each include a plain portion where an active material layer is not formed, and at least a part of the plain portion of the positive electrode plate or the negative electrode plate defines an electrode tab. The occupied volume of the electrolyte is 101% by volume or more and 119% by volume or less with respect to the total pore volume of the positive electrode plate, the negative electrode plate, and the separator.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0183661 filed on December 23, 2022 and Korean Patent Application No. 10-2022-0183669 filed on December 23, 2022, and all the contents disclosed in the documents of the Korean patent applications are incorporated herein by reference in their entirety.

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

Background Art

[0003] As technologies such as electric vehicles and portable electronic devices have developed, the demand for lithium secondary batteries as an energy source has been rapidly increasing.

[0004] Lithium secondary batteries are classified into cylindrical, prismatic, and pouch-type batteries according to the form of the battery case. Among them, cylindrical batteries are manufactured by sequentially laminating a sheet-shaped positive electrode plate, a separator, and a negative electrode plate on a cylindrical battery can, winding them in one direction to form a jelly roll-type electrode assembly, and then covering and sealing the upper part of the battery can with a cap plate. The positive electrode plate and the negative electrode plate are each provided with strip-shaped positive and negative electrode tabs, and the positive and negative electrode tabs are connected to electrode terminals to be electrically connected to an external power source. The positive electrode terminal is the cap plate, and the negative electrode terminal is the battery can. However, in the case of a conventional cylindrical battery having such a structure, since current concentrates on the strip-shaped electrode tabs, there are problems such as high resistance, much heat generation, and poor current collection efficiency.

[0005] On the one hand, in recent years, with the development of electric vehicle technology, the demand for high-capacity batteries has increased, and the development of large-sized cylindrical batteries with a large volume has been required. In the case of small cylindrical batteries that have been generally used in the past, that is, cylindrical batteries having a form factor of 1865 or 2170, since the capacity was small, resistance and heat generation did not seriously affect the performance of the battery. However, if the specifications of the conventional small cylindrical batteries are directly applied to large cylindrical batteries, serious problems may be caused to the safety of the batteries.

[0006] When the size of the battery increases, the amount of heat and gas generated inside the battery also increases. However, such heat and gas can cause the temperature and pressure inside the battery to rise, and the battery may catch fire or explode. To prevent this, the heat and gas inside the battery must be properly discharged to the outside. For this purpose, the cross-sectional area of the battery serving as a passage for discharging heat to the outside of the battery must increase according to the increase in volume. However, usually, the increase in the cross-sectional area does not reach the increase in volume. Therefore, as the battery becomes larger, the amount of heat generated inside the battery increases, which causes problems such as an increase in the risk of explosion and a decrease in output. In addition, when rapid charging is performed at a high voltage, a problem may also occur in that the battery catches fire due to a large amount of heat generated around the electrode tab in a short time.

[0007] Therefore, by applying a structure in which a separate electrode tab is not formed and the plain portions of the positive electrode plate and the negative electrode plate serve as the electrode tab (for example, a tab-less structure), the problem of current concentration around the electrode tab can be solved.

[0008] However, when such a tabless structure is applied, the internal space arrangement and structure are different from those of a conventional cylindrical lithium secondary battery, so it exhibits a different aspect from the characteristics of a conventional cylindrical battery. For example, in a conventional cylindrical lithium secondary battery, as the injection amount of the electrolyte increases, the electrolyte is sufficiently impregnated into the electrode assembly, so the characteristics of the lithium secondary battery tend to improve. However, in a large-capacity lithium secondary battery to which a tabless structure is applied, the internal structure and space arrangement are different from those of a conventional cylindrical lithium secondary battery, and the impregnation characteristics of the wound electrode assembly are different. Therefore, when the injection amount of the electrolyte increases, there is a problem that the impregnation property of the electrolyte decreases due to the increase in the internal pressure of the electrode assembly.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] The present invention is for solving the above problems, and aims to provide a large-capacity lithium secondary battery to which a tabless structure is applied, in which the impregnation property of the electrolyte is improved and various performances such as output and life characteristics are excellent.

MEANS FOR SOLVING THE PROBLEMS

[0010] According to one embodiment, the present invention provides a lithium secondary battery including a wound electrode assembly in which a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate are wound in one direction, a battery can in which the electrode assembly is housed, an electrolyte injected into the battery can, and a sealing member for sealing an open end of the battery can, wherein the positive electrode plate and the negative electrode plate each include a plain portion where an active material layer is not formed, and at least a part of the plain portion of the positive electrode plate or the negative electrode plate defines an electrode tab, and the occupied volume of the electrolyte is 101% by volume or more and 119% by volume or less with respect to the total pore volume of the positive electrode plate, the negative electrode plate, and the separator.

EFFECTS OF THE INVENTION

[0011] The lithium secondary battery according to the present invention may have a structure (for example, a tab-less structure) in which the electrode tabs are not formed, and the plain portions of the positive electrode plate and the negative electrode plate serve as electrode tabs. In the case of a conventional cylindrical battery with electrode tabs, a large amount of current concentrates on the electrode tabs during charging, generating a large amount of heat around the electrode tabs. In particular, during rapid charging, such a phenomenon becomes more intense, and there is a risk of battery ignition or explosion. On the other hand, the tab-less cylindrical lithium secondary battery according to the present invention forms a plain portion at the ends of the positive electrode plate and the negative electrode plate where the active material layer is not formed, and may be connected to the electrode terminal by welding the plain portion to a current collector plate having a large cross-sectional area. Such a tab-less battery has less current concentration compared to a conventional battery with electrode tabs, so it can effectively reduce heat generation inside the battery, thereby obtaining the effect of improving the thermal stability of the battery.

[0012] In addition, the lithium secondary battery according to the present invention is also applicable to a large-capacity cylindrical lithium secondary battery with a tab-less structure in which the occupied volume of the electrolyte is adjusted to be 101% by volume or more and 119% by volume or less with respect to the total pore volume of the positive electrode plate, the negative electrode plate, and the separator, so that the electrolyte is sufficiently impregnated into the electrode assembly, and the effects of excellent output characteristics and life characteristics can be obtained. In particular, it is possible to reduce the loss of available electrolyte and realize a large-capacity lithium secondary battery with excellent low-temperature life characteristics.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described more specifically.

[0015] The terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. Instead, in accordance with the principle that the inventor can appropriately define the concept of a term in order to best explain his or her invention, they should be construed in a meaning and concept consistent with the technical idea of the present invention.

[0016] In the present invention, the "primary particle" means a particle unit in which no grain boundaries are present in appearance when observed at a magnification of 5000 to 20000 times using a scanning electron microscope. The "average particle size of primary particles" means the arithmetic mean value calculated after measuring the particle sizes of the primary particles observed from a scanning electron microscope image.

[0017] In the present invention, the "secondary particle" is a particle formed by the aggregation of a plurality of primary particles. In the present invention, in order to distinguish it from the conventional secondary particles formed by the aggregation of several tens to several hundreds of primary particles, the secondary particle formed by the aggregation of 10 or fewer primary particles is referred to as a pseudo single particle.

[0018] In the present invention, "D 50 " means the particle size at the 50% reference of the volume cumulative particle size distribution of the positive electrode active material powder, and can be measured using the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000), irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, then a volume cumulative particle size distribution graph is obtained, and then the particle size corresponding to 50% of the volume cumulative amount is determined to perform the measurement.

[0019] electrolyte The electrolyte contained in the lithium secondary battery of the present invention may be injected in an amount such that the occupied volume of the electrolyte is 101% by volume or more and 119% by volume or less, preferably 101% by volume or more and 115% by volume or less, and most preferably 101% by volume or more and 108% by volume or less, based on the total pore volume of the positive electrode plate, negative electrode plate, and separator. In that case, the electrode assembly can be sufficiently impregnated with the electrolyte, and the effects of excellent output characteristics and life characteristics can be obtained. In particular, when the amount of electrolyte injection is less than the above range, the amount of electrolyte solution in which lithium ions can move decreases, resulting in a decrease in output characteristics, an increase in the loss of available electrolyte, and a high precipitation ratio of lithium at low temperatures, leading to poor low-temperature life characteristics. Also, when the amount of electrolyte injection exceeds the above range, the internal pressure increases due to the increase in the amount of electrolyte, and the impregnation property of the electrolyte rather decreases, resulting in inferior output and life characteristics.

[0020] The electrolyte used in the lithium secondary battery of the present invention may have a viscosity at 20 °C of 3.5 cP or more and 4.2 cP or less, preferably 3.55 cP or more and 4.15 cP or less. The viscosity can be measured using an Ostwald viscometer. When the viscosity satisfies the above range, the impregnation property of the electrolyte reaches an appropriate level, and when the range of the electrolyte injection fraction of the present invention is applied, optimal performance can be provided.

[0021] The electrolyte used in the lithium secondary battery of the present invention may contain a lithium salt, an organic solvent, and an additive.

[0022] The lithium salt is used as an electrolyte salt in the lithium secondary battery and is used as a medium for transmitting ions. Usually, the lithium salt contains, for example, Li as a cation + and, as an anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 -, AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - At least one selected from the group consisting of is mentioned.

[0023] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10It may contain a single substance or a mixture of two or more selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide; LiFSI), LiN(SO2CF2CF3)2 (lithium bis(perfluoroethanesulfonyl)imide; LiBETI), and LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide; LiTFSI). In addition to these, lithium salts commonly used in electrolytes of lithium secondary batteries can be used without limitation.

[0024] In order to achieve optimal electrolyte impregnation for the large-capacity cylindrical lithium secondary battery, the lithium salt may be contained in the electrolyte at a concentration of 1.0 M to 1.5 M, preferably 1.1 M to 1.3 M. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics during high-temperature storage of the lithium secondary battery is sufficient, and the viscosity of the non-aqueous electrolyte is appropriate, so the impregnation of the electrolyte is improved.

[0025] The organic solvent may contain at least one or more organic solvents selected from the group consisting of cyclic carbonate-based organic solvents, linear carbonate-based organic solvents, linear ester-based organic solvents, and cyclic ester-based organic solvents.

[0026] Specifically, the organic solvent may contain a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixed organic solvent thereof.

[0027] The cyclic carbonate-based organic solvent is a high-viscosity organic solvent and has a high dielectric constant, so it is an organic solvent that easily dissociates lithium salts in the electrolyte. Specific examples thereof may include at least one or more organic solvents selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate. Among them, ethylene carbonate may be included.

[0028] The cyclic carbonate, such as ethylene carbonate, may be contained in an amount of 15 to 30% by volume, preferably 15 to 25% by volume, and most preferably 15 to 20% by volume based on the total organic solvent. When ethylene carbonate is contained within the above range, an electrolyte optimized from the viewpoints of viscosity and performance can be provided.

[0029] The linear carbonate-based organic solvent is an organic solvent having a low viscosity and a low dielectric constant. As typical examples thereof, at least one or more organic solvents selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate may be used. Specifically, ethyl methyl carbonate (EMC) may be included.

[0030] The linear carbonate, such as ethyl methyl carbonate, may be contained in an amount of 15 to 30% by volume, preferably 15 to 25% by volume, and most preferably 15 to 20% by volume based on the total organic solvent. When ethyl methyl carbonate is contained within the above range, an electrolyte optimized from the viewpoints of viscosity and performance can be provided.

[0031] The organic solvent contained in the electrolyte of the present invention includes ethylene carbonate (EC) and ethyl methyl carbonate (EMC), and preferably contains 25% by volume or less of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) based on the total volume of the organic solvent. In that case, the impregnability of the electrolyte becomes an appropriate level, and when the range of the injection fraction of the present invention is applied, the electrolyte is sufficiently impregnated into the electrode assembly. Therefore, the lithium secondary battery of the present invention can obtain the effect of being excellent in all of the output characteristics and the life characteristics.

[0032] The organic solvent may contain ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:0.25 to 1:1.15, preferably 1:0.2 to 1:1.1.

[0033] The organic solvent may further contain dimethyl carbonate (DMC) additionally.

[0034] Further, in order to produce an electrolyte having a high ionic conductivity, the organic solvent may further contain at least one or more ester-based organic solvents selected from the group consisting of linear ester-based organic solvents and cyclic ester-based organic solvents in at least one or more carbonate-based organic solvents selected from the group consisting of the cyclic carbonate-based organic solvents and the linear carbonate-based organic solvents.

[0035] Specific examples of such linear ester-based organic solvents include at least one or more organic solvents selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0036] Examples of the cyclic ester-based organic solvent include at least one or more organic solvents selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0037] On the other hand, if necessary, the organic solvent can be further used without limitation as an organic solvent commonly used in non-aqueous electrolytes. For example, it may further contain at least one or more organic solvents such as ether-based organic solvents, glyme-based solvents, and nitrile-based organic solvents.

[0038] As the ether-based solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL), or a mixture of two or more thereof may be used, but it is not limited thereto.

[0039] The glyme-based solvent has a higher dielectric constant and a lower surface tension than linear carbonate-based organic solvents, and is a solvent with less reactivity with metals, and may contain at least one selected from the group consisting of dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME), but is not limited thereto.

[0040] The nitrile-based solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0041] In addition, the non-aqueous electrolyte of the present invention may contain an electrolyte additive in order to prevent the non-aqueous electrolyte from decomposing in a high-output environment and causing the collapse of the negative electrode, or to further improve the low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, battery expansion suppression effect at high temperature, etc.

[0042] Such an electrolyte additive may include, as typical examples thereof, at least one or more additives for forming an SEI film selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0043] Examples of the cyclic carbonate compound include vinylene carbonate (VC) or vinyl ethylene carbonate.

[0044] The cyclic carbonate compound may be contained in an amount of 0.1 to 3% by weight, preferably 1 to 3% by weight, and most preferably 1.5 to 2.5% by weight based on the total weight of the electrolyte.

[0045] Examples of the halogen-substituted carbonate compound include fluoroethylene carbonate (FEC).

[0046] Examples of the sultone compound include at least one or more compounds selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0047] The sultone compound may be contained in an amount of 0.1 to 2% by weight, preferably 0.1 to 1.5% by weight, and most preferably 0.8 to 1.2% by weight based on the total weight of the electrolyte.

[0048] Examples of the sulfate compound include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0049] Examples of the phosphate compound include one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(2,2,2-trifluoroethyl)phosphite.

[0050] Examples of the borate compound include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), and lithium bisoxalate borate (LiB(C2O4)2, LiBOB).

[0051] Examples of the nitrile compound include at least one or more compounds selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0052] Examples of the benzene compound include fluorobenzene. Examples of the amine compound include triethanolamine and ethylenediamine. Examples of the silane compound include tetravinylsilane.

[0053] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples thereof include lithium difluorophosphate (LiDFP), LiPO2F2, LiBF4, etc. Among them, LiPO2F2 plays a role in reducing the increased resistance. Specifically, LiPO2F2 is reduced in the initial activation process to form an inorganic film containing F and P on the electrode, and such an inorganic film makes the durability of the SEI layer excellent and suppresses further reaction of the electrolyte. Therefore, since the increase in resistance caused by the decomposition of the electrolyte is suppressed, the resistance of the cylindrical lithium secondary battery can be reduced.

[0054] The electrolyte may contain LiPO2F2 in an amount of 0.01 to 1% by weight, preferably 0.1 to 1% by weight, more preferably 0.2 to 0.8% by weight based on the total weight of the electrolyte. When the content of LiPO2F2 satisfies the above range, an inorganic film containing an appropriate amount of F and P is formed on the electrode in the initial activation process. Therefore, the durability of the SEI layer is excellent, the effect of reducing the initial resistance is sufficient, and the effect of excellent high-temperature storage performance is achieved.

[0055] Among such other electrolyte additives, when further containing a combination of vinylene carbonate (VC), 1,3-propanesultone (PS) and lithium difluorophosphate (LiPO2F2), a more robust SEI film can be formed on the surface of the negative electrode during the initial activation process of the secondary battery, suppressing the generation of gas generated by the decomposition of the electrolyte at high temperature, and improving the high-temperature stability of the secondary battery.

[0056] The electrolyte may further contain a compound selected from the group consisting of succinonitrile, Propargyl-1H-imidazole-1-carboxylate, and Methyl-prop-2-ynyl carbonate. The electrolyte may contain succinonitrile in an amount of 0.01 to 0.5% by weight based on the total weight of the electrolyte. The electrolyte may contain Propargyl-1H-imidazole-1-carboxylate in an amount of 0.01 to 1% by weight based on the total weight of the electrolyte. The electrolyte may contain Methyl-prop-2-ynyl carbonate in an amount of 0.01 to 1% by weight based on the total weight of the electrolyte.

[0057] electrode assembly The electrode assembly is a jelly roll type electrode assembly having a structure in which a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate are wound in one direction.

[0058] The electrode assembly of the present invention can be manufactured by winding a laminate formed by sequentially laminating at least once a separator, a positive electrode plate, a separator, and a negative electrode plate in one direction.

[0059] Here, the positive electrode plate and the negative electrode plate have a structure in which an active material layer is formed on a long sheet-like current collector, and may include a blank portion where the active material layer is not formed in a part of the region of the current collector.

[0060] When the positive electrode plate and the negative electrode plate including the blank portion are used as described above, a tabless structure battery can be realized in which at least a part of the blank portions of the positive electrode plate and the negative electrode plate define electrode tabs without providing separate electrode tabs.

[0061] Specifically, the non-coated portion may be formed long along the winding direction at an end of one side of the current collector, and by connecting a current collecting plate to each of the non-coated portions of the positive electrode plate and the negative electrode plate and connecting the current collecting plate to an electrode terminal, a tab-less battery structure can be realized.

[0062] For example, a tab-less battery can be manufactured by the following method. First, a separator, a positive electrode plate, a separator, and a negative electrode plate are sequentially laminated so that the non-coated portions of the positive electrode plate and the negative electrode plate are located in opposite directions, and then wound in one direction to manufacture a jelly roll type electrode assembly. Then, the non-coated portions of the positive electrode plate and the negative electrode plate are bent in the direction of the winding center, and then a current collecting plate is welded and connected to the non-coated portions of the positive electrode plate and the negative electrode plate respectively, and the current collecting plate is connected to an electrode terminal, whereby a tab-less battery structure can be manufactured. On the other hand, the current collecting plate has a larger cross-sectional area than a strip type electrode tab, and since the resistance is inversely proportional to the cross-sectional area of the path through which the current flows, when the secondary battery has the above structure, the cell resistance can be significantly reduced.

[0063] On the other hand, the non-coated portions of the positive electrode plate and the negative electrode plate may be processed into a form of a plurality of segmented pieces that can be independently bent, and at least a part of the plurality of segmented pieces may be bent toward the winding center of the electrode assembly.

[0064] The segmented pieces may be formed by processing the current collectors of the positive electrode plate and the negative electrode plate through a metal foil cutting process such as laser notching, ultrasonic cutting, or punching.

[0065] When the non-coated portions of the positive electrode plate and the negative electrode plate are processed into a form of a plurality of segmented pieces, the stress applied to the non-coated portion during bending can be reduced to prevent deformation and damage of the non-coated portion, and the welding characteristics with the current collecting plate can be improved.

[0066] The current collector plate and the blank part are generally joined by welding. However, in order to improve the welding characteristics, a strong pressure must be applied to the welding area of the blank part to bend the blank part as flat as possible. However, in such a bending process, the shape of the blank part may be distorted and deformed irregularly, and the deformed part may contact the electrode of the opposite polarity to cause an internal short circuit, or may induce fine cracks in the blank part. However, when the blank parts of the positive electrode plate and the negative electrode plate are processed into a form of a plurality of segmented pieces that can be bent independently, the stress applied to the blank part during bending is relaxed, and the deformation and damage of the blank part can be minimized.

[0067] Also, when the blank part is processed into the form of segmented pieces as described above, the segmented pieces overlap each other during bending, thereby increasing the welding strength with the current collector plate. When using the latest technologies such as laser welding, the problem that the laser penetrates into the inside of the electrode assembly and ablates the separator and the active material can be prevented. It is preferable that at least a part of the plurality of bent segmented pieces overlap on the upper and lower ends of the electrode assembly, and the current collector plate is coupled to the overlapping plurality of segmented pieces.

[0068] Next, each component of the electrode assembly of the present invention will be described in more detail.

[0069] (1) Positive electrode plate The positive electrode plate may have a structure in which a positive electrode active material layer is formed on one or both surfaces of a long sheet-shaped positive electrode current collector. The positive electrode active material layer may contain a positive electrode active material, a conductive material, and a binder.

[0070] Specifically, the positive electrode plate can be manufactured by applying a positive electrode slurry, in which a positive electrode active material, a conductive material, and a binder are dispersed in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, onto one or both surfaces of a long sheet-shaped positive electrode current collector, removing the solvent of the positive electrode slurry by a drying process, and then rolling. On the other hand, when applying the positive electrode slurry, a positive electrode plate including a plain portion can be manufactured by a method of not applying the positive electrode slurry to a partial region of the positive electrode current collector, for example, one end portion of the positive electrode current collector.

[0071] 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 those obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may usually have a thickness of 3 to 500 μm, and the adhesion of the positive electrode active material can also be enhanced by forming fine irregularities on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0072] On the other hand, as the positive electrode active material, positive electrode active materials generally used in the art can be used.

[0073] Preferably, the positive electrode active material may contain a lithium nickel-based oxide, and specifically, may contain a lithium nickel-based oxide containing 80 mol% or more of Ni with respect to the total number of moles of transition metals. Preferably, the lithium nickel-based oxide may contain Ni in an amount of 80 mol% or more and less than 100 mol%, 82 mol% or more and less than 100 mol%, or 83 mol% or more and less than 100 mol%. As described above, when a lithium nickel-based oxide with a high Ni content is used, a high capacity can be realized.

[0074] More specifically, the positive electrode active material may contain a lithium nickel-based oxide represented by the following [Chemical Formula 1].

[0075] [Chemical Formula 1] Li a Ni b Co c M 1 d M 2 e O2

[0076] In the Chemical Formula 1, M 1 may be Mn, Al, or a combination thereof, preferably Mn or Mn and Al.

[0077] The M 2 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. The M 2 element is not necessarily included, but when included in an appropriate amount, it plays a role in promoting grain growth during firing or improving the stability of the crystal structure.

[0078] The a represents the molar ratio of lithium in the lithium nickel-based oxide, and may be 0.8 ≦ a ≦ 1.2, 0.85 ≦ a ≦ 1.15, or 0.9 ≦ a ≦ 1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide is stably formed.

[0079] The b represents the molar ratio of nickel in all metals excluding lithium in the lithium nickel-based oxide, and may be 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, it exhibits a high energy density and can achieve a high capacity.

[0080] Said c represents the molar ratio of cobalt in all metals excluding lithium in the lithium nickel-based oxide, and 0 < c < 0.2, 0 < c < 0.15, 0 < c < 0.14, or 0.01 ≦ c ≦ 0.12 may be satisfied. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0081] Said d represents the molar ratio of element M in all metals excluding lithium in the lithium nickel-based oxide, and 0 < d < 0.2, 0 < d < 0.15, 0 < d < 0.14, or 0.01 ≦ d ≦ 0.12 may be satisfied. 1 When the molar ratio of element M satisfies the above range, the structure stability of the positive electrode active material is excellent. 1

[0082] Said e represents the molar ratio of element M in all metals excluding lithium in the lithium nickel-based oxide, and 0 ≦ e ≦ 0.1 or 0 ≦ e ≦ 0.05 may be satisfied. 2

[0083] On the other hand, the positive electrode active material according to the present invention may further include a coating layer containing 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 on the surface of the particles of the lithium nickel-based oxide as necessary. Preferably, the coating element may be Al, B, Co, or a combination thereof, and most preferably, the coating element may be B.

[0084] When a coating layer exists on the surface of the particles of the lithium nickel-based oxide, the contact between the electrolyte and the lithium composite transition metal oxide is suppressed by the coating layer, and thereby the effect of reducing the elution of the transition metal and the generation of gas due to the side reaction with the electrolyte can be obtained.

[0085] ​​The positive electrode active material may be contained in an amount of 80 to 99% by weight, preferably 85 to 99% by weight, more preferably 90 to 99% by weight, based on the total weight of the positive electrode active material layer.

[0086] On the other hand, the form of the positive electrode active material is not particularly limited, and it may be in the form of secondary particles in which a plurality of primary particles are aggregated, in the form of single particles composed of one primary particle, or in a form in which they are combined.

[0087] Preferably, the positive electrode active material may include single particles composed of one primary particle and / or positive electrode active material composed of similar single particles that are aggregates of 10 or fewer primary particles. By using a positive electrode active material composed of single particles composed of one primary particle and / or similar single particles that are aggregates of 10 or fewer primary particles, it is possible to obtain a large cylindrical battery with excellent safety while achieving high capacity.

[0088] Conventionally, it has been common to use spherical secondary particles in which dozens to hundreds of primary particles are aggregated as the positive electrode active material of a lithium secondary battery. However, in the case of a positive electrode active material in the form of secondary particles in which so many primary particles are aggregated, particle breakage in which the primary particles are separated occurs easily in the rolling process during the manufacture of the positive electrode, and there is a problem that cracks occur inside the particles during the charge and discharge process. When particle breakage or cracks inside the particles of the positive electrode active material occur, the contact area with the electrolyte increases, so there is a problem that the generation of gas due to side reactions with the electrolyte increases. When the generation of gas increases inside a cylindrical battery, the pressure inside the battery increases, and there is a risk of battery explosion. In particular, when the volume of the cylindrical battery is increased, the amount of the active material inside the battery increases with the increase in volume, and thereby the amount of gas generation also increases significantly, so the risk of battery ignition and / or explosion becomes even greater.

[0089] On the other hand, the positive electrode active material in the form of single particles composed of one primary particle or similar single particles aggregated from 10 or fewer primary particles has a higher particle strength than the positive electrode active material in the form of conventional secondary particles in which dozens to hundreds of primary particles are aggregated. Therefore, almost no particle breakage occurs during rolling. Further, in the case of the positive electrode active material in the form of single particles or similar single particles, since the number of primary particles constituting the particles is small, there are few changes due to the expansion and contraction of the volume of the primary particles during charge and discharge, and thereby the generation of cracks inside the particles is also significantly reduced.

[0090] Therefore, when using a positive electrode active material composed of single particles and / or similar single particles, the amount of gas generated due to particle breakage and the generation of internal cracks can be significantly reduced, and thereby excellent safety can be realized even in a large cylindrical battery.

[0091] On the other hand, the positive electrode active material in the form of single particles and / or similar single particles is preferably contained in an amount of 95% by weight to 100% by weight, preferably 98% by weight to 100% by weight, more preferably 99% by weight to 100% by weight, and still more preferably 100% by weight based on the total weight of the positive electrode active material contained in the positive electrode active material layer. When the content of single particles and / or similar single particles satisfies the above range, sufficient safety can be obtained when applied to a large cylindrical battery.

[0092] On the other hand, the positive electrode active material in the form of single particles and / or similar single particles according to the present invention has an average particle diameter D 50 may be 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less. For example, it may be 0.5 μm to 5 μm, preferably 1 μm to 5 μm, and more preferably 2 μm to 5 μm. When the average particle diameter D 50 of the positive electrode active material satisfies the above range, an increase in resistance can be minimized.

[0093] The cathode active material in the form of single particles and / or similar single particles has a problem that the mobility of lithium is inferior to that of the cathode active material in the form of secondary particles because there are few interfaces between primary particles that serve as diffusion paths of lithium ions inside the particles, thereby increasing the resistance. Such an increase in resistance becomes more severe as the particle size increases, and an increase in resistance has an adverse effect on the capacity and output characteristics. Therefore, in the present invention, a single particle or similar single particle cathode active material having an average particle size D 50 of 5 μm or less is applied to minimize the diffusion distance of lithium ions inside the particles, thereby suppressing an increase in resistance.

[0094] The cathode active material in the form of the single particles and / or similar single particles may have an average primary particle size of 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less. For example, it may be 0.5 μm to 5 μm, preferably 1 μm to 5 μm, more preferably 2 μm to 5 μm. When the average primary particle size satisfies the above range, a cathode active material in the form of single particles and / or similar single particles having excellent electrochemical characteristics can be formed. If the average primary particle size is too small, the number of aggregated primary particles forming the cathode active material increases, and the effect of suppressing particle breakage during rolling decreases. If the average primary particle size is too large, the lithium diffusion path inside the primary particles becomes long, the resistance increases, and the output characteristics may deteriorate.

[0095] In the present invention, the cathode active material in the form of the single particles and / or similar single particles preferably has a unimodal particle size distribution. Conventionally, in order to improve the electrode density of the cathode active material layer, a bimodal cathode active material in which a large particle size cathode active material having a large average particle size and a small particle size cathode active material having a small average particle size are mixed and used has been widely used. However, in the case of a cathode active material in the form of single particles or similar single particles, when the particle size increases, the lithium migration path becomes long and the resistance increases significantly. Therefore, when large particle size particles are mixed and used, problems such as a decrease in capacity and output characteristics may occur. Therefore, in the present invention, by using a cathode active material having a unimodal distribution, an increase in resistance is minimized.

[0096] Next, the conductive material is used to impart conductivity to the electrode, and in the battery being configured, it can be used without particular limitation as long as it does not cause a chemical change and has electron conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotube; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive polymers such as polyphenylene derivatives, etc. Among them, one kind alone or a mixture of two or more kinds may be used. The conductive material may usually be contained in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight based on the total weight of the positive electrode active material layer.

[0097] The binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer rubber (EPDM rubber), sulfonated - EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. Among them, one kind alone or a mixture of two or more kinds may be used. The binder may be contained in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight based on the total weight of the positive electrode active material layer.

[0098] On one hand, an insulating layer may be further formed on the positive electrode plate according to the present invention, covering a part of the positive electrode active material layer and a part of the non-coated portion as needed. The insulating layer may be formed along a direction parallel to the winding direction of the electrode assembly.

[0099] The voids of the positive electrode plate are preferably 22 to 24% by volume, more preferably 23 to 24% by volume, based on the total volume of the positive electrode plate.

[0100] (2) Negative electrode plate The negative electrode plate may have a structure in which a negative electrode active material layer is formed on one or both sides of a long sheet-like negative electrode current collector. The negative electrode active material layer may contain a negative electrode active material, a conductive material, and a binder.

[0101] Specifically, the negative electrode plate can be manufactured by applying a negative electrode slurry, which is prepared by dispersing a negative electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, on one or both sides of a long sheet-like negative electrode current collector, removing the solvent of the negative electrode slurry by a drying process, and then rolling. On the other hand, when applying the negative electrode slurry, a negative electrode plate including a non-coated portion can be manufactured by a method of not applying the negative electrode slurry to a part of the region of the negative electrode current collector, for example, one end of the negative electrode current collector.

[0102] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; silicon-based materials such as Si, Si-Me alloy (where Me is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiOy (where 0 < y < 2), and Si-C composite; lithium metal thin film; and metal materials capable of alloying with lithium such as Sn and Al. One or a mixture of two or more of them may be used.

[0103] Preferably, the negative electrode plate according to the present invention may contain a silicon-based negative electrode active material. The silicon-based negative electrode active material may be Si, Si-Me alloy (where Me is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiOy (where 0 < y < 2), Si-C composite, or a combination thereof, and preferably, it may be SiOy (where 0 < y < 2). Since the silicon-based negative electrode active material has a high theoretical capacity, when the silicon-based negative electrode active material is included, the capacity characteristics can be improved.

[0104] On the other hand, the silicon-based negative electrode active material may be doped with a b metal, and here, the b metal may be a Group 1 metal element or a Group 2 metal element, and specifically, it may be Li, Mg, etc. Specifically, the silicon negative electrode active material may be Si, SiOy (where 0 < y < 2), Si-C composite, etc. doped with a b metal. In the case of a metal-doped silicon-based negative electrode active material, although the capacity of the active material decreases somewhat due to the doping element, since it has high efficiency, a high energy density can be realized.

[0105] Further, the silicon-based negative electrode active material may further include a carbon coating layer on the surface of the particles. Here, the amount of the carbon coating may be 20% by weight or less, preferably 1 to 20% by weight, based on the total weight of the silicon-based negative electrode active material.

[0106] Also, the negative electrode plate may further contain a carbon-based negative electrode active material as a negative electrode active material, if necessary. The carbon-based negative electrode active material may be, for example, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, etc., but is not limited thereto.

[0107] On the one hand, when a mixture of a silicon-based negative electrode active material and a carbon-based negative electrode active material is used as the negative electrode active material, the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material may be 1:99 to 20:80, preferably 1:99 to 15:85, more preferably 1:99 to 10:90 in terms of weight ratio.

[0108] The negative electrode active material may be contained in an amount of 80 to 99% by weight, preferably 85 to 99% by weight, more preferably 90 to 99% by weight based on the total weight of the negative electrode active material layer.

[0109] On the other hand, as the negative electrode current collector, a negative electrode current collector generally used in the art can be used. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those obtained by surface-treating the surface of copper or stainless steel with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. The negative electrode current collector may usually have a thickness of 3 to 500 μm. Similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the binding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0110] The conductive material is used to impart conductivity to the negative electrode. In the battery to be configured, as long as it does not cause a chemical change and has electron conductivity, it can be used without particular limitation. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube; metal powders or metal fibers such as copper, nickel, aluminum, silver; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; conductive polymers such as polyphenylene derivatives, etc. Among them, one kind alone or a mixture of two or more kinds may be used. The conductive material may usually be contained in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight based on the total weight of the negative electrode active material layer.

[0111] The binder plays a role in improving the adhesion between negative electrode active material particles and the adhesive force between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene 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 rubber (EPDM rubber), sulfonated - EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. Among them, one kind alone or a mixture of two or more kinds may be used. The binder may be contained in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight based on the total weight of the negative electrode active material layer.

[0112] The voids of the negative electrode plate are preferably 22 to 24% by volume, more preferably 23 to 24% by volume based on the total volume of the negative electrode plate.

[0113] (3) Separator The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Any material that is usually used as a separator in a lithium secondary battery can be used without particular limitation. Specifically, as the separator, a porous polymer film, for example, a porous polymer film made of a polyolefin - based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc., or a laminated structure of two or more layers thereof may be used. Also, a normal porous non - woven fabric, for example, a non - woven fabric made of high - melting - point glass fiber, polyethylene terephthalate fiber, etc. may be used. Further, a coated separator containing a ceramic component or a polymer substance may be used to ensure heat resistance or mechanical strength.

[0114] The voids of the separation membrane are preferably 46 to 47% by volume, more preferably 47 to 48% by volume, based on the total volume of the separation membrane.

[0115] cylindrical lithium secondary battery Next, the cylindrical lithium secondary battery according to the present invention will be described.

[0116] The cylindrical lithium secondary battery according to the present invention may be a large-capacity cylindrical secondary battery having a capacity of 25 Ah or more.

[0117] The cylindrical lithium secondary battery according to the present invention may be a large cylindrical battery having a form factor ratio (defined as the value obtained by dividing the diameter of the cylindrical battery by its height, i.e., the ratio of the diameter (Φ) to the height (H)) of 0.4 or more. Here, the form factor means a value indicating the diameter and height of the cylindrical battery.

[0118] The cylindrical battery according to the present invention may be, for example, a 46110 cell (diameter 46 mm, height 110 mm, form factor ratio 0.418), a 4875 cell (diameter 48 mm, height 75 mm, form factor ratio 0.640), a 48110 cell (diameter 48 mm, height 110 mm, form factor ratio 0.436), a 4880 cell (diameter 48 mm, height 80 mm, form factor ratio 0.600), a 4680 cell (diameter 46 mm, height 80 mm, form factor ratio 0.575), or a 4695 cell (diameter 46 mm, height 95 mm, form factor ratio 0.484). In the numerical value indicating the form factor, the first two digits indicate the diameter of the cell, and the next two or three digits indicate the height of the cell.

[0119] The cylindrical lithium secondary battery according to the present invention significantly reduces the amount of gas generated compared to the prior art, and thereby can achieve excellent safety even in a large cylindrical battery having a form factor ratio of 0.4 or more.

[0120] On the other hand, the cylindrical battery according to the present invention is a tab-less battery that does not include an electrode tab.

[0121] The tabless-structured battery may have a structure in which, for example, the positive electrode plate and the negative electrode plate each include a plain portion where an active material layer is not formed, the positive electrode plate plain portion and the negative electrode plate plain portion are respectively located at the upper end and the lower end of the electrode assembly, a current collector plate is coupled to the positive electrode plate plain portion and the negative electrode plate plain portion, and the current collector plate is connected to an electrode terminal.

[0122] FIG. 1 is a cross-sectional view showing a cylindrical battery with a tabless structure according to an embodiment of the present invention. Hereinafter, with reference to FIG. 1, a cylindrical battery according to an embodiment of the present invention will be described. However, FIG. 1 only shows an embodiment of the present invention, and the structure of the cylindrical battery of the present invention is not limited to the range shown in FIG. 1.

[0123] A cylindrical battery 140 according to an embodiment of the present invention includes the above-described jelly roll type electrode assembly 141, a battery can 142 in which the electrode assembly 141 is housed, and a sealing body 143 that seals an open end of the battery can 142.

[0124] Here, the positive electrode plate and the negative electrode plate of the electrode assembly may each include a plain portion where an active material layer is not formed, and may be laminated and wound so that a positive electrode plain portion and a negative electrode plain portion are respectively located at the upper end and the lower end of the electrode assembly. Since the electrode assembly has been described above, only other components excluding the electrode assembly will be described below.

[0125] The battery can 142 is a cylindrical container having an opening formed upward, and is made of a conductive metal material such as aluminum or steel. The battery can houses the electrode assembly 141 in the inner space from the upper end opening, and also houses an electrolyte (not shown).

[0126] battery can The battery can 142 functions as a negative electrode terminal that is electrically connected to the plain portion 146b of the negative electrode plate, contacts an external power source, and transmits the current applied from the external power source to the negative electrode plate.

[0127] Optionally, a beading portion 147 and a crimping portion 148 may be provided at the upper end of the battery can 142. The beading portion 147 may be formed by press-fitting the outer peripheral surface of the battery can 142 by a distance D1. The beading portion 147 can function as a support portion to which the sealing body 143 is attached, so that the electrode assembly 141 housed inside the battery can 142 does not come out from the upper end opening of the battery can 142.

[0128] The crimping portion 148 may be formed above the beading portion 147, and extends to cover a part of the outer peripheral surface and the upper surface of the cap plate 143a disposed on the beading portion 147, and has a bent shape.

[0129] Next, the sealing body 143 is for sealing the open end of the battery can 142, and includes a cap plate 143a and a first gasket 143b that provides airtightness and has insulation between the cap plate 143a and the battery can 142. Optionally, it may further include a connection plate 143c electrically and mechanically coupled to the cap plate 143a. The cap plate 143a may be crimped onto the beading portion 147 formed on the battery can 142 and fixed by the crimping portion 148.

[0130] The cap plate 143a is a component made of a conductive metal material and covers the upper end opening of the battery can 142. The cap plate 143a is electrically connected to the positive electrode plate of the electrode assembly 141 and is electrically insulated from the battery can 142 via the first gasket 143b. Therefore, the cap plate 143a can function as the positive electrode terminal of the cylindrical secondary battery. The cap plate 143a may be provided with a protruding portion 143d protruding upward from its central portion C, and the protruding portion 143d may be brought into contact with an external power source so that current is supplied from the external power source.

[0131] A first gasket 143b may be interposed between the cap plate 143a and the crimping portion 148 to ensure the airtightness of the battery can 142 and for electrical insulation between the battery can 142 and the cap plate 143a.

[0132] On the other hand, the cylindrical battery 140 according to the present invention may further include current collector plates 144 and 145 as needed. The current collector plates are coupled to the plain portions 146a of the positive electrode plate and the plain portions 146b of the negative electrode plate and are connected to electrode terminals (i.e., the positive electrode terminal and the negative electrode terminal).

[0133] Specifically, the cylindrical battery 140 according to the present invention may include a first current collector plate 144 coupled to the upper part of the electrode assembly 141 and a second current collector plate 145 coupled to the lower part of the electrode assembly 141.

[0134] It may further include the first current collector plate 144 and / or the second current collector plate 145.

[0135] The first current collector plate 144 is coupled to the upper part of the electrode assembly 141. The first current collector plate 144 is made of a conductive metal material such as aluminum, copper, nickel, etc., and is electrically connected to the plain portion 146a of the positive electrode plate. A lead 149 may be connected to the first current collector plate 144. The lead 149 may extend above the electrode assembly 141 and may be coupled to the connection plate 143c, or may be directly coupled to the lower surface of the cap plate 143a. The connection between the lead 149 and other components may be made by welding. The first current collector plate 144 is preferably formed integrally with the lead 149. In that case, the lead 149 may have a long plate shape extending outward from the central part of the first current collector plate 144.

[0136] On the other hand, the first current collector plate 144 is coupled to the end of the plain portion 146a of the positive electrode plate, and the coupling may be performed by a method such as laser welding, resistance welding, ultrasonic welding, soldering, etc.

[0137] The second current collector plate 145 is coupled to the lower part of the electrode assembly 141. The second current collector plate 145 is made of a conductive metal material such as aluminum, copper, nickel, etc., and is electrically connected to the plain part 146b of the negative electrode plate. One surface of the second current collector plate 145 may be coupled to the plain part 146b of the negative electrode plate, and the opposite surface may be coupled to the inner bottom surface of the battery can 142. Here, the coupling may be performed by methods such as laser welding, resistance welding, ultrasonic welding, soldering, etc.

[0138] On the other hand, the cylindrical battery 140 according to the present invention may further include an insulator 146 as needed. The insulator 146 may be arranged to cover the upper surface of the first current collector plate 144. By covering the first current collector plate 144 with the insulator 146, it is possible to prevent the first current collector plate 144 and the inner peripheral surface of the battery can 142 from coming into direct contact.

[0139] The insulator 146 is provided with a lead hole 151 so that a lead 149 extending upward from the first current collector plate 144 can be drawn out. The lead 149 is drawn upward through the lead hole 151 and coupled to the lower surface of the connection plate 143c or the lower surface of the cap plate 143a.

[0140] The insulator 146 may be made of an insulating polymer resin, for example, a polymer resin material such as polyethylene, polypropylene, polyimide, polybutylene terephthalate, etc.

[0141] On the other hand, the cylindrical battery 140 according to the present invention may further include a bending part 152 formed on the lower surface of the battery can 142 as needed. The bending part 152 corresponds to a region having a thinner thickness than the peripheral region on the lower surface of the battery can 142. Since the bending part 152 has a thin thickness, it is structurally weaker than the peripheral region. Therefore, when the internal pressure of the cylindrical battery 140 increases to a predetermined level or more, the bending part 152 ruptures and the gas inside the battery can 142 is discharged to the outside, preventing the battery from exploding.

[0142] Figure 2 is a cross-sectional view showing a tabless cylindrical battery according to another embodiment of the present invention. Hereinafter, with reference to Figure 2, a cylindrical battery according to another embodiment of the present invention will be described. However, Figure 2 only shows one embodiment of the present invention, and the structure of the cylindrical battery of the present invention is not limited to the range shown in Figure 2.

[0143] Referring to Figure 2, the cylindrical battery 170 according to another embodiment of the present invention has a different structure of the battery can and the sealing body compared to the cylindrical battery 140 shown in Figure 1, and the configuration of the electrode assembly and the electrolyte is substantially the same.

[0144] Specifically, the cylindrical battery 170 includes a battery can 171 through which a rivet terminal 172 is provided. The rivet terminal 172 is installed on a closed surface (the upper surface in the drawing) that is partially closed at one end of the battery can 171. The rivet terminal 172 is riveted to a through hole (the first opening at the first end) of the battery can 171 with an insulating second gasket 173 interposed therebetween. The rivet terminal 172 is exposed to the outside in the direction opposite to the direction of gravity.

[0145] The rivet terminal 172 includes a terminal exposed portion 172a and a terminal insertion portion 172b. The terminal exposed portion 172a is exposed outside the closed surface of the battery can 171. The terminal exposed portion 172a may be located at substantially the center of the partially closed surface of the battery can 171. The maximum diameter of the terminal exposed portion 172a may be even larger than the maximum diameter of the through hole formed in the battery can 171. The terminal insertion portion 172b may penetrate substantially the center of the closed surface of the battery can 171 and be electrically connected to the plain portion 146a of the positive electrode plate. The terminal insertion portion 172b may be rivet-coupled on the inner surface of the battery can 171. That is, the end portion of the terminal insertion portion 172b may have a shape bent toward the inner surface of the battery can 171. The maximum diameter of the end portion of the terminal insertion portion 172b may be even larger than the maximum diameter of the through hole of the battery can 171.

[0146] The lower end surface of the terminal insertion portion 172b may be welded to the first current collector plate 144 connected to the non-coated portion 146a of the positive electrode plate. An insulating cap 174 made of an insulating material may be interposed between the first current collector plate 144 and the inner surface of the battery can 171. The insulating cap 174 covers the upper portion of the first current collector plate 144 and the upper edge portion of the electrode assembly 141. Thereby, it is possible to prevent the non-coated portion B3 on the outer peripheral side of the electrode assembly 141 from contacting the inner surface of the battery can 171 having a different polarity and causing a short circuit. The terminal insertion portion 172b of the rivet terminal 172 may penetrate the insulating cap 174 and be welded to the first current collector plate 144.

[0147] The second gasket 173 is interposed between the battery can 171 and the rivet terminal 172 to prevent the battery can 171 and the rivet terminal 172 having opposite polarities from coming into electrical contact with each other. Thereby, the upper surface of the battery can 171 having a substantially flat shape can function as the positive electrode terminal of the cylindrical battery 170.

[0148] The second gasket 173 includes a gasket exposed portion 173a and a gasket insertion portion 173b. The gasket exposed portion 173a is interposed between the terminal exposed portion 172a of the rivet terminal 172 and the battery can 171. The gasket insertion portion 173b is interposed between the terminal insertion portion 172b of the rivet terminal 172 and the battery can 171. The gasket insertion portion 173b may be deformed together with the terminal insertion portion 172b during riveting and be in close contact with the inner surface of the battery can 171. The second gasket 173 may be made of, for example, an insulating polymer resin.

[0149] The gasket exposed portion 173a of the second gasket 173 may have a shape that extends to cover the outer peripheral surface of the terminal exposed portion 172a of the rivet terminal 172. When the second gasket 173 covers the outer peripheral surface of the rivet terminal 172, it is possible to prevent a short circuit from occurring during the process of coupling an electrical connection component such as a bus bar to the upper surface of the battery can 171 and / or the rivet terminal 172. Although not shown in the drawings, the gasket exposed portion 173a may have a shape that extends to cover not only the outer peripheral surface of the terminal exposed portion 172a but also a part of the upper surface.

[0150] When the second gasket 173 is made of a polymer resin, the second gasket 173 may be coupled to the battery can 171 and the rivet terminal 172 by heat fusion. In that case, the airtightness at the coupling interface between the second gasket 173 and the rivet terminal 172 and at the coupling interface between the second gasket 173 and the battery can 171 is enhanced. On the other hand, when the gasket exposed portion 173a of the second gasket 173 has a shape that extends to the upper surface of the terminal exposed portion 172a, the rivet terminal 172 may be integrally coupled to the second gasket 173 by insert injection.

[0151] Among the upper surface of the battery can 171, another region 175 excluding the region occupied by the rivet terminal 172 and the second gasket 173 corresponds to a negative electrode terminal having a polarity opposite to that of the rivet terminal 172.

[0152] The second current collector plate 176 is coupled to the lower part of the electrode assembly 141. The second current collector plate 176 is made of a conductive metal material such as aluminum, steel, copper, nickel, etc., and is electrically connected to the plain portion 146b of the negative electrode plate.

[0153] The second current collector plate 176 is preferably electrically connected to the battery can 171. For this purpose, at least a part of the edge of the second current collector plate 176 may be fixed by being interposed between the inner surface of the battery can 171 and the first gasket 178b. In one example, at least a part of the edge of the second current collector plate 176 may be fixed to the beading portion 180 by welding while being supported by the lower end surface of the beading portion 180 formed at the lower end of the battery can 171. In a modified example, at least a part of the edge of the second current collector plate 176 may be directly welded to the inner wall surface of the battery can 171.

[0154] The second current collector plate 176 may be provided with a plurality of irregularities (not shown) formed radially on the surface facing the plain portion 146b. When the irregularities are formed, the second current collector plate 176 may be pushed to press-fit the irregularities into the plain portion 146b.

[0155] The second current collector plate 176 and the end of the plain portion 146b are preferably joined by welding, for example, laser welding.

[0156] The sealing body 178 that seals the lower open end of the battery can 171 includes a cap plate 178a and a first gasket 178b. The first gasket 178b electrically isolates the cap plate 178a and the battery can 171. The crimping portion 181 fixes both the edge of the cap plate 178a and the first gasket 178b together. The cap plate 178a is provided with a vent portion 179. The configuration of the vent portion 179 is substantially the same as that of the above-described embodiment.

[0157] The cap plate 178a is preferably made of a conductive metal material. However, since the first gasket 178b is interposed between the cap plate 178a and the battery can 171, the cap plate 178a does not have an electrical polarity. The sealing body 178 seals the lower open end of the battery can 171 and functions to discharge gas when the internal pressure of the battery cell 170 increases above a threshold value.

[0158] The rivet terminal 172 electrically connected to the plain portion 146a of the positive electrode plate is preferably used as the positive electrode terminal. Also, a portion 175 of the upper surface of the battery can 171, excluding the rivet terminal 172, which is electrically connected to the plain portion 146b of the negative electrode plate via the second current collector plate 176, is used as the negative electrode terminal. When the two electrode terminals are located at the upper part of the cylindrical battery in this way, it is possible to arrange electrical connection components such as a bus bar only on one side of the cylindrical battery 170. This can lead to the simplification of the battery pack structure and the improvement of the energy density. Further, since the portion 175 used as the negative electrode terminal has a substantially flat shape, a sufficient bonding area can be ensured in the bonding of electrical connection components such as a bus bar. Thereby, the cylindrical battery 170 can reduce the resistance at the bonding site of the electrical connection components to a preferable level.

[0159] When the cylindrical lithium secondary battery has the tabless structure as described above, since there is less current concentration compared to the conventional battery provided with electrode tabs, heat generation inside the battery can be effectively reduced, and thereby the effect of improving the thermal stability of the battery can be obtained.

[0160] Hereinafter, the present invention will be described in more detail with specific examples.

[0161] Example] Example 1 An organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 20:5:75 by volume ratio) was dissolved so that LiPF6 became 1.3 M to produce a non-aqueous solvent. With respect to the total weight of the electrolyte, vinylene carbonate (VC) was 2 wt%, 1,3 - propane sultone (PS) was 1 wt%, succinonitrile was 0.2 wt%, propargyl - 1H - imidazole - 1 - carboxylate was 0.3 wt%, and LiPO2F2 was 0.2 wt% were added to produce an electrolyte. The viscosity of the produced electrolyte at 20 °C was 4.1 cP. ​

[0162] Average particle size D 50 has a unimodal particle size distribution with an average particle size D of 3 μm and is in the form of single particles, and the cathode active material Li[Ni 0.9 Co 0.06 Mn 0.03 Al 0.01 O2: carbon nanotubes: PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 97.8:0.6:1.6 to produce a cathode slurry. The cathode slurry was applied to one side of an aluminum current collector sheet, dried at 120 °C, and then rolled to produce a cathode plate.

[0163] Anode active material (mixture of graphite:SiO with a weight ratio of 95:5): conductive material (super C): styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 96:2:1.5:0.5 to produce an anode slurry. The anode slurry was applied to one side of a copper current collector sheet, dried at 150 °C, and then rolled to produce an anode plate.

[0164] A separator was interposed between the cathode plate and the anode plate manufactured as described above, and they were laminated in the order of separator / cathode plate / separator / anode plate, and then wound up to produce a jelly roll type electrode assembly. The electrode assembly manufactured as described above was inserted into a cylindrical battery can. Then, a 4680 cell was manufactured by injecting the electrolyte so that the occupied volume of the electrolyte was 101% by volume with respect to the total pore volume of the cathode plate, the anode plate, and the separator.

[0165] Example 2 A 4680 cell was manufactured in the same manner as in Example 1, except that the electrolyte was injected so that the occupied volume of the electrolyte was 116% by volume with respect to the total pore volume of the cathode plate, the anode plate, and the separator.

[0166] Example 3 An organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 20:5:75 by volume ratio) was dissolved so that LiPF6 was 1.2 M to produce a non-aqueous solvent. Based on the total weight of the electrolyte, vinylene carbonate (VC) was 2 wt%, 1,3-propane sultone (PS) was 1 wt%, succinonitrile was 0.2 wt%, propargyl-1H-imidazole-1-carboxylate was 0.3 wt%, and LiPO2F2 was 0.2 wt% were added to produce an electrolyte. The viscosity of the produced electrolyte at 20 °C was 3.5 cP.

[0167] A 4680 cell was produced in the same manner as in Example 1 except that the electrolyte was injected.

[0168] Comparative Example 1 A 4680 cell was produced in the same manner as in Example 1 except that the electrolyte was injected so that the occupied volume of the electrolyte was 100% by volume with respect to the total pore volume of the positive electrode plate, negative electrode plate, and separator.

[0169] Comparative Example 2 A 4680 cell was produced in the same manner as in Example 1 except that the electrolyte was injected so that the occupied volume of the electrolyte was 120% by volume with respect to the total pore volume of the positive electrode plate, negative electrode plate, and separator.

[0170] Experimental Example - Low Temperature Life Characteristic Evaluation The low temperature life characteristics of the 4680 cells of Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated.

[0171] Specifically, for each of the 4680 cells of Examples 1 to 3 and Comparative Examples 1 and 2, charging to 4.2 V at a constant current of 0.5C at 20 °C and discharging to 2.5 V at a constant current of 0.5C were defined as one cycle, and 150 cycles of charge and discharge were performed. Then, the capacity retention rate with respect to the initial capacity after 150 cycles was measured. The results are shown in Table 1 below.

[0172]

Table 1

[0173] As shown in Table 1 above, the lithium secondary batteries in Examples 1 to 3, in which the liquid injection fraction was adjusted so that the occupied volume of the electrolyte was 101% by volume or more and 119% by volume or less with respect to the total pore volume of the positive electrode plate, the negative electrode plate, and the separator, were confirmed to have excellent low-temperature life characteristics compared to the lithium secondary batteries of Comparative Examples 1 and 2 in which the liquid was injected outside the above range.

Claims

1. A lithium secondary battery comprising a positive electrode plate, a negative electrode plate, and an electrode assembly in which a separator interposed between the positive electrode plate and the negative electrode plate is wound in one direction, a battery can housing the electrode assembly, an electrolyte injected into the battery can, and a sealing body for sealing an open end of the battery can, wherein the positive electrode plate and the negative electrode plate each include a plain portion where an active material layer is not formed, and at least a part of the plain portion of the positive electrode plate or the negative electrode plate defines an electrode tab, the lithium secondary battery, wherein an occupied volume of the electrolyte is 101% by volume or more and 119% by volume or less with respect to a total pore volume of the positive electrode plate, the negative electrode plate, and the separator.

2. The lithium secondary battery according to claim 1, wherein an occupied volume of the electrolyte is 101% by volume or more and 115% by volume or less with respect to a total pore volume of the positive electrode plate, the negative electrode plate, and the separator.

3. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has a capacity of 25 Ah or more.

4. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is a cylindrical battery having a form factor ratio of 0.4 or more.

5. The positive electrode plate includes a positive electrode active material layer containing a positive electrode active material, The lithium secondary battery according to claim 1, wherein the positive electrode active material is a lithium nickel-based oxide represented by the following [Chemical Formula 1]. [Chemical Formula 1] Li ａ Ni ｂ Co ｃ M １ ｄ M ２ ｅ O ２ In the above Chemical 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, 0 ≤ e ≤ 0.

1.

6. The negative electrode plate includes a negative electrode active material layer containing a negative electrode active material, The lithium secondary battery according to claim 1, wherein the negative electrode active material contained in the negative electrode active material layer is a mixture of a silicon-based negative electrode active material and a carbon-based negative electrode active material.

7. The lithium secondary battery according to claim 6, wherein the silicon-based negative electrode active material is SiO y (0 < y < 2), and SiO y (0 < y < 2) is contained in an amount of 1% by weight or more and 5% by weight or less based on a total weight of the negative electrode active material.

8. The lithium secondary battery according to claim 1, wherein a viscosity of the electrolyte at 20°C is 3.5 cP or more and 4.2 cP or less.

9. The lithium secondary battery according to claim 1, wherein the electrolyte contains a lithium salt, and a concentration of the lithium salt is 1.0 M or more and 1.5 M or less.

10. The lithium secondary battery according to claim 1, wherein the electrolyte contains an organic solvent, and the organic solvent includes ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

11. The lithium secondary battery according to claim 10, wherein the organic solvent contains ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:0.25 to 1:1.

15.

12. The lithium secondary battery according to claim 10, wherein the organic solvent further contains dimethyl carbonate (DMC) additionally.

13. The lithium secondary battery according to claim 10, wherein the organic solvent contains ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in an amount of 25% by volume or less based on the total volume of the organic solvent.

14. The lithium secondary battery according to claim 1, wherein the electrolyte contains vinylene carbonate in an amount of 0.1% by weight or more and 3% by weight or less based on the total weight of the electrolyte.

15. The lithium secondary battery according to claim 1, wherein the electrolyte contains 1,3 - propane sultone in an amount of 0.1% by weight or more and 2% by weight or less based on the total weight of the electrolyte.

16. The electrolyte contains lithium difluorophosphate (LiPO ２ F ２ ) in an amount of 0.01% by weight or more and 1% by weight or less based on the total weight of the electrolyte, and the lithium secondary battery according to any one of claims 1 to 15.

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