Lithium secondary battery

Abstract

This invention relates to a lithium secondary battery, comprising a battery casing and an electrode assembly and an electrolyte housed within the battery casing, wherein the value of G, as defined by the following mathematical formula (1), is between 1.8 and 3.5. Mathematical formula (1): where, in the above mathematical formula (1), V CH V represents the volume (in mL) of hydrocarbon gases present in a lithium-ion secondary battery. CO V is the volume (in mL) of carbon oxide gases present in a lithium secondary battery. total The total volume of gas present in the lithium secondary battery (unit: mL) is C, which is the discharge capacity of the lithium secondary battery when charged and discharged at a voltage range of 0.33 C and 2.5 V to 4.2 V.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2023-0190459, filed on December 22, 2023, the disclosure of which is incorporated herein by reference.

[0002] This invention relates to a lithium secondary battery, and more specifically to a lithium secondary battery designed such that the gas composition in the formed secondary battery meets specific conditions. Background Technology

[0003] With the technological development of electric vehicles, mobile electronic devices, and other technologies, the demand for lithium-ion batteries as an energy source is rapidly increasing.

[0004] Lithium-ion secondary batteries are classified into cylindrical, prismatic, and pouch batteries based on the shape of their casings. Cylindrical batteries are formed as follows: sheet-shaped positive electrodes, separators, and negative electrodes are sequentially stacked, and then the stacked assembly is wound in one direction to create a jelly-roll-type electrode assembly. This electrode assembly is housed within a cylindrical battery casing, and a cover plate is used to seal the top of the casing. The positive and negative electrodes each include strip-shaped positive and negative tabs, which are connected to electrode terminals for electrical connection to an external power source. The positive terminal serves as the cover plate, and the negative terminal serves as the battery casing.

[0005] Previously, small cylindrical secondary batteries with shape factors of 1865 (18 mm diameter × 65 mm height) or 2170 (21 mm diameter × 70 mm height) were mainly used. However, recently, with the increasing demands for driving range and fast charging speed of electric vehicles, the development and use of large cylindrical secondary batteries with larger shape factors, such as 4680 (46 mm diameter × 80 mm height), are being considered.

[0006] Meanwhile, due to the large capacity of large cylindrical secondary batteries, the increased current concentrated at the electrode tabs when using strip-shaped electrode tabs as in traditional small cylindrical secondary batteries leads to increased resistance and heat generation, resulting in reduced current collection efficiency. Therefore, a so-called tabless-less cylindrical secondary battery has been proposed, which does not use separate strip-shaped electrode tabs but instead uses the current collector itself, with the uncoated portions of both the positive and negative electrodes, as the electrode tabs.

[0007] Cylindrical secondary batteries with tabless structures not only offer relatively large capacity characteristics and energy density, but also have the advantages of improving the production efficiency and reducing the production cost of cylindrical secondary batteries for electric vehicles. Furthermore, due to the tabless structure, the number of components is reduced while increasing the electrical connection (contact) area between the electrode tabs and terminals, and the electron travel distance is reduced, thereby improving output characteristics and dispersing the heat generated during charging and discharging.

[0008] However, large cylindrical secondary batteries employing tabless structures require a pressurization process on the uncoated sections to ensure sufficient weldability to the casing and terminals. This process blocks the electrolyte movement path between the positive, separator, and negative electrodes within the wound electrode assembly, hindering normal electrolyte movement and reducing electrolyte impregnation. Consequently, the composition of the SEI film formed during formation changes, and the decomposition of the electrolyte solvent increases during battery operation. Therefore, when large cylindrical secondary batteries use the same electrolyte system as traditional small cylindrical secondary batteries, it is difficult to achieve the desired electrochemical performance.

[0009] Therefore, technological development is needed to achieve excellent electrochemical performance in large cylindrical secondary batteries suitable for medium and large-sized equipment such as vehicles. Summary of the Invention

[0010] Technical issues

[0011] The present invention aims to solve the above problems by providing a lithium secondary battery designed to satisfy specific conditions for the gas composition present in the secondary battery after formation, thereby exhibiting excellent electrochemical performance.

[0012] Technical solution

[0013] According to one embodiment, the present invention provides a lithium secondary battery comprising a battery casing and an electrode assembly and an electrolyte housed in the battery casing, wherein the electrode assembly comprises a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, and the electrolyte comprises a lithium salt and an organic solvent, and has a G value of 1.8 to 3.5, preferably 2.0 to 3.0, as defined by the following mathematical formula (1).

[0014] Mathematical formula (1):

[0015] In the mathematical formula (1) above, V CH V represents the volume of hydrocarbon gases present in the lithium-ion secondary battery after formation, expressed in mL. COV represents the volume of carbon oxide gases present in the lithium-ion secondary battery after formation, expressed in mL. total The total volume of gas present in the lithium secondary battery after formation is expressed in mL, and C is the discharge capacity of the lithium secondary battery when charged and discharged at a voltage range of 0.33 C and 2.5 V to 4.2 V.

[0016] Meanwhile, the difference between the volume of hydrocarbon gases and the volume of carbon oxide gases, relative to the total volume of gases present in the lithium secondary battery after formation, i.e. (V CH - V CO ) / V total It can be from 0.40 to 0.85, preferably from 0.45 to 0.8.

[0017] When charged and discharged at a voltage range of 0.33C and 2.5V to 4.2V, the discharge capacity C of the lithium secondary battery can be from 20Ah to 50Ah, preferably from 20Ah to 45Ah, and more preferably from 22Ah to 40Ah.

[0018] Meanwhile, the lithium salt contained in the electrolyte may include LiPF6, the organic solvent may include ethylene carbonate, and the E value of the electrolyte, as defined by the following mathematical formula (2), may be 15 to 20, preferably greater than 15 and less than 18, more preferably 15.1 to 17.9.

[0019] Mathematical expression (2):

[0020] In mathematical formula (2), M EC M represents the number of moles of ethylene carbonate in the electrolyte. LiPF6 M represents the number of moles of LiPF6 in the electrolyte. Solvent The total number of moles of the organic solvent in the electrolyte, MW EC A is the molecular weight of ethylene carbonate, A is the solubility constant of LiPF6 in the electrolyte, and C is the discharge capacity of the lithium secondary battery when charged and discharged in a voltage range of 0.33 C and 2.5 V to 4.2 V.

[0021] At this point, the number of moles of ethylene carbonate M in the electrolyte is... EC The amount can be from 0.070 to 0.090 mol, preferably from 0.075 to 0.085 mol, more preferably from 0.078 to 0.085 mol, where M is the number of moles of LiPF6 in the electrolyte. LiPF6 The amount can be 0.3 to 0.5 mol, preferably 0.3 to 0.4 mol, and more preferably 0.32 to 0.35 mol.

[0022] In addition, the total number of moles M of the organic solvent in the electrolyte SolventThe amount can be 0.30 to 0.40 mol, preferably 0.30 to 0.38 mol, more preferably 0.32 to 0.35 mol, and the solubility constant A of LiPF6 in the electrolyte can be 3 to 4, preferably 3.5.

[0023] Meanwhile, the lithium secondary battery can be a cylindrical battery with a diameter (r) to height (h) ratio of the battery casing, i.e., a shape factor ratio of 0.4 or higher, preferably 0.4 to 0.6. For example, the lithium secondary battery can be a 46110 cell, a 48110 cell, a 4880 cell, or a 4680 cell.

[0024] The lithium secondary battery may include uncoated portions on at least a portion of the positive electrode and the negative electrode where no active material layer is formed, and the uncoated portions of the positive electrode or the negative electrode may each be defined as electrode tabs.

[0025] At this time, the uncoated portion of the positive electrode and the uncoated portion of the negative electrode can be formed at the ends of the positive electrode and the negative electrode respectively along the winding direction of the electrode assembly. The current collector can be engaged with the uncoated portion of the positive electrode and the uncoated portion of the negative electrode respectively, and the current collector can be connected to the electrode terminal.

[0026] In addition, the uncoated portions of the positive and negative electrodes can be processed into multiple segmented pieces that can be bent independently. At least a portion of the multiple segmented pieces can be bent toward the winding center of the electrode assembly. At least a portion of the bent multiple segmented pieces can overlap each other on the upper and lower sides of the electrode assembly, and the current collector can be attached to the overlapping multiple segmented pieces.

[0027] According to another embodiment, the present invention provides a battery pack comprising the aforementioned lithium secondary battery of the present invention as a unit cell.

[0028] Beneficial effects

[0029] Because the lithium-ion secondary battery of the present invention is designed such that the gas composition in the cell meets specific conditions, the shortened lifespan caused by the decomposition and regeneration of the SEI and CEI films during charging and discharging, as well as the decomposition of organic solvents in the electrolyte, can be minimized. Since the gases present in the lithium-ion secondary battery are generated by interfacial reactions between the electrodes and the electrolyte, the process of film formation and change on the electrode surface can be inferred from the gas composition ratio. A gas composition in the lithium-ion secondary battery that meets the scope of the present invention means that films are stably formed on the surfaces of the positive and negative electrodes. Once a film is stably formed on the electrode surface, additional interfacial reactions between the electrodes and the electrolyte can be suppressed during cycling or storage, thereby achieving stable cell performance.

[0030] Furthermore, when the gas composition conditions of the present invention are met, large cylindrical batteries or batteries with tabless structures that have relatively low electrolyte impregnation can also have excellent life characteristics. Attached Figure Description

[0031] Figure 1 This is a diagram showing the stacked state of the electrode assembly of the present invention before winding.

[0032] Figure 2 This is a cross-sectional view showing the structure of the electrode plate of an electrode assembly according to one embodiment of the present invention.

[0033] Figure 3 This is a diagram illustrating the structure of an electrode assembly according to one embodiment of the present invention.

[0034] Figure 4 This is a cross-sectional view showing the structure of a lithium secondary battery according to one embodiment of the present invention.

[0035] Figure 5 This is a cross-sectional view showing the structure of a lithium secondary battery according to another embodiment of the present invention.

[0036] Figure 6 This is a diagram illustrating the battery pack of the present invention. Detailed Implementation

[0037] It will be understood that the terms or words used in the specification and claims should not be interpreted as having the meaning defined in a common dictionary, and it will also be understood that, based on the principle that the inventors may appropriately define the meaning of a term or word to best interpret the invention, the term or word should be interpreted as having a meaning consistent with its meaning in the context of the related technology and the technical idea of ​​the invention.

[0038] The invention will be described in more detail below.

[0039] As a result of repeated research by the inventors in order to achieve excellent electrochemical performance in large batteries or batteries with tabless structures with relatively low electrolyte impregnation, the inventors discovered that when the gas composition in the secondary battery after formation meets specific conditions, the reduction in lifetime characteristics caused by the decomposition and regeneration of the SEI film and the decomposition of organic solvents in the electrolyte during charging and discharging can be minimized. Thus, the inventors completed this invention.

[0040] Specifically, the lithium secondary battery of the present invention may include a battery casing, an electrode assembly housed in the battery casing, and an electrolyte, and the G value defined by the following mathematical formula (1) may be 1.8 to 3.5, preferably 2.0 to 3.0.

[0041] Mathematical formula (1):

[0042] In the mathematical formula (1) above, V CH The volume of hydrocarbon gas present in the lithium secondary battery after formation is expressed in mL. The hydrocarbon gas can be, for example, CH4, C2H6, etc.

[0043] V CO The volume of carbon oxide gas present in the lithium secondary battery after formation is expressed in mL. The carbon oxide gas can be, for example, CO or CO2.

[0044] V total This represents the total volume of gases present in the lithium secondary battery after formation, expressed in mL.

[0045] Meanwhile, C is the discharge capacity of the lithium secondary battery when charged and discharged in a voltage range of 0.33 C and 2.5 V to 4.2 V, which can be from 20 Ah to 50 Ah, preferably from 20 Ah to 45 Ah, and more preferably from 22 Ah to 40 Ah.

[0046] In the formation process of lithium-ion secondary batteries, the solvents and additives in the electrolyte undergo redox reactions at the surfaces of the positive and negative electrodes, forming a solid electrolyte interphase (SEI) film and a cathode electrolyte interphase (CEI) film, which serve as passive state films. During the redox reactions of the electrolyte components, gases are generated. Hydrocarbon gases are mainly generated during the formation of the SEI film at the negative electrode, while carbon oxide gases are mainly generated during the formation of the CEI film at the positive electrode. Therefore, the degree of passive state film formation on the positive and negative electrode surfaces can be estimated by analyzing the gas composition of the battery after formation.

[0047] Meanwhile, if too few SEI and CEI films are formed, side reactions on the electrolyte and electrode surfaces increase, leading to electrode degradation, increased gas generation, and ultimately, a decline in lifetime performance. Conversely, if too many SEI and CEI films are formed, the electrode surface resistance increases. Furthermore, if either the SEI or CEI film is too abundant or insufficient, an imbalance between the positive and negative electrodes may accelerate electrode degradation and reduce lifetime performance. Therefore, to achieve excellent electrochemical performance in secondary batteries, it is necessary to form appropriate amounts of SEI and CEI films.

[0048] The degree of SEI and CEI film formation varies under complex influences, including electrolyte composition, secondary battery capacity, and electrode assembly or battery shape. This is because the degree of redox reaction on the positive and negative electrode surfaces varies with electrolyte composition, while electrolyte wettability and reaction surface area vary with battery capacity or shape. Because the degree of SEI and CEI film formation varies under these complex factors, it has traditionally been difficult to determine the correlation between the degree of SEI and CEI film formation and secondary battery performance.

[0049] However, as a result of repeated research conducted by the inventors, it was found that the degree of formation of SEI and CEI films can be represented by G, which is a specific relationship between the gas composition and battery capacity in the secondary battery after formation. When the value of G is in the range of 1.8 to 3.5, the electrochemical performance of the secondary battery (especially the large-capacity battery with low electrolyte impregnation) is significantly improved.

[0050] Specifically, a G value less than 1.8 indicates excessive positive electrode side reactions during formation, leading to an increase in the amount of carbon oxide gases. Under these circumstances, the positive electrode resistance may increase, resulting in increased cell resistance and decreased energy density. Conversely, a G value greater than 3.5 indicates excessive negative electrode side reactions during formation, leading to an increase in the amount of hydrocarbon gases. This accelerates the degradation of the negative electrode, potentially reducing its lifespan.

[0051] Preferably, in the above mathematical formula (1), (V CH - V CO ) / V total The value can be from 0.40 to 0.85, especially from 0.45 to 0.8. When the gas composition in the electrolyte is within the above range, passive films of the positive and negative electrodes can be appropriately formed, resulting in excellent resistance and lifetime characteristics.

[0052] Meanwhile, by appropriately adjusting the composition of the electrolyte according to the shape of the battery casing, the shape of the electrode assembly and the battery capacity, a lithium secondary battery with a G value in the range of 1.8 to 3.5 of the above mathematical formula (1) can be prepared.

[0053] For example, the lithium secondary battery of the present invention that satisfies the G value can be prepared by adjusting the electrolyte composition per unit capacity so that the E value defined by the following mathematical formula (2) satisfies 15 to 20, preferably greater than 15 and less than 18, more preferably 15.1 to 17.9.

[0054] Mathematical expression (2):

[0055] In the mathematical expression (2) above, the aforementioned M EC This refers to the number of moles of ethylene carbonate in the electrolyte, but it is not limited to this; however, the above M...EC The amount can be from 0.070 to 0.090 mol, preferably from 0.075 to 0.085 mol, and more preferably from 0.078 to 0.085 mol. When the molar amount of ethylene carbonate in the electrolyte is within the above range, a stable membrane reaction can be induced during the formation process.

[0056] The above M LiPF6 This refers to the number of moles of LiPF6 in the electrolyte, but it is not limited to this. However, the above M... LiPF6 The molar amount of LiPF6 in the electrolyte can be 0.3 to 0.5 mol, preferably 0.3 to 0.4 mol, and more preferably 0.32 to 0.35 mol. When the molar amount of LiPF6 in the electrolyte is within the above range, a passive film can be stably formed during the formation process, resulting in a battery with excellent long-term durability and impregnation properties. If the molar amount of LiPF6 is too large, the generation of Lewis acid components such as HF may lead to increased gas production and electrode degradation, and the viscosity of the electrolyte may increase, reducing impregnation properties. Simultaneously, if the molar amount of LiPF6 is too small, the proportion of unbound free EC in the electrolyte may increase, leading to increased side reactions. Ethyl carbonate with a high dielectric constant binds to lithium ions while dissociating LiPF6; thus, ethylene carbonate bound to lithium ions is called solvated EC, while ethylene carbonate not bound to lithium ions is called free EC. Since free EC has low electrochemical stability, side reactions increase when the proportion of free EC in the electrolyte increases. However, if the proportion of free EC is too low, it may negatively affect film formation. Therefore, in order to stably form a passive film to improve electrolyte impregnation and long-term battery durability, the preferred molar number of LiPF6 is included within the scope of this invention.

[0057] M Solvent This refers to the total number of moles of organic solvent in the electrolyte, but it is not limited to this. However, the above M... Solvent The total amount of organic solvent in the electrolyte can be 0.30 to 0.40 mol, preferably 0.30 to 0.38 mol, and more preferably 0.32 to 0.35 mol. When the total number of moles of organic solvent in the electrolyte is within the above range, the electrolyte exhibits excellent viscosity and conductivity.

[0058] The above MW EC This is the molecular weight of ethylene carbonate, which is 88.06 g / mol.

[0059] The above-mentioned A is the solubility constant of LiPF6 in the electrolyte, which can vary with the composition of the organic solvent in the electrolyte and the type and content of additives. In this invention, the above-mentioned A can be 3 to 4, preferably 3.5.

[0060] When the E value defined by the above mathematical formula (2) is in the range of 15.0 to 20, the SEI film and CEI film can be appropriately formed during the formation process, and the G value can be formed in the range of 1.8 to 3.5 for the gas composition in the secondary battery.

[0061] The components of the lithium secondary battery of the present invention will now be described in more detail.

[0062] The lithium secondary battery of the present invention includes: an electrolyte; an electrode assembly including a positive electrode, a negative electrode and a separator; and a battery casing housing the electrode assembly and the electrolyte.

[0063] electrolytes

[0064] The electrolyte of the present invention comprises a lithium salt containing LiPF6 and an organic solvent containing ethylene carbonate.

[0065] The electrolyte of the present invention is preferably prepared by adjusting the molar amounts of LiPF6, ethylene carbonate and organic solvent, as well as the types and amounts of additives, so that the E value of the aforementioned mathematical formula (2) is in the range of 15.0 to 20.

[0066] Additionally, when necessary, the electrolyte of the present invention may also include at least one of the following: cyclic carbonate organic solvents other than ethylene carbonate (EC), linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

[0067] Cyclic carbonate organic solvents are organic solvents with high viscosity. As a representative example, they may include at least one organic solvent selected from the group consisting of propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentene carbonate, 2,3-pentene carbonate, and vinylene carbonate.

[0068] In addition, linear carbonate organic solvents are organic solvents with low viscosity and low dielectric constant. As a representative example, they may include at least one organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methyl ethyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate, and in particular may include methyl ethyl carbonate (EMC).

[0069] Straight-chain ester organic solvents may include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate as specific examples.

[0070] Cyclic ester organic solvents may include at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone.

[0071] Preferably, the electrolyte of the present invention may include ethylene carbonate and dimethyl carbonate as organic solvents.

[0072] In addition to the electrolyte components mentioned above, the electrolyte may also contain other additives to improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity.

[0073] Representative examples of other additives may include at least one other additive selected from the group consisting of cyclic carbonates, halogenated carbonates, sulfonyl lactones, sulfates or salts, borates or salts, nitriles, benzenes, amines, silanes, and lithium salts that are different from the lithium salts contained in the electrolyte.

[0074] Specifically, other additives may include those selected from vinylene carbonate (VC), vinyl ethylene carbonate, fluoroethylene carbonate (FEC), 1,3-propane sulpholactone (PS), 1,4-butane sulpholactone, vinyl sulpholactone, 1,3-propene sulpholactone (PRS), 1,4-butene sulpholactone, 1-methyl-1,3-propene sulpholactone, ethylene sulfate (Esa), trimethylene sulfate (TMS), methyl trimethylene sulfate (MTMS), tetraphenyl borate, lithium difluoroborate oxalate, succinic anion, adiponitrile, acetonitrile, propionitrile, butyronitrile, valerate, octanoic acid, etc. One or more compounds from the group consisting of nitriles, heptanonitriles, cyclopentonitriles, cyclohexanones, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, fluorobenzene, triethanolamine, ethylenediamine, tetravinylsilane, lithium bis(SO2F)2 (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2 (LiTFSI), LiPO2F2, LiODFB, lithium dioxolaneborate (LiB(C2O4)2 (LiBOB), and LiBF4.

[0075] Based on the total weight of the electrolyte, the content of other additives can be from 0.01 to 20% by weight, preferably from 0.05 to 5.0% by weight. When the amount of other additives is less than 0.01% by weight, the effect of improving the battery's low-temperature output and high-temperature storage and life characteristics may not be significant. When the amount of other additives is greater than 20% by weight, excessive side reactions in the electrolyte may occur during the battery's charge and discharge processes. In particular, when the content of additives used to form the SEI film is excessive, the additives may not decompose sufficiently at high temperatures and may therefore exist in the electrolyte as unreacted substances or precipitates at room temperature. Therefore, side reactions that degrade the life or resistivity characteristics of the secondary battery may occur.

[0076] Electrode assembly

[0077] The electrode assembly of the present invention includes a positive electrode, a negative electrode, and a diaphragm disposed between the positive electrode and the negative electrode.

[0078] Figure 1 The stacked structure of an electrode assembly according to one embodiment of the present invention is shown. Figure 2 The cross-sectional structure of an electrode plate (positive or negative electrode) according to one embodiment of the present invention is shown. Figure 3 The structure of an electrode assembly according to one embodiment of the present invention is shown.

[0079] See Figure 1 and Figure 2 The electrode assembly A of the present invention can be prepared by stacking the diaphragm 12, the positive electrode 10, the diaphragm 12 and the negative electrode 11 at least once in sequence to form a laminate, and then winding the laminate in one direction X.

[0080] At this time, the positive electrode 10 and the negative electrode 11 may each have a structure in which an active material layer 21 is formed on the long sheet-shaped current collector 20, and each may include an uncoated portion 22 in a portion of the current collector 20 in which the active material layer 21 is not formed.

[0081] By using the positive electrode 10 and negative electrode 11, which include the uncoated portion 22 described above, a battery can be provided having a structure that does not include separate electrode tabs and at least a portion of the uncoated portion of each of the positive electrode 10 and negative electrode 11 defines the electrode tabs.

[0082] Specifically, the uncoated portion 22 can be formed longer along the winding direction X at one end of the current collector 20. The current collector plate can be joined to the positive uncoated portion and the negative uncoated portion respectively, and the current collector plate can be connected to the electrode terminal. Therefore, the uncoated portion can function as an electrode tab.

[0083] For example, a battery with uncoated positive and negative electrodes as electrode tabs can be fabricated using the following method. First, a separator, a positive electrode, another separator, and a negative electrode are sequentially stacked such that the uncoated positive and negative electrodes are positioned in opposite directions. Then, the laminate is wound in one direction to form a jelly-roll-type electrode assembly. Subsequently, the uncoated positive and negative electrodes are bent towards the winding center C. A current collector is then welded to each of the uncoated positive and negative electrodes and connected to the electrode terminals to fabricate the battery. The unit area of ​​the current collector can be larger than that of a strip-shaped electrode tab, and the resistance can be inversely proportional to the unit area of ​​the current flow path. Therefore, in the case of a secondary battery with the above structure, the cell resistance can be significantly reduced.

[0084] Meanwhile, the uncoated portions of the positive and negative electrodes can each be processed into multiple segmented pieces that can be bent independently, and at least a portion of the multiple segmented pieces can be bent toward the winding center C of the electrode assembly.

[0085] The segmented sheet can be formed by processing the positive and negative current collectors through metal foil cutting processes such as laser grooving, ultrasonic cutting, and punching.

[0086] When the uncoated portions of the positive and negative electrodes are processed into multiple segmented pieces, the stress applied to the uncoated portions during bending can be reduced, thereby preventing deformation or damage to the uncoated portions and improving the welding characteristics with the current collector.

[0087] The current collector and the uncoated portion are typically joined by welding. To improve welding characteristics, strong pressure needs to be applied to the welding area of ​​the uncoated portion to bend it as flatly as possible. However, during this bending process, the shape of the uncoated portion may irregularly twist and deform, and the deformed part may come into contact with the electrode of opposite polarity, resulting in internal short circuits or micro-cracks in the uncoated portion. However, if the uncoated portions of the positive and negative electrodes are processed into multiple segmented pieces that can be bent independently, the stress applied to the uncoated portion during bending can be reduced, thereby minimizing deformation and damage to the uncoated portion.

[0088] Furthermore, when the uncoated portion is processed into the form of the aforementioned segmented pieces, the multiple segmented pieces can overlap during bending, thus increasing the welding strength with the current collector. Moreover, when using modern technologies such as laser welding, it prevents the laser from penetrating into the electrode assembly and melting the diaphragm or active material. Preferably, at least a portion of the bent multiple segmented pieces can overlap each other on the upper and lower sides of the electrode assembly, and the current collector can be bonded to the overlapping multiple segmented pieces.

[0089] At the same time, such as Figure 3 As shown, the electrode assembly of the present invention can be formed with an insulating layer 24 also formed on the positive electrode 10. Specifically, the insulating layer 24 can be formed in a direction parallel to the winding direction of the electrode assembly to cover a portion of the positive electrode active material layer and a portion of the uncoated portion.

[0090] In the case of a tabless structure battery using the uncoated portion 22c of the positive electrode 10 and the uncoated portion 22a of the negative electrode 11 as electrode tabs, the electrode assembly is formed such that the positive electrode 10 protrudes from the upper part of the separator 12 and the negative electrode 11 protrudes from the lower part of the separator 12, and the protruding positive electrode 10 and / or negative electrode 11 is bent and then joined to the current collector. However, with the positive electrode 10 or negative electrode 11 bent as described above, the current collector of the positive electrode 10 or negative electrode 11 can be configured to cross the separator and be close to the electrode of opposite polarity; therefore, there is a possibility that the positive and negative electrodes may come into electrical contact with each other, causing an internal short circuit. However, as... Figure 5 As shown, when an insulating layer 24 is formed covering the positive electrode active material layer and a portion of the uncoated portion, electrical contact between the positive electrode 10 and the negative electrode 11 can be prevented through the insulating layer 24, thereby preventing a short circuit inside the battery.

[0091] Preferably, the insulating layer 24 may be included on at least one side of the current collector of the positive electrode 10, and preferably on both sides of the positive electrode 10.

[0092] Alternatively, the insulating layer 24 can be formed in the region of the active material layer 21a of the positive electrode 10 that may face the negative electrode 11. For example, the insulating layer 24 can be formed by extending the uncoated portion 22c of the positive electrode 10 to the end of the uncoated portion 22c on the bent surface facing the negative electrode 11. However, in the case of the opposite surface to the bent surface facing the negative electrode 11, it is preferable that the insulating layer 24 is formed only to a portion of the uncoated portion 22c, for example, to the bend point of the uncoated portion 22c. This is because if the insulating layer 24 is formed over the entire region of the uncoated portion on the opposite surface to the surface facing the negative electrode 11, it cannot make electrical contact with the current collector, and the uncoated portion may not be able to function as an electrode tab.

[0093] Meanwhile, there are no particular limitations on the material or composition of the insulating layer 24, as long as it ensures insulation performance and can be adhered to the positive electrode. For example, the insulating layer can be an insulating coating or an insulating tape, and the insulating coating can include organic adhesives and inorganic particles. In this case, the organic adhesive can be, for example, styrene-butadiene rubber (SBR), and the inorganic particles can be alumina, but examples are not limited to these.

[0094] The components of the electrode assembly of the present invention will be described in more detail below.

[0095] positive electrode

[0096] The positive electrode can be prepared by coating one or both sides of a long sheet-shaped positive current collector with a positive electrode slurry, removing the solvent from the positive electrode slurry through a drying process, and then calendering. Meanwhile, a positive electrode including an uncoated portion can be prepared by not coating a portion of the positive current collector (e.g., one end of the positive current collector) with the positive electrode slurry during the coating process.

[0097] Meanwhile, various positive current collectors used in related fields can be used as the positive current collector. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc., can be used. The thickness of the positive current collector can typically range from 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive current collector to improve the adhesion of the positive active material. The positive current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0098] Alternatively, positive electrode slurry can be prepared by dispersing the positive electrode active material in solvents such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water.

[0099] For the positive electrode active material, commonly used positive electrode active materials in the relevant field can be used, and there are no particular restrictions on the type.

[0100] Preferably, the positive electrode active material may include lithium transition metal oxides containing Ni and Co, and more preferably, it may include lithium nickel oxides represented by the following chemical formula 1.

[0101] [Chemical Formula 1]

[0102] Li a Ni b Co c M 1 d M 2 e O2

[0103] In the above chemical formula 1, M 1 It can be Mn, Al or a combination thereof, with Mn or Mn and Al being preferred.

[0104] The above M 2 It can be one or more elements selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb. It does not necessarily include element M. 2 However, if included in appropriate amounts, it can promote particle growth or improve the stability of the crystal structure during the firing process.

[0105] The above-mentioned a represents the molar ratio of lithium in the lithium nickel-based oxide, where 0.8 ≤ a ≤ 1.2, 0.85 ≤ a ≤ 1.15, or 0.9 ≤ a ≤ 1.2 can be satisfied. When the molar ratio of lithium is within the above range, the crystal structure of the lithium nickel-based oxide can be formed stably.

[0106] The above-mentioned b represents the molar ratio of nickel in all metals other than lithium in the lithium nickel-based oxide, where 0.50 < b < 1, 0.60 ≤ b < 1, 0.80 ≤ b < 1, 0.85 ≤ b < 1, or 0.90 ≤ b < 1 can be satisfied.

[0107] The above-mentioned c represents the molar ratio of cobalt in all metals other than lithium in the lithium nickel-based oxide, where 0 < c < 0.50, 0 < c < 0.40, 0 < c < 0.20, 0 < c < 0.15, or 0 < c < 0.10 can be satisfied. When the molar ratio of cobalt is within the above range, good resistance characteristics and output characteristics can be obtained.

[0108] The above-mentioned d represents the molar ratio of the M 1 element in all metals other than lithium in the lithium nickel-based oxide, where 0 < d < 0.50, 0 < d < 0.40, 0 < d < 0.20, 0 < d < 0.15, or 0 < d < 0.10 can be satisfied. When the molar ratio of the M 1 element is within the above range, the structural stability of the positive electrode active material is excellent.

[0109] The above-mentioned e represents the molar ratio of the M 2 element in all metals other than lithium in the lithium nickel-based oxide, where 0 ≤ e ≤ 0.1 or 0 ≤ e ≤ 0.05 can be satisfied.

[0110] Specifically, the lithium nickel-based oxide can be Li(Ni 0.60 Co 0.10 Mn 0.30 )O2, Li(Ni 0.60 Co 0.20 Mn 0.20 )O2, Li(Ni 0.80 Co 0.10 Mn 0.10 )O2, Li(Ni 0.90 Mn 0.05 Co 0.05 )O2, Li(Ni 0.94 Co 0.04 Mn 0.02 )O2, Li(Ni 0.87 Mn 0.07 Co 0.04 Al 0.02 )O2 or Li(Ni <​​0.05 Al 0.02 O2, etc., but examples are not limited to these.

[0111] Additionally, the positive electrode slurry may optionally also include at least one of a conductive material and a binder.

[0112] Conductive materials are used to provide conductivity to the electrodes. Any material that does not cause chemical changes and conducts electrons can be used in the battery without particular limitations. Specific examples include: graphite, such as natural or artificial graphite; carbon materials, including carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fiber, carbon nanotubes, etc.; powders or fibers of metals including copper, nickel, aluminum, silver, etc.; conductive whiskers, including zinc oxide, potassium titanate, etc.; conductive metal oxides, including titanium oxide, etc.; or conductive polymers, including polyphenylene derivatives, etc., and any one or a mixture of two or more of these can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material can be from 1% to 30% by weight, preferably from 1% to 20% by weight, more preferably from 1% to 10% by weight.

[0113] Adhesives can be 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 include: fluoropolymer adhesives including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber adhesives including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose adhesives including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyol adhesives including polyvinyl alcohol; polyolefin adhesives including polyethylene and polypropylene; polyimide adhesives; polyester adhesives; and silane adhesives, which may be used individually or in mixtures of two or more of these. Based on the total weight of the positive electrode active material layer, the adhesive content may be 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0114] negative electrode

[0115] The negative electrode can be prepared by coating one or both sides of a long sheet-shaped negative electrode current collector with a negative electrode slurry, removing the solvent from the negative electrode slurry through a drying process, and then calendering. Meanwhile, a negative electrode including an uncoated portion can be prepared by leaving a portion of the negative electrode current collector (e.g., one end of the negative electrode current collector) uncoated during the coating process.

[0116] Meanwhile, as the negative electrode current collector, those commonly used in the relevant field can be used. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface-treated with carbon, nickel, titanium or silver, aluminum-cadmium alloy, etc. can be used. The thickness of the negative electrode current collector can usually be 3 to 500 μm, and similar to the positive electrode current collector, fine concavities and convexities can be formed on the surface of the current collector to improve the bonding force of the negative electrode active material. For example, the current collector can be used in various forms, including films, sheets, foils, meshes, porous bodies, foams, non-woven fabric bodies, etc.

[0117] In addition, the negative electrode slurry can be prepared by dispersing the negative electrode active material in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or water.

[0118] As the negative electrode active material, carbon-based negative electrode active materials used in the relevant field can be used. In addition, silicon-based negative electrode active materials can be mixed in the carbon-based negative electrode active materials.

[0119] For carbon-based active materials, various carbon-based active materials used in the relevant field can be used. For example, graphite-based materials such as natural graphite, artificial graphite and Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fibers, mesocarbon microbeads, mesophase pitch, and high-temperature fired carbon such as petroleum or coal tar pitch-derived coke, soft carbon, hard carbon, etc. The shape of the carbon-based materials is not particularly limited, and materials with various shapes such as amorphous, plate-shaped, flaky, spherical or fibrous can be used.

[0120] In addition, the silicon-based negative electrode active material can include one or more selected from the group consisting of, for example, silicon (Si), silicon carbide (SiC), silicon chloride, silicon oxide (SiO x , where 0 < x < 2), and Si-Y alloy (where Y is selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements and combinations thereof, and is not Si). The element Y can be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po and combinations thereof.

[0121] Meanwhile, the weight ratio of the included carbon-based negative electrode active material to the silicon-based negative electrode active material can be 99:1 to 95:10, preferably the weight ratio is 99:1 to 95:5, and more preferably the weight ratio is 97:3 to 95:5.

[0122] When the mixing ratio of carbon-based anode active materials to silicon-based anode active materials is within the above range, the volume expansion of silicon compounds can be suppressed while improving capacity characteristics, thus ensuring excellent cycle performance. If there is too little silicon (Si) compounds, it is difficult to increase energy density, making it difficult to achieve high battery capacity; if there is too much, the volume expansion of the anode may increase, which is undesirable.

[0123] Additionally, the negative electrode paste may optionally also include at least one of a conductive material and a binder.

[0124] Conductive materials are used to provide conductivity to the negative electrode. Any material that does not cause a chemical change and conducts electrons can be used in the battery without particular limitations. Specific examples include: graphite, such as natural or artificial graphite; carbon materials, including carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fiber, carbon nanotubes, etc.; powders or fibers of metals including copper, nickel, aluminum, silver, etc.; conductive whiskers, including zinc oxide, potassium titanate, etc.; conductive metal oxides, including titanium oxide, etc.; or conductive polymers, including polyphenylene derivatives, etc. Any one or a mixture of two or more of these can be used. Based on the total weight of the negative electrode active material layer, the content of the conductive material can be from 1% to 30% by weight, preferably from 1% to 20% by weight, more preferably from 1% to 10% by weight.

[0125] 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 can be: fluoropolymer adhesives including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber adhesives including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose adhesives including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyol adhesives including polyvinyl alcohol; polyolefin adhesives including polyethylene and polypropylene; polyimide adhesives; polyester adhesives; and silane adhesives, which may be used individually or in mixtures of two or more of these. Based on the total weight of the negative electrode active material layer, the adhesive content can be 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0126] diaphragm

[0127] The separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is used as a separator in a general lithium secondary battery. Specifically, porous polymer membranes can be used as separators, such as porous polymer membranes prepared from polyolefin polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or laminated structures of two or more layers can be used. Alternatively, general porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, coated separators including ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength.

[0128] Lithium secondary batteries

[0129] The lithium secondary battery of the present invention will be described below.

[0130] Figure 4 and Figure 5 An embodiment of the lithium secondary battery of the present invention is shown. In the following, reference is made to... Figure 4 and Figure 5 The lithium secondary battery of the present invention will be described below. However, Figure 4 and Figure 5 Only one embodiment of the present invention has been shown, and the structure of the battery of the present invention is not limited to this. Figure 4 and Figure 5 The range shown.

[0131] Figure 4 A cross-sectional view of a tabless structure lithium secondary battery according to one embodiment of the present invention is shown.

[0132] See Figure 4 The lithium secondary battery 140 of the present invention includes an electrode assembly 141, a battery housing 142 that houses the electrode assembly 141 and an electrolyte (not shown), and a sealing body 143 that seals the open end of the battery housing 142.

[0133] At this point, the electrode assembly can be formed by winding a laminate of the positive electrode, separator, and negative electrode in one direction. Furthermore, the positive and negative electrodes of the electrode assembly may each include an uncoated portion without an active material layer, and the electrode assembly can be stacked and wound such that the uncoated portions of the positive and negative electrodes are respectively located at the upper and lower ends of the electrode assembly. Since the electrode assembly has already been described, only components other than the electrode assembly will be described below.

[0134] Meanwhile, the battery casing 142 is a can-shaped container with an open end formed on the upper side, and is made of a conductive metallic material, such as aluminum or steel. The battery casing houses the electrode assembly 141 in the internal space through the open end on the upper side, and also houses the electrolyte (not shown).

[0135] Furthermore, the lithium secondary battery 140 of the present invention preferably does not include a current interruption device (CID).

[0136] At the same time, such as Figure 4 As shown, the battery casing 142 can be electrically connected to the uncoated portion 146b of the negative electrode and can contact an external power source to act as a negative terminal that transmits current applied from the external power source to the negative electrode.

[0137] If necessary, a rolled edge portion 147 and a crimped portion 148 may be included on the upper side of the battery housing 142. The rolled edge portion 147 can be formed by pressing the outer peripheral surface of the battery housing 142 in until a distance D1 is reached. The rolled edge portion 147 can prevent the electrode assembly 141 housed inside the battery housing 142 from escaping through the upper opening of the battery housing 142, and can also serve as a support for placing the sealing body 143.

[0138] The crimping portion 148 may be formed above the rolled edge portion 147 and has an extended and curved shape to surround the outer peripheral surface of the cover plate 143a disposed on the rolled edge portion 147 and a portion of the upper surface of the cover plate 143a.

[0139] Next, the sealing body 143 seals the open end of the battery housing 142 and includes a cover plate 143a and a first gasket 143b. The first gasket 143b provides airtightness and insulation between the cover plate 143a and the battery housing 142. If necessary, the sealing body may further include a connecting plate 143c that is electrically and mechanically connected to the cover plate 143a. The cover plate 143a can be pressed onto the rolled edge 147 formed on the battery housing 142 and can be fixed by a crimping portion 148.

[0140] The cover plate 143a is a component formed of a conductive metallic material and covers the upper opening of the battery casing 142. The cover plate 143a is electrically connected to the positive terminal of the electrode assembly 141 and is electrically insulated from the battery casing 142 by a first gasket 143b. Therefore, the cover plate 143a can serve as the positive terminal of a lithium secondary battery. The cover plate 143a may include a protrusion 143d extending upward from the center C, and the protrusion 143d can contact an external power source, allowing current to be applied from the external power source.

[0141] The first gasket 143b can be disposed between the cover plate 143a and the crimping part 148 to ensure the airtightness of the battery housing 142 and the electrical insulation between the battery housing 142 and the cover plate 143a.

[0142] Additionally, if necessary, the lithium secondary battery 140 of the present invention may also include current collectors 144 and 145. The current collectors are respectively coupled to the uncoated portion 146a of the positive electrode and the uncoated portion 146b of the negative electrode, and connected to the electrode terminals (i.e., the positive terminal and the negative terminal).

[0143] Specifically, the cylindrical battery 140 of the present invention may include a first current collector 144 attached to the upper part of the electrode assembly 141 and a second current collector 145 attached to the lower part of the electrode assembly 141.

[0144] It may also include a first collector plate 144 and / or a second collector plate 145.

[0145] A first current collector 144 is joined to the upper part of the electrode assembly 141. The first current collector 144 is made of a conductive metal material such as aluminum, copper, or nickel, and is electrically connected to the uncoated portion 146a of the positive electrode. A lead 149 can be connected to the first current collector 144. The lead 149 can extend upward from the electrode assembly 141 to join to the connecting plate 143c, or it can be directly joined to the lower surface of the cover plate 143a. The joining of the lead 149 to other components can be achieved by welding. Preferably, the first current collector 144 can be integrally formed with the lead 149. In this case, the lead 149 can have a plate-like shape extending outward from the center of the first current collector 144.

[0146] Meanwhile, the first current collector 144 can be joined to the end of the uncoated portion 146a of the positive electrode, and the joining can be performed by methods such as laser welding, resistance welding, ultrasonic welding and brazing.

[0147] The second current collector 145 is joined to the lower part of the electrode assembly 141. The second current collector 145 is made of a conductive metal material such as aluminum, copper, and nickel, and is electrically connected to the uncoated portion 146b of the negative electrode. One side of the second current collector 145 can be joined to the uncoated portion 146b of the negative electrode, and the opposite side can be joined to the inner bottom surface of the battery casing 142. The joining can be performed by methods including laser welding, resistance welding, ultrasonic welding, brazing, etc.

[0148] Additionally, if necessary, the lithium secondary battery 140 of the present invention may further include an insulator 146. The insulator 146 may be configured to cover the upper side of the first current collector 144. Since the insulator 146 covers the first current collector 144, direct contact between the first current collector 144 and the inner periphery of the battery casing 142 can be prevented.

[0149] The insulator 146 includes a lead hole 151, through which a lead 149 extending upward from the first current collector 144 can be pulled out. The lead 149 is pulled out upward through the lead hole 151 and engages with the lower surface of the connecting plate 143c or the lower surface of the cover plate 143a.

[0150] Insulator 146 may be made of insulating polymer resin (e.g., polymer resin materials such as polyethylene, polypropylene, polyimide or polybutylene terephthalate).

[0151] Additionally, if necessary, the lithium secondary battery 140 of the present invention may further include an venting portion 152 formed on the lower surface of the battery casing 142. The venting portion 152 corresponds to a region on the lower surface of the battery casing 142 that has a smaller thickness compared to the surrounding region. Due to its smaller thickness, the venting portion 152 is structurally more fragile compared to the surrounding region. Therefore, when the pressure inside the lithium secondary battery 140 rises above a certain level, the venting portion 152 ruptures and the gas inside the battery casing 152 is released to the outside, thereby preventing the battery from exploding.

[0152] Figure 5 A cross-sectional view of a tabless structure lithium secondary battery according to another embodiment of the present invention is shown.

[0153] See Figure 5 In another embodiment of the present invention, the lithium secondary battery 170 has the same characteristics as... Figure 4 The lithium secondary battery 140 shown has different battery casing and sealing structures, and the electrode assembly and electrolyte configurations are different. Figure 4 Basically the same.

[0154] Specifically, according to another embodiment of the present invention, a lithium secondary battery 170 includes a battery housing 171 through which a rivet terminal 172 is mounted. The rivet terminal 172 is mounted on a partially closed closed surface (the upper surface in the figure) at one end of the battery housing 171. The rivet terminal 172 is riveted through a through hole (the first opening at the first end) of the battery housing 171 with an insulating second washer 173 provided. The rivet terminal 172 protrudes to the outside in the direction opposite to the direction of gravity.

[0155] The rivet terminal 172 includes a terminal protrusion 172a and a terminal insertion portion 172b. The terminal protrusion 172a protrudes to the outside of the closed surface of the battery housing 171. The terminal protrusion 172a may be located approximately at the center of a portion of the closed surface of the battery housing 171. The maximum diameter of the terminal protrusion 172a may be larger than the maximum diameter of the through hole formed in the battery housing 171. The terminal insertion portion 172b may pass through approximately the center of the closed surface of the battery housing 171, thereby enabling electrical connection to the uncoated portion 146a of the positive electrode. The terminal insertion portion 172b may be riveted to the inner surface of the battery housing 171. That is, the end of the terminal insertion portion 172b may have a shape that bends toward the inner surface of the battery housing 171. The maximum diameter of the end of the terminal insertion portion 172b may be larger than the maximum diameter of the through hole in the battery housing 171.

[0156] The lower end surface of the terminal insertion portion 172b can be welded to the first current collector 144, which is connected to the uncoated portion 146a of the positive electrode. An insulating cap 174, made of insulating material, can be disposed between the first current collector 144 and the inner surface of the battery casing 171. The insulating cap 174 covers the upper part of the first current collector 144 and the upper edge of the electrode assembly 141. Therefore, it can prevent the uncoated portion B3 of the outer periphery of the electrode assembly 141 from contacting the inner surface of the battery casing 171, which has a different polarity, thus preventing a short circuit. The terminal insertion portion 172b of the rivet terminal 172 can pass through the insulating cap 174 to be welded to the first current collector 144.

[0157] A second washer 173 is disposed between the battery casing 171 and the rivet terminal 172 to prevent the battery casing 171 and the rivet terminal 172 from making electrical contact, despite their opposite polarities. Therefore, the upper surface of the battery casing 171, which has a generally flat shape, can be used as the positive terminal of the lithium secondary battery 170.

[0158] The second washer 173 includes a washer protrusion 173a and a washer insertion portion 173b. The washer protrusion 173a is disposed between the terminal protrusion 172a of the rivet terminal 172 and the battery housing 171. The washer insertion portion 173b is disposed between the terminal insertion portion 172b of the rivet terminal 172 and the battery housing 171. The washer insertion portion 173b can deform together with the terminal insertion portion 172b during riveting, thereby allowing it to adhere tightly to the inner surface of the battery housing 171. The second washer 173 can be made of, for example, an insulating polymer resin.

[0159] The washer protrusion 173a of the second washer 173 may have an extended shape to cover the outer periphery of the terminal protrusion 172a of the rivet terminal 172. With the second washer 173 covering the outer periphery of the rivet terminal 172, short circuits can be prevented during the connection of electrical connection components such as busbars to the upper surface of the battery housing 171 and / or the rivet terminal 172. Although not shown in the figures, the washer protrusion 173a may have an extended shape to cover not only the outer periphery of the terminal protrusion 172a but also a portion of its upper surface.

[0160] When the second washer 173 is made of polymer resin, it can be heat-fused to the battery housing 171 and the rivet terminal 172. This enhances the airtightness at the interface between the second washer 173 and the rivet terminal 172, as well as at the interface between the second washer 173 and the battery housing 171. Furthermore, when the washer protrusion 173a of the second washer 173 has a shape extending to the upper surface of the terminal protrusion 172a, the rivet terminal 172 can be integrally bonded to the second washer 173 via injection molding.

[0161] The remaining area 175 of the upper surface of the battery casing 171, excluding the area occupied by the rivet terminal 172 and the second washer 173, corresponds to the negative terminal with the opposite polarity to the rivet terminal 172.

[0162] The second current collector 176 is attached to the lower part of the electrode assembly 141. The second current collector 176 is made of a conductive metal material such as aluminum, copper and nickel, and is electrically connected to the uncoated portion 146b of the negative electrode.

[0163] Preferably, the second current collector 176 is electrically connected to the battery housing 171. For this purpose, at least a portion of the edge of the second current collector 176 can be disposed and fixed between the inner surface of the battery housing 171 and the first gasket 178b. In one embodiment, at least a portion of the edge of the second current collector 176 can be fixed to the rolled edge 180 by welding while supported by the lower surface of the rolled edge 180 formed on the lower side of the battery housing 171. In other embodiments, at least a portion of the edge of the second current collector 176 can be directly welded to the inner wall of the battery housing 171.

[0164] The second manifold 176 may include a plurality of irregularities (not shown) formed in all directions on the surface opposite to the uncoated portion 146b. When irregularities are formed, they can be pressed onto the uncoated portion 146b by pressing the second manifold 176.

[0165] Preferably, the ends of the second manifold 176 and the uncoated portion 146b can be joined by welding, for example, laser welding.

[0166] The sealing body 178 at the lower opening end of the sealed battery housing 171 includes a cover plate 178a and a first washer 178b. The first washer 178b electrically separates the cover plate 178a and the battery housing 171. A crimping portion 181 secures the edge of the cover plate 178a and the first washer 178b together. The cover plate 178a includes a venting portion 179. The configuration of the venting portion 179 is substantially the same as in the aforementioned embodiment.

[0167] Preferably, the cover plate 178a is made of a conductive metal material. However, since the first gasket 178b is disposed between the cover plate 178a and the battery casing 171, the cover plate 178a is not polarized. The sealing body 178 seals the lower opening of the battery casing 171, and when the internal pressure of the battery cell 170 rises above a critical value, the sealing body 178 serves to release gas.

[0168] Preferably, the rivet terminal 172, electrically connected to the uncoated portion 146a of the positive electrode, serves as the positive terminal. Additionally, the portion 175, excluding the rivet terminal 172, on the upper surface of the battery casing 171, which is electrically connected to the uncoated portion 146b of the negative electrode via the second current collector 176, serves as the negative terminal. Therefore, when both electrode terminals are located at the top of the lithium secondary battery, electrical connection components such as busbars can be provided only on one side of the lithium secondary battery 170. This leads to a simplification of the battery pack structure and an increase in energy density. Furthermore, since the portion 175 serving as the negative terminal has a substantially flat shape, sufficient contact area can be ensured when joining electrical connection components such as busbars. Therefore, in the lithium secondary battery 170, the resistance of the contact portion can be reduced to a desired level.

[0169] When a lithium secondary battery is formed using the aforementioned tabless structure, compared to a conventional battery containing electrode tabs, the current concentration of the lithium secondary battery can be reduced, thereby effectively reducing the heat inside the battery and thus improving the thermal safety of the battery.

[0170] Meanwhile, the lithium secondary battery of the present invention can be a cylindrical battery. Preferably, the cylindrical lithium secondary battery of the present invention can be a large cylindrical battery with a shape factor ratio (defined as the value obtained by dividing the diameter of the cylindrical battery by its height, i.e., the ratio of diameter (T) to height (H)) of 0.4 or more, preferably 0.4 to 0.6. Here, the shape factor refers to the value representing the diameter and height of the cylindrical battery.

[0171] The cylindrical battery of the present invention can be, for example, a 46110 cell (diameter 46 mm, height 110 mm, shape factor ratio 0.418), a 48110 cell (diameter 48 mm, height 110 mm, shape factor ratio 0.436), a 4880 cell (diameter 48 mm, height 80 mm, shape factor ratio 0.600), or a 4680 cell (diameter 46 mm, height 80 mm, shape factor ratio 0.575). In the shape factor values, the first two digits represent the diameter of the cell, and the next two or three digits represent the height of the cell.

[0172] The lithium secondary battery of the present invention described above can be used as a unit cell in the preparation of a battery pack. Figure 6 The schematic illustration shows the configuration of a battery pack according to an embodiment of the present invention. See also Figure 6 The battery pack 3 of this embodiment includes a component that electrically connects to the lithium secondary battery 1 and a battery pack housing 2 that houses the component. The lithium secondary battery 1 is the lithium secondary battery of the aforementioned embodiment. In the figures, for ease of illustration, the busbars, cooling units, and external terminals used for electrically connecting to the lithium secondary battery 1 are omitted from the illustration.

[0173] Battery pack 3 can be installed in a vehicle. For example, the vehicle can be an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle. The vehicle can be a four-wheeled vehicle or a two-wheeled vehicle.

[0174] The present invention will be described in more detail below through specific embodiments.

[0175] Examples 1 to 2 and Comparative Examples 1 to 4

[0176] <Preparation of Electrolytes>

[0177] LiPF6 was placed in an organic solvent containing ethylene carbonate such that the molar amount of ethylene carbonate in the electrolyte (M) was [missing information]. EC ), number of moles of LiPF6 (M) LiPF6 ) and the number of moles of organic solvent (M) solvent Mix the amounts of substances that meet the molar numbers listed in Table 1 below to prepare the electrolyte.

[0178] <Preparation of Electrode Components>

[0179] A positive electrode slurry was prepared by adding a positive electrode active material, a conductive material, and a binder to N-methylpyrrolidone in a weight ratio of 97.5:1.0:1.5. Li[Ni] was used as the positive electrode active material. 0.93 Co 0.05 Mn 0.02 O2 is used as a conductive material, carbon nanotubes are used, and PVDF is used as a binder.

[0180] The positive electrode slurry is coated onto an aluminum current collector, dried, and then rolled to prepare the positive electrode.

[0181] A negative electrode slurry was prepared by adding the negative electrode active material, conductive material, and binder to distilled water in a weight ratio of 95.0:3.5:1.5. Graphite was used as the negative electrode active material, acetylene black as the conductive material, and a mixture of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as the binder.

[0182] The negative electrode slurry is coated onto a copper current collector, dried, and then rolled to prepare the negative electrode.

[0183] A separator is placed between the positive and negative electrodes prepared above, and the layers are stacked in the order of separator / positive electrode / separator / negative electrode. The laminate is then wound to prepare a jelly roll electrode assembly.

[0184] <Preparation of Lithium Secondary Batteries>

[0185] The electrode assembly was inserted into a cylindrical battery canister with a diameter of 46 mm and a height of 80 mm. Then, the electrolyte prepared above was injected in the amounts listed in Table 1 below to prepare a 4680 cell, which was then formed to prepare a lithium secondary battery.

[0186] The number of moles of ethylene carbonate in the electrolytes of the respective examples and comparative examples (M) EC ), number of moles of LiPF6 (M) LiPF6 ) and the number of moles of organic solvent (M) solvent The E values ​​of (2) and mathematical formula (2) are listed in Table 1 below.

[0187] [Table 1]

[0188] Experimental Example 1: Gas Composition

[0189] The lithium secondary batteries prepared as described above in the examples and comparative examples were each charged and discharged at voltage ranges of 0.33C and 2.5V to 4.2V to measure the discharge capacity C.

[0190] Furthermore, after the formation process is complete, the battery casing is punched in a vacuum atmosphere chamber to release the gas inside the battery and collect the gas into the vacuum chamber. The composition of the collected gas is analyzed using gas chromatography-flame ionization detector (GC-FID) to measure (V0). CH - V CO ) / V total The value of .

[0191] Subsequently, the measured discharge capacity C and (V) CH - V CO ) / Vtotal Substitute into mathematical formula (1) to calculate the value of G. The measurement results are listed in Table 2 below.

[0192] [Table 2]

[0193] Experiment Example 2: Battery Performance Evaluation

[0194] The initial resistance, initial energy, and capacity retention after 100 cycles of each lithium secondary battery prepared in the Examples and Comparative Examples are evaluated below. The evaluation results are listed in Table 3.

[0195] (1) Initial DCIR: The lithium secondary battery was charged to SOC 50 at 0.33C and then discharged at 0.5C for 10 seconds at room temperature to measure the voltage change ΔV. The measured voltage change ΔV was divided by the current I to calculate the initial DCIR (R=ΔV / I). Based on the initial DCIR value (100%) of the lithium secondary battery of Comparative Example 1, the relative values ​​of the initial DCIR of the Example and the Comparative Example are listed in Table 3 below.

[0196] (2) Initial energy: The lithium secondary battery was charged to 4.2V at 40°C and then discharged to 2.5V at 19.1W, and the amount of energy obtained was measured. Based on the amount of initial energy (100%) of the lithium secondary battery of Comparative Example 1, the relative values ​​of the amount of initial energy of the Examples and Comparative Examples are listed in Table 3 below.

[0197] (3) Cycling characteristics: The lithium secondary battery was subjected to 100 charge-discharge cycles, wherein one cycle consisted of charging to 4.2V at 0.5C in constant current and constant voltage mode and then discharging to 2.4V at 0.5C in constant current mode. The capacity retention rate was then measured (capacity after 100 cycles: capacity after 1 cycle). Based on the capacity retention rate (100%) of the lithium secondary battery of Comparative Example 1 after 100 cycles, the relative values ​​of the capacity retention rates of the Examples and Comparative Examples after 100 cycles are listed in Table 3 below.

[0198] [Table 3]

[0199] Referring to Table 3 above, it can be seen that the lithium secondary batteries of Examples 1 and 2, which were designed to have a G value in the range of 1.8 to 3.5, have better initial DCIR, initial energy and cycle characteristics compared with the lithium secondary batteries of Comparative Examples 1, 3 and 4 with a G value less than 1.8 and the lithium secondary battery of Comparative Example 2 with a G value greater than 3.5.

Claims

1. A lithium secondary battery, comprising: Battery casing; and The electrode assembly and electrolyte are housed within the battery casing. in, The electrode assembly includes: positive electrode; Negative electrode; and A diaphragm is disposed between the positive electrode and the negative electrode. The electrolyte contains a lithium salt and an organic solvent, and The value of G, as defined by the following mathematical formula (1), ranges from 1.8 to 3.

5. Mathematical formula (1): In the mathematical formula (1) above, V CH V represents the volume of hydrocarbon gases present in the lithium-ion secondary battery after formation, expressed in mL. CO V represents the volume of carbon oxide gases present in the lithium-ion secondary battery after formation, expressed in mL. total The total volume of gas present in the lithium secondary battery after formation is expressed in mL, and C is the discharge capacity of the lithium secondary battery when charged and discharged at a voltage range of 0.33 C and 2.5 V to 4.2 V.

2. The lithium secondary battery as described in claim 1, wherein, In the mathematical expression (1) above, (V CH - V CO ) / V total The value ranges from 0.40 to 0.

85.

3. The lithium secondary battery as described in claim 1, wherein, The discharge capacity C is 20 Ah to 50 Ah.

4. The lithium secondary battery as described in claim 1, wherein, The lithium salt includes LiPF6, and The organic solvent includes ethylene carbonate.

5. The lithium secondary battery as described in claim 4, wherein, The E value of the lithium secondary battery, as defined by the following mathematical formula (2), is between 14.0 and 17.

5. Mathematical expression (2): In the mathematical formula (2) above, M EC M represents the number of moles of ethylene carbonate in the electrolyte. LiPF6 M represents the number of moles of LiPF6 in the electrolyte. Solvent The total number of moles of the organic solvent in the electrolyte, MW EC A is the molecular weight of ethylene carbonate, A is the solubility constant of LiPF6 in the electrolyte, and C is the discharge capacity of the lithium secondary battery when charged and discharged in a voltage range of 0.33 C and 2.5 V to 4.2 V.

6. The lithium secondary battery as described in claim 5, wherein, The number of moles of ethylene carbonate in the electrolyte, M EC The amount ranges from 0.070 to 0.090 moles.

7. The lithium secondary battery as described in claim 5, wherein, The number of moles of LiPF6 in the electrolyte, M LiPF6 The amount is 0.3 to 0.5 moles.

8. The lithium secondary battery as described in claim 5, wherein, The total molar number M of the organic solvent in the electrolyte Solvent It is 0.3 to 0.4 moles.

9. The lithium secondary battery as described in claim 5, wherein, The solubility constant A of LiPF6 in the electrolyte is 3 to 4.

10. The lithium secondary battery as described in claim 1, wherein, The lithium secondary battery is a cylindrical battery with a diameter (r) to height (h) ratio of the battery casing, i.e., a shape factor ratio of 0.4 or higher.

11. The lithium secondary battery as described in claim 1, wherein, The lithium secondary battery is a 46110 cell, a 48110 cell, a 4880 cell, or a 4680 cell.

12. The lithium secondary battery as described in claim 1, wherein, The lithium secondary battery includes uncoated portions on at least a portion of the positive electrode and the negative electrode where no active material layer is formed, and the uncoated portions of the positive electrode and the negative electrode are each defined as electrode tabs.

13. The lithium secondary battery as described in claim 12, wherein, The uncoated portion of the positive electrode and the uncoated portion of the negative electrode are formed at the ends of the positive electrode and the negative electrode respectively along the winding direction of the electrode assembly. The current collector is engaged with the uncoated portion of the positive electrode and the uncoated portion of the negative electrode respectively, and the current collector is connected to the electrode terminal.

14. The lithium secondary battery as described in claim 12, wherein, The uncoated portions of the positive and negative electrodes are processed into multiple segmented pieces that can be bent independently, and At least a portion of the plurality of segmented pieces bends toward the winding center of the electrode assembly.

15. The lithium secondary battery as described in claim 14, wherein, At least a portion of the multiple curved segments overlap on the upper and lower sides of the electrode assembly, and the current collector is engaged to the overlapping multiple segments.

16. A battery pack comprising a lithium secondary battery as a unit cell according to any one of claims 1 to 15.

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