Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery and a method of manufacturing the same, the lithium secondary battery comprising: an electrode assembly including a cathode, an anode, and a separator disposed between the cathode and the anode; an electrolyte including a lithium salt and an organic solvent; and a battery case accommodating the electrode assembly and the electrolyte, wherein a Y value defined by Mathematical Formula 1 is 0.15 to 0.30.

Description

Technical Field

[0001] This invention relates to a lithium secondary battery, and more specifically to a lithium secondary battery designed to meet specific conditions regarding battery specifications and the gas composition, electrolyte residue, solvent composition, and discharge capacity of the formed secondary battery. Background Technology

[0002] With the technological advancements in electric vehicles and portable electronic devices, the demand for lithium-ion batteries as an energy source has increased significantly.

[0003] Based on the shape of the battery casing, lithium secondary batteries can be classified into cylindrical, prismatic, and pouch batteries. A cylindrical battery is formed by housing a jelly-roll-shaped electrode assembly—made by sequentially stacking and winding sheet-like positive electrodes, a separator, and a negative electrode in one direction—within a cylindrical battery casing, and then sealing the top of the casing with a cover plate. The positive and negative electrodes each have strip-shaped positive and negative tabs, which are connected to electrode terminals for electrical connection to an external power source. For reference, the positive terminal is the cover plate, and the negative terminal is the battery casing.

[0004] Traditionally, small cylindrical secondary batteries with shape factors of 1865 (18 mm in diameter × 65 mm in height) or 2170 (21 mm in diameter × 70 mm in height) have been mainly used. However, in recent years, with the requirement for electric vehicles to have increased driving range and faster charging rates, the development and use of large cylindrical secondary batteries with larger shape factors, such as 4680 (46 mm in diameter × 80 mm in height), are being considered.

[0005] Because large cylindrical secondary batteries have a large capacity, the following problems exist: when using strip-shaped electrode tabs as in traditional small cylindrical secondary batteries, the current concentrated on the electrode tabs increases, thereby increasing resistance and heat generation, and reducing current collection efficiency. Therefore, a so-called tablessless cylindrical secondary battery has been proposed, in which the uncoated current collectors of the positive and negative electrodes themselves are used as electrode tabs, instead of using separate strip-shaped electrode tabs.

[0006] Cylindrical secondary batteries with tabless structures not only exhibit relatively large capacity characteristics and energy density, but also have the advantages of improving the production efficiency and reducing the unit cost of cylindrical secondary batteries for electric vehicles. Furthermore, the tabless structure reduces the number of parts while increasing the electrical connection (contact) area between the electrode tabs and terminals, reducing the electron travel distance, thus improving output characteristics and dissipating heat generated during charging and discharging.

[0007] However, for large cylindrical secondary batteries employing tabless structures, the process of pressurizing the uncoated active material layers to ensure sufficient weldability to the casing and terminals obstructs the electrolyte movement path between the positive, separator, and negative electrodes in the wound electrode assembly. This hinders proper electrolyte movement, reducing electrolyte wettability and consequently altering the composition of the solid electrolyte interphase (SEI) layer formed during formation. Furthermore, it increases the decomposition of the electrolyte solvent during battery operation. Therefore, applying the same electrolyte system as conventional small cylindrical secondary batteries to large cylindrical secondary batteries makes it difficult to achieve the desired electrochemical performance.

[0008] Therefore, there is a need to develop a technology that can achieve excellent electrochemical performance in large cylindrical secondary batteries suitable for medium and large-sized devices such as automobiles. Summary of the Invention

[0009] Technical issues

[0010] One aspect of the present invention provides a lithium secondary battery that can achieve excellent electrochemical performance by being designed to meet specific conditions regarding battery specifications and the gas composition, electrolyte residue, solvent composition, and discharge capacity of the formed secondary battery.

[0011] Technical solution

[0012] [1] The present invention provides a lithium secondary battery, comprising: an electrode assembly including a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode; an electrolyte comprising a lithium salt and an organic solvent; and a battery casing accommodating the electrode assembly and the electrolyte. The organic solvent comprises dimethyl carbonate, and The value of Y, as defined by mathematical formula 1, ranges from 0.15 to 0.30.

[0013] [Mathematical Expression 1]

[0014] In mathematical formula 1, FF is the ratio of the diameter to the height of the battery casing. E is the amount of electrolyte residue measured in grams. r DMC It is the weight ratio of dimethyl carbonate to the total weight of the solvent in the electrolyte. V CH4 The volume of CH4 gas present in the lithium secondary battery is measured in mL, and C is the discharge capacity of the lithium secondary battery, measured in Ah, when charged and discharged at 0.5 C within the range of 2.5 V to 4.2 V. Where Y is a dimensionless number.

[0015] [2] The present invention provides the lithium secondary battery described in [1] above, wherein the ratio of the volume of the CH4 gas to the total volume of the gas present in the lithium secondary battery is 0.40 to 0.80.

[0016] [3] The present invention provides a lithium secondary battery as described in [1] or [2] above, wherein the residual amount of electrolyte is 25 g to 32 g.

[0017] [4] The present invention provides a lithium secondary battery according to at least one of [1] to [3] above, wherein the discharge capacity is 10 Ah to 50 Ah when the lithium secondary battery is charged and discharged at 0.5 C in the range of 2.5 V to 4.2 V.

[0018] [5] The present invention provides a lithium secondary battery according to at least one of [1] to [4] above, wherein the weight ratio of dimethyl carbonate to the total weight of solvent in the electrolyte is 0.60 to 0.90.

[0019] [6] The present invention provides a lithium secondary battery according to at least one of [1] to [5] above, wherein the electrolyte comprises at least one additive selected from the group consisting of vinylene carbonate, 1,3-propanesulfonyl lactone, succinate and methylpropynyl carbonate.

[0020] [7] The present invention provides a lithium secondary battery according to at least one of [1] to [6] above, wherein the lithium secondary battery is a cylindrical battery with a shape factor ratio, that is, the ratio of the diameter to the height of the battery casing is 0.4 or more.

[0021] [8] The present invention provides a lithium secondary battery according to at least one of [1] to [7] above, wherein the lithium secondary battery is a 46110 cell, a 48110 cell, a 4880 cell or a 4680 cell.

[0022] [9] The present invention provides a lithium secondary battery according to at least one of [1] to [8] above, wherein the lithium secondary battery includes an uncoated portion on at least a portion of the positive electrode and the negative electrode on which an active material layer is not formed, and the uncoated portion of the positive electrode or the uncoated portion of the negative electrode is defined as an electrode tab.

[0023]

[10] The present invention provides a lithium secondary battery as described in [9] above, wherein the uncoated portion of the positive electrode and the uncoated portion of the negative electrode are respectively formed on one side end of the positive electrode and the negative electrode along the winding direction of the electrode assembly, the current collector is respectively joined to the uncoated portion of the positive electrode and the uncoated portion of the negative electrode, and the current collector is connected to the electrode terminal.

[0024]

[11] The present invention provides a lithium secondary battery as described in [9] or

[10] above, wherein the uncoated portion of the positive electrode and the uncoated portion of the negative electrode are processed into a plurality of independently bendable segments, and at least a portion of the plurality of segments bends toward the winding center of the electrode assembly.

[0025]

[12] The present invention provides a lithium secondary battery as described in

[11] above, wherein at least a portion of the bent plurality of segments overlaps at the upper and lower ends of the electrode assembly, and the current collector is engaged to the overlapping plurality of segments.

[0026]

[13] The present invention provides a battery pack comprising at least one of the lithium secondary batteries described in [1] to

[12] above.

[0027] Beneficial effects

[0028] The lithium secondary battery of the present invention is designed to meet specific conditions regarding specifications and capacity, electrolyte injection amount, DMC ratio in organic solvent, and CH4 volume in the formed cell. This means that a stable film is formed on the electrode through oxidation / reduction reaction during charge and discharge.

[0029] Therefore, the lithium secondary battery of the present invention is a battery that minimizes performance degradation due to the decomposition and regeneration of the electrode film and the decomposition of organic solvents in the electrolyte, and can exhibit excellent life characteristics even if it is a large cylindrical battery with relatively low electrolyte wettability or a battery with a tabless structure. Attached Figure Description

[0030] Figure 1 This is a diagram showing the stacked state of the electrode assembly of the present invention before winding.

[0031] 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.

[0032] Figure 3 This is a diagram illustrating the structure of an electrode assembly according to one embodiment of the present invention.

[0033] Figure 4 This is a cross-sectional view showing the structure of a lithium secondary battery according to one embodiment of the present invention.

[0034] Figure 5 This is a cross-sectional view showing the structure of a lithium secondary battery according to another embodiment of the present invention.

[0035] Figure 6 This is a diagram illustrating the battery pack of the present invention. Detailed Implementation

[0036] The invention will be described in more detail below.

[0037] Generally, in lithium-ion secondary batteries, as solvents and additives in the electrolyte undergo redox reactions on the surfaces of the negative and positive electrodes during formation, a SEI layer (solid electrolyte interphase) and a CEI layer (cathode electrolyte interphase) are formed on the negative and positive electrode surfaces as passivation films. Hydrocarbon gases are mainly generated during the formation of the negative electrode SEI layer, particularly CH4 gas, which is primarily produced when the SEI layer forms on the negative electrode due to the decomposition of electrolyte additives or dimethyl carbonate (DMC), an organic solvent. Specifically, electrolyte additives such as vinylene carbonate (VC) contribute to SEI layer formation. However, if the amount of additives contributing to SEI layer formation is insufficient, dimethyl carbonate (DMC) will be consumed to form the SEI layer. Therefore, a large amount of DMC confirmed after formation indicates that the SEI layer has been sufficiently formed by the additives. Thus, the degree of SEI layer formation can be estimated by examining the volume of CH4 gas and the ratio of DMC present in the battery after formation.

[0038] If too little SEI layer is formed, the increased side reactions between the electrolyte and the electrode surface lead to electrode degradation and gas generation, thus reducing lifetime characteristics. Conversely, if too much SEI layer is formed, the electrode surface resistance increases. Therefore, an appropriate SEI layer must be formed to achieve excellent electrochemical performance in secondary batteries.

[0039] The appropriate degree of SEI layer formation varies depending on a complex combination of factors, including battery specifications and capacity. This is because electrolyte wetting and reaction surface area vary depending on the battery type. Because the degree of SEI layer formation depends on these complex factors, it is difficult to determine the correlation between the degree of SEI layer formation and secondary battery performance.

[0040] However, as a result of continuous research by the inventors, the inventors have discovered a new parameter Y that reflects the battery specifications and the gas composition, electrolyte residue, solvent composition and discharge capacity of the secondary battery after formation. This parameter Y can represent the degree of SEI layer formation. When the Y value meets a specific range, the electrochemical performance of the secondary battery, especially large batteries with low electrolyte wettability or tabless structures, is significantly improved.

[0041] Specifically, the lithium secondary battery of the present invention includes: an electrode assembly comprising a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode; an electrolyte comprising a lithium salt and an organic solvent; and a battery casing accommodating the electrode assembly and the electrolyte, wherein the organic solvent comprises dimethyl carbonate, and the Y value defined by the following mathematical formula 1 can be from 0.15 to 0.30, preferably from 0.15 to 0.25, more preferably from 0.15 to 0.23.

[0042] [Mathematical Expression 1]

[0043] In mathematical formula 1, FF is the ratio of the diameter to the height of the battery casing. E is the amount of electrolyte residue measured in grams. r DMC It is the weight ratio of dimethyl carbonate to the total weight of the solvent in the electrolyte. V CH4 The volume of CH4 gas present in the lithium secondary battery is measured in mL, and C is the discharge capacity of the lithium secondary battery, measured in Ah, when charged and discharged at 0.5 C within the range of 2.5 V to 4.2 V. Where Y is a dimensionless number.

[0044] A Y value less than 0.15 may indicate that the electrolyte injection amount does not meet the standards required by this invention, which is undesirable because it means that the SEI layer may not be sufficiently formed. Conversely, a Y value greater than 0.30 may indicate that an excessive amount of electrolyte has been injected, which is also undesirable because it may lead to excessive additive decomposition reactions, thereby reducing cell performance, for example, by increasing the amount of gas generated in the battery.

[0045] The formation in this invention can be performed, for example, by charging to 4.2V at 0.2C and discharging to 2.5V at 25°C. Specifically, the formation can be performed by charging to 3.8V at 0.2C at 25°C, storing at 60°C for 12 hours, then charging again to 4.2V at 25°C, and then discharging to 2.5V.

[0046] V corresponds to in mathematical formula 1 CH4 The volume of CH4 gas is obtained by measuring the volume of CH4 gas present in the lithium secondary battery after formation, which can be from 4.0 mL to 11.0 mL, preferably from 4.5 mL to 10.0 mL, and more preferably from 4.8 mL to 9.3 mL. Furthermore, the ratio of the volume of CH4 gas to the total volume of gas present in the lithium secondary battery after formation (V...) is also considered. CH4 / V total The ratio of CH4 gas can be from 0.40 to 0.80, preferably from 0.44 to 0.70, and more preferably from 0.60 to 0.67. A CH4 gas ratio within the above range can serve as an indicator of proper SEI layer formation on the negative electrode. The volume of CH4 can be measured by analyzing the trapped gas in the cell using GC-TCD (Gas Chromatography-Thermal Conductivity Detector).

[0047] The electrolyte residue corresponding to the E value in Formula 1 is a value obtained by measuring the amount of electrolyte present in the lithium secondary battery after formation, which can be between 25 g and 32 g. Since some electrolyte is consumed during formation, the electrolyte residue can be approximately 75% to 85% of the injected electrolyte. The electrolyte residue can be measured by NMR (Nuclear Magnetic Resonance) analysis. Specifically, the electrolyte is extracted from the lithium secondary battery, diluted with acetone, and then an internal standard can be added. The absolute content is confirmed by NMR analysis.

[0048] In addition, qualitative analysis of the electrolyte composition can be performed using GC / MS (gas chromatography / mass spectrometry) and relative content analysis using NMR.

[0049] Corresponding to r in mathematical formula 1 DMC The weight ratio of dimethyl carbonate (DMC) represents the ratio of DMC to the total weight of solvent in the electrolyte when the total weight of solvent in the electrolyte present in the lithium secondary battery after formation is set to 1. This ratio can be from 0.60 to 0.90, preferably from 0.65 to 0.85, and more preferably from 0.70 to 0.80. The weight ratio of dimethyl carbonate can be determined by relative content analysis using NMR signal intensity ratios. During the formation process, due to the high temperature, a portion of DMC decomposes into DMDOHC (dimethyl 2,5-dioxaadipic acid), but as described above, DMC is not consumed during the formation of the SEI layer in the lithium secondary battery of the present invention, therefore, a large amount may remain in the form of DMC as described above.

[0050] For the discharge capacity corresponding to the C value in Formula 1, the discharge capacity (C) measured after formation when the lithium secondary battery is charged and discharged at 0.5C in the range of 2.5V to 4.2V, specifically by charging the lithium secondary battery at 0.5C to 4.2V under constant current-constant voltage (CC-CV) conditions at 25°C and then discharging it to 2.5V at a constant power (CP) of 19.1W, can be from 10 Ah to 50 Ah, preferably from 15 Ah to 40 Ah, and more preferably from 20 Ah to 30 Ah.

[0051] In mathematical formula 1, FF is r / h when the height is h and the diameter is r, that is, the ratio of the diameter to the height of the battery casing, which is called the shape factor ratio. FF can be 0.4 or higher, preferably 0.4 to 0.6.

[0052] In other words, a lithium secondary battery can be a cylindrical battery with a shape factor ratio of 0.4 or higher, preferably 0.4 to 0.6.

[0053] 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.

[0054] Lithium secondary batteries with a Y value of 0.15 to 0.30 that satisfy mathematical formula 1 can be prepared by appropriately adjusting the electrolyte composition according to the shape of the battery casing, the shape of the electrode assembly, and the battery capacity.

[0055] Specifically, the method for preparing the lithium secondary battery of the present invention includes the following steps: preparing an electrode assembly including a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, inserting the electrode assembly into the battery casing, and injecting 30 g to 45 g of electrolyte.

[0056] The electrolyte may contain: a lithium salt; an organic solvent including dimethyl carbonate (DMC); and at least one additive selected from the group consisting of vinylene carbonate (VC), 1,3-propanesulfonyl lactone (PS), succinate (SN), and methylpropynyl carbonate.

[0057] Based on the total weight of the organic solvent, the organic solvent may contain 60% to 90% by weight of dimethyl carbonate.

[0058] The components of the lithium secondary battery of the present invention will now be described in more detail.

[0059] 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.

[0060] electrolytes

[0061] The electrolyte of the present invention comprises a lithium salt and an organic solvent.

[0062] Any lithium salt commonly used in electrolytes for lithium secondary batteries can be used without limitation. Specifically, the lithium salt may contain Li. + As a cation, and may contain F-selected - 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 - BF2C2O4CHF - PF4C2O4 - PF2C4O8 - PO2F2 - (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 of the groups constitutes an anion.

[0063] Specifically, the lithium salt can be at least one selected from the group consisting of LiPF6, LiClO4, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethanesulfonate (LiSO3CF3), lithium difluorophosphate (LiPO2F2), lithium dioxalate borate (LiBOB), lithium difluorooxalate borate (LiFOB), lithium difluorodioxalate phosphate (LiDFOP), lithium tetrafluorooxalate phosphate (LiTFOP), and lithium difluoromalonic acid difluoroborate (LiFMDFB), preferably LiPF6.

[0064] In one embodiment of the invention, the concentration of the lithium salt in the non-aqueous organic solution containing the lithium salt and the organic solvent can be from 0.5 M to 4.0 M, specifically from 0.5 M to 3.0 M, and more specifically from 1.2 M to 2.0 M. When the concentration of the lithium salt is within the above range, appropriate electrolyte wettability can be obtained because the effects of improving low-temperature output and improving cycle characteristics can be sufficiently ensured while preventing excessive increases in viscosity and surface tension.

[0065] As an organic solvent, various organic solvents commonly used in lithium electrolytes can be used in conjunction with dimethyl carbonate (DMC). For example, the organic solvent may also include cyclic carbonate solvents, linear carbonate solvents, linear ester solvents, cyclic ester solvents, nitrile solvents, or mixtures thereof, preferably a mixture of cyclic carbonate solvents and linear carbonate solvents including DMC. A mixture of cyclic carbonate solvents and linear carbonate solvents is ideal for improving the ionic conductivity of the electrolyte.

[0066] The linear carbonate solvent is a low-viscosity, low-dielectric-constant organic solvent. In addition to dimethyl carbonate (DMC), at least one selected from the group consisting of diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate may also be used. Electrolyte additives, particularly vinylene carbonate (VC), primarily contribute to the formation of the SEI layer. If the amount of additive contributing to SEI layer formation is insufficient, DMC will be consumed instead to form the SEI layer. Therefore, a large amount of DMC confirmed after formation indicates that the SEI layer has been sufficiently formed by the additives.

[0067] Cyclic carbonate solvents, due to their high dielectric constant as high-viscosity organic solvents, can effectively dissociate lithium salts in electrolytes. The cyclic carbonate solvent can be at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentene carbonate, 2,3-pentene carbonate, and vinylene carbonate, and is preferably ethylene carbonate (EC) or propylene carbonate (PC) or a mixture thereof.

[0068] The linear ester solvent can be at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate, and is preferably methyl propionate, ethyl propionate or propyl propionate.

[0069] The cyclic ester solvent can be at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone.

[0070] The nitrile solvent may be at least one selected from the group consisting of succinic anionyl nitrile, acetonitrile, propionitrile, butyronitrile, valerate, octanoic anionyl nitrile, heptanoic anionyl nitrile, cyclopentaneformitrile, cyclohexaneformitrile, 2-fluorobenzyl nitrile, 4-fluorobenzyl nitrile, difluorobenzyl nitrile, trifluorobenzyl nitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, and may preferably be succinic anionyl nitrile.

[0071] If necessary, the electrolyte may contain at least one additive selected from the group consisting of cyclic carbonates, sulfonyl lactones, sulfates or salts, phosphorus compounds, nitriles, amines, silanes, benzenes, and lithium salts.

[0072] The cyclic carbonate compound may be at least one selected from the group consisting of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC) and methylpropynyl carbonate, specifically vinylene carbonate.

[0073] Sulfolactone compounds are materials capable of forming a stable SEI layer on the negative electrode surface through a reduction reaction. The sulfolactone compounds can be at least one compound selected from the group consisting of 1,3-propanesulfonolactone (PS), 1,4-butanesulfonolactone, ethanesulfonolactone, prop-1-ene-1,3-sulfonolactone (PRS), 1,4-butenesulfonolactone, and 1-methyl-1,3-propenesulfonolactone, specifically 1,3-propanesulfonolactone (PS) or prop-1-ene-1,3-sulfonolactone (PRS).

[0074] Sulfate esters or salt compounds are materials capable of forming a stable SEI layer that will not crack even during high-temperature storage by electrolysis on the negative electrode surface, wherein the sulfate ester or salt compound can be at least one selected from the group consisting of ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyltrimethyl sulfate (MTMS).

[0075] Phosphorus compounds can be phosphate esters or salts or phosphites or salts, specifically, at least one selected from the group consisting of tri(trimethylsilyl) phosphate, tri(trimethylsilyl) phosphite, tri(2,2,2-trifluoroethyl) phosphate, and tri(trifluoroethyl) phosphite.

[0076] The nitrile compound may be at least one selected from the group consisting of succinic anionyl (SN), adiponitrile (ADN), acetonitrile, propionitrile, butyronitrile, valerate, octanoic anionyl, heptanoic anionyl, cyclopentaneformitrile, cyclohexaneformitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, ethylene glycol di(2-cyanoethyl) ether (ASA3), 1,3,6-hexanetricarbonitrile (HTCN), 1,4-dicyano-2-butene (DCB), and 1,2,3-tris(2-cyanoethyl)propane (TCEP).

[0077] The amine compound may be at least one selected from the group consisting of triethanolamine and ethylenediamine, and the silane compound may be tetravinylsilane.

[0078] Benzene compounds can be at least one selected from the group consisting of monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene.

[0079] Lithium salt compounds are compounds that are different from lithium salts contained in non-aqueous electrolytes. The lithium salt compounds may be at least one compound selected from the group consisting of lithium difluorophosphate (LiDFP; LiPO2F2), lithium dioxolane-borate (LiBOB; LiB(C2O4)2), lithium tetrafluoroborate (LiBF4), lithium tetraphenylborate, lithium difluorooxolane-borate (LiDFOB), and lithium difluorodioxolane-phosphate (LiDFOP).

[0080] Preferably, it may contain at least one additive selected from the group consisting of vinylene carbonate (VC), 1,3-propanesulfonyl lactone (PS), succinate (SN) and methylpropynyl carbonate as an additive that helps form the SEI layer.

[0081] Based on the total weight of the electrolyte, the total content of the additives can be from 3% to 7% by weight, preferably from 4% to 6% by weight.

[0082] When the amount of additives that help form the SEI layer is insufficient, the amount of electrolyte injected itself is increased to compensate for this. In this case, the Y value is greater than 0.30, which may lead to a decrease in cell performance, for example, due to an increase in gas production caused by side reactions in the cell.

[0083] Except for the amount of lithium salt and additives, the remainder of the electrolyte may be an organic solvent, unless otherwise stated.

[0084] Electrode assembly

[0085] 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.

[0086] exist Figure 1The figure shows a stacked structure of an electrode assembly before winding, according to one embodiment of the present invention. Figure 2 The diagram shows a cross-sectional structure of an electrode plate (positive or negative electrode) according to one embodiment of the present invention. Figure 3 The diagram illustrates the structure of an electrode assembly according to one embodiment of the present invention.

[0087] See Figure 1 and Figure 2 The electrode assembly A of the present invention can be prepared by winding a stack formed by stacking the diaphragm 12, the positive electrode 10, the diaphragm 12 and the negative electrode 11 in sequence at least once along one direction X.

[0088] In this case, the positive electrode 10 and the negative electrode 11 each have a structure in which an active material layer 21 is formed on the elongated sheet current collector 20, and may include an uncoated portion 22 in which the active material layer 21 is not formed in a certain region of the current collector 20.

[0089] If a positive electrode 10 and a negative electrode 11 including the uncoated portion 22 described above are used, a battery with a tabless structure that does not include separate electrode tabs and where at least a portion of the uncoated portion of the positive electrode 10 and the negative electrode 11 defines the electrode tabs can be realized.

[0090] Specifically, the uncoated portion 22 can be formed longer along the winding direction X at one end of the current collector 20, and can function as an electrode tab by connecting the current collector to the uncoated portion of the positive electrode and the uncoated portion of the negative electrode respectively and connecting the current collector to the electrode terminal.

[0091] For example, a battery in which the uncoated positive and negative electrodes serve as electrode tabs can be fabricated using the following method. First, a separator, a positive electrode, another separator, and a negative electrode are stacked sequentially such that the uncoated positive and negative electrodes are positioned in opposite directions. Then, the electrodes are wound in one direction to create a jelly-roll type electrode assembly. Next, after bending the uncoated positive and negative electrodes towards the winding center C, current collectors are welded to the uncoated positive and negative electrodes, respectively. The battery is then fabricated by connecting the current collectors to the electrode terminals. Since the current collector has a larger cross-sectional area than the strip-shaped electrode tabs, and resistance is inversely proportional to the cross-sectional area of ​​the current-carrying channel, the cell resistance can be significantly reduced when a secondary battery is formed using the above structure.

[0092] The uncoated portions of the positive electrode and the uncoated portions of the negative electrode can be processed into multiple independently bendable segments, and at least a portion of the multiple segments can be bent toward the winding center C of the electrode assembly.

[0093] The fragments can be formed by processing the current collectors of the positive and negative electrodes through metal foil cutting processes such as laser grooving, ultrasonic cutting, and punching.

[0094] When the uncoated portions of the positive and negative electrodes are processed in multiple segments, by reducing the stress applied to the uncoated portions during bending, deformation or damage to the uncoated portions can be prevented, and the welding characteristics with the current collector can be improved.

[0095] The current collector and the uncoated portion are typically joined by welding. To improve welding characteristics, strong pressure must be applied to the weld area of ​​the uncoated portion to bend it as flat as possible. However, during this bending process, the shape of the uncoated portion may irregularly twist and deform, and the deformed portion may come into contact with an electrode of opposite polarity, leading to an internal short circuit or the formation of microcracks in the uncoated portion. However, if the uncoated portions of the positive and negative electrodes are machined into multiple independently bendable segments, the stress applied to the uncoated portion during bending can be reduced, thereby minimizing deformation and damage to the uncoated portion.

[0096] Furthermore, when the uncoated portion is processed in the aforementioned segmented form, the multiple segments overlap during bending, resulting in increased weld strength to the current collector and preventing the problem of laser beams penetrating into the electrode assembly and ablating the diaphragm or active material when using state-of-the-art technologies such as laser welding. Preferably, at least a portion of the bent multiple segments can overlap at the upper and lower ends of the electrode assembly, and the current collector can be joined to the overlapping multiple segments.

[0097] like Figure 3 As shown, the electrode assembly of the present invention can be configured such that an insulating layer 24 is also formed on the positive electrode 10. Specifically, the insulating layer 24 can be configured to cover a portion of the positive electrode active material layer and a portion of the uncoated portion along a direction parallel to the winding direction of the electrode assembly.

[0098] For a battery with a tabless-free structure where the uncoated portion 22c of the positive electrode 10 and the uncoated portion 22a of the negative electrode 11 serve as electrode tabs, the electrode assembly is formed such that the positive electrode 10 protrudes above the separator 12 and the negative electrode 11 protrudes below the separator 12. The protruding positive electrode 10 and / or negative electrode 11 are bent and then joined to the current collector. When the positive electrode 10 or negative electrode 11 is bent as described above, the current collector of the positive electrode 10 or negative electrode 11 crosses the separator and is positioned close to electrodes with opposite polarities. As a result, there is a possibility of positive and negative electrode electrical contact, potentially 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 the uncoated portion, the insulating layer 24 can prevent electrical contact between the positive electrode 10 and the negative electrode 11, thus preventing the battery from short-circuiting.

[0099] Preferably, the insulating layer 24 can be disposed on at least one side of the current collector of the positive electrode 10, and more preferably, it can be disposed on both sides of the positive electrode 10.

[0100] 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, on the surface of the uncoated portion 22c of the positive electrode 10 facing the negative electrode 11 after bending, the insulating layer 24 can be formed by extending to the end of the uncoated portion 22c. However, for the opposite surface to the surface facing the negative electrode 11 after bending, it is preferable that the insulating layer 24 is formed only on a portion of the uncoated portion 22c, for example, before the bending point of the uncoated portion 22c. The reason for this is that if the insulating layer 24 is formed over the entire region of the uncoated portion on the surface opposite to the surface facing the negative electrode 11, it may not be able to function as an electrode tab because it cannot make electrical contact with the current collector.

[0101] The insulating layer 24 can be used as long as it can be attached to the positive electrode while ensuring insulation performance; its material or composition is not particularly limited. 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 are not limited thereto.

[0102] The components of the electrode assembly of the present invention will now be described in more detail.

[0103] positive electrode

[0104] 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. The positive electrode including the 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.

[0105] As the positive current collector, various positive current collectors used in the art can be used. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver can be used as the positive current collector. The thickness of the positive current collector can typically be from 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive active material. The positive current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0106] 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.

[0107] As the aforementioned positive electrode active material, commonly used positive electrode active materials in this field can be used, and there are no particular restrictions on the types.

[0108] Preferably, the positive electrode active material may include a lithium transition metal oxide containing nickel (Ni) and cobalt (Co), and more preferably may include a lithium nickel-based oxide represented by Chemical Formula 1 below.

[0109] [Chemical Formula 1]

[0110] Li a Ni b Co c M 1 d M 2 e O2

[0111] In Chemical Formula 1, M 1 is manganese (Mn), aluminum (Al), or a combination thereof; M 2 is at least one selected from the group consisting of zirconium (Zr), tungsten (W), yttrium (Y), barium (Ba), calcium (Ca), titanium (Ti), magnesium (Mg), tantalum (Ta), and niobium (Nb), a, b, c, d, and e respectively satisfy 0.8 ≤ a ≤ 1.2, 0.50 < b < 1, 0 < c < 0.50, 0 < d < 0.50, 0 ≤ e ≤ 0.1, and b + c + d + e = 1.

[0112] M 1 may preferably be Mn or Mn and Al.

[0113] does not necessarily contain the element M 2 , however, when it is contained in an appropriate amount, it can play a role in promoting grain growth during sintering or improving the crystal structure stability.

[0114] a represents the molar ratio of lithium in the lithium nickel-based oxide, where a can satisfy 0.8 ≤ a ≤ 1.2, 0.85 ≤ a ≤ 1.15, or 0.9 ≤ a ≤ 1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be formed stably.

[0115] b represents the molar ratio of nickel in all metals other than lithium in the lithium nickel-based oxide, where b can satisfy 0.50 < b < 1, 0.60 ≤ b < 1, 0.80 ≤ b < 1, 0.85 ≤ b < 1, or 0.9 ≤ b < 1.

[0116] c represents the molar ratio of cobalt in all metals other than lithium in the lithium nickel-based oxide. Among them, c can satisfy 0 < c < 0.50, 0 < c < 0.40, 0 < c < 0.20, 0 < c < 0.15, or 0 < c < 0.10. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be obtained.

[0117] d represents the molar ratio of element M in all metals other than lithium in the lithium nickel-based oxide 1 , where d can satisfy 0 < d < 0.50, 0 < d < 0.40, 0 < d < 0.20, 0 < d < 0.15, or 0 < d < 0.10. When the molar ratio of element M 1 satisfies the above range, the structural stability of the positive electrode active material is excellent.

[0118] e represents the molar ratio of element M in all metals other than lithium in the lithium nickel-based oxide 2 , where e can satisfy 0 ≤ e ≤ 0.1 or 0 ≤ e ≤ 0.05.

[0119] 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 0.93 Co 0.05 Mn 0.02 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 0.90 Mn 0.03 Co 0.05 Al 0.02 )O2, but not limited thereto.

[0120] The positive electrode paste may optionally further contain at least one of a conductive agent and a binder.

[0121] Conductive agents are used to provide conductivity to the electrodes. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not cause chemical changes in the battery. Specific examples of conductive agents can be: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; carbon-based structures, such as carbon fibers and carbon nanotubes; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives. 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 agent is typically from 1% to 30% by weight, preferably from 1% to 20% by weight, and more preferably from 1% to 10% by weight.

[0122] The adhesive enhances the adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the adhesive include: fluoropolymer adhesives comprising polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber adhesives comprising styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose adhesives comprising carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol adhesives comprising polyvinyl alcohol; polyolefin adhesives comprising polyethylene or polypropylene; polyimide adhesives; polyester adhesives; and silane adhesives, and any one or a mixture of two or more thereof may be used. Based on the total weight of the positive electrode active material layer, the adhesive content may be from 1% to 30% by weight, preferably from 1% to 20% by weight, more preferably from 1% to 10% by weight.

[0123] negative electrode

[0124] 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. 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.

[0125] As the negative current collector, commonly used negative current collectors in the art can be used, such as copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium or silver, and aluminum-cadmium alloys. The thickness of the negative current collector can typically range from 3 μm to 500 μm, and similar to the positive current collector, fine irregularities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. The negative current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams and nonwoven fabrics.

[0126] Alternatively, negative electrode slurry can be prepared by dispersing the negative electrode active material in solvents such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, and water.

[0127] As a negative electrode active material, carbon-based negative electrode active materials used in the art can be used. Alternatively, silicon-based negative electrode active materials can be mixed with carbon-based negative electrode active materials and used as negative electrode active materials.

[0128] As carbon-based active materials, various carbon-based active materials used in this field can be used, such as graphite materials like natural graphite, artificial graphite, and Kish graphite; pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, high-temperature sintered carbon such as petroleum or coal tar pitch-derived coke, soft carbon, and hard carbon. There are no particular limitations on the shape of carbon-based active materials; materials of various shapes such as irregular shapes, planar shapes, flakes, spheres, or fibers can be used.

[0129] In addition, silicon-based anode active materials may include silicon (Si), silicon carbide (SiC), silicon chloride, and silicon oxide (SiO2). k, where 0 < k < 2) and at least one selected from the group consisting of Si - Y1 alloys (where Y1 is an element 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 Y1 can be selected from the group consisting of Mg, Ca, strontium (Sr), Ba, radium (Ra), scandium (Sc), Y, Ti, Zr, hafnium (Hf), (Rf), vanadium (V), Nb, Ta, (Db), chromium (Cr), molybdenum (Mo), W, (Sg), technetium (Tc), rhenium (Re), (Bh), iron (Fe), lead (Pb), ruthenium (Ru), osmium (Os), (Hs), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), boron (B), Al, gallium (Ga), tin (Sn), indium (In), germanium (Ge), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and combinations thereof.

[0130] The weight ratio of the carbon - based anode active material to the silicon - based anode active material contained in the anode slurry can be from 99:1 to 95:10, preferably from 99:1 to 95:5, and more preferably from 97:3 to 95:5.

[0131] When the mixing ratio of the carbon - based anode active material and the silicon - based anode active material satisfies the above range, since the volume expansion of the silicon - based compound is suppressed and the capacity characteristics are improved, excellent cycle performance can be ensured. When the amount of the silicon (Si) - based compound is too small, it is difficult to increase the energy density, so it is difficult to increase the capacity of the battery. When the amount of the silicon (Si) - based compound is too large, the degree of volume expansion of the anode may increase, which is not desirable.

[0132] The anode slurry may optionally further contain at least one of a conductive agent and a binder.

[0133] A conductive agent is used to provide conductivity to the negative electrode. Any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not cause chemical changes in the battery. Specific examples of conductive agents can be: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; carbon-based structures, such as carbon fibers and carbon nanotubes; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives. 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 agent is typically from 1% to 30% by weight, preferably from 1% to 20% by weight, and more preferably from 1% to 10% by weight.

[0134] The adhesive enhances the adhesion between particles of the negative electrode active material and between the negative electrode active material and the negative electrode current collector. Specific examples of the adhesive include: fluoropolymer adhesives comprising polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber adhesives comprising styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose adhesives comprising carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol adhesives comprising polyvinyl alcohol; polyolefin adhesives comprising polyethylene or polypropylene; polyimide adhesives; polyester adhesives; and silane adhesives, and 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 adhesive content can be from 1% to 30% by weight, preferably from 1% to 20% by weight, more preferably from 1% to 10% by weight.

[0135] diaphragm

[0136] 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 typically used in lithium-ion secondary batteries. Specifically, porous polymer membranes can be used, such as those made from polyolefin polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), or laminated structures of two or more layers. Alternatively, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, coated separators incorporating ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength.

[0137] Lithium secondary batteries

[0138] Next, the lithium secondary battery of the present invention will be described.

[0139] Examples of the lithium secondary battery of the present invention are disclosed in Figure 4 and Figure 5 In the following text, reference will be made to... Figure 4 and Figure 5 The lithium secondary battery of the present invention will be described. 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 scope of disclosure.

[0140] exist Figure 4 The figure shows a cross-sectional view of a lithium secondary battery with a tabless structure according to one embodiment of the present invention.

[0141] 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.

[0142] In this case, the electrode assembly can be a stack of a positive electrode, a separator, and a negative electrode wound in one direction. Furthermore, the positive and negative electrodes of the electrode assembly each include an uncoated portion without an active material layer, and they 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 above, only components other than the electrode assembly will be described below.

[0143] The battery casing 142 is a can-shaped container with an opening at the top, wherein it is formed of a conductive metal material such as aluminum or steel. The battery casing houses the electrode assembly 141 in the internal space through the opening at the top, and also houses the electrolyte (not shown).

[0144] Ideally, the lithium secondary battery 140 of the present invention does not include a current interruption device (CID).

[0145] like Figure 4 As shown, the battery casing 142 is electrically connected to the uncoated portion 146b of the negative electrode and can act as a negative terminal that contacts an external power source to transfer current applied from the external power source to the negative electrode.

[0146] If necessary, a rolled edge 147 and a crimped portion 148 may be included at the upper end of the battery housing 142. The rolled edge 147 can be formed by pressing the outer peripheral surface of the battery housing 142 into the distance D1. The rolled edge 147 prevents the electrode assembly 141 housed inside the battery housing 142 from escaping through the upper opening of the battery housing 142, and can also act as a support for stably placing the sealing body 143.

[0147] The crimping portion 148 may be formed on the upper part of 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.

[0148] Next, a sealing body 143 is used to seal the open end of the battery housing 142, comprising a cover plate 143a and a first gasket 143b. The first gasket 143b provides an airtight seal and insulation between the cover plate 143a and the battery housing 142, and may further include a connecting plate 143c electrically and mechanically connected to the cover plate 143a if necessary. The cover plate 143a can be pressed onto a rolled edge 147 formed in the battery housing 142 and can be secured by a crimping portion 148.

[0149] The cover plate 143a is a component formed of a conductive metallic material, which 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 cylindrical secondary battery. The cover plate 143a may include a protrusion 143d projecting upward from the center C, and the protrusion 143d can contact an external power source to allow current to be applied from an external power source.

[0150] 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 to electrically insulate the battery housing 142 and the cover plate 143a.

[0151] 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).

[0152] 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.

[0153] It may also include a first collector plate 144 and / or a second collector plate 145.

[0154] A first current collector 144 is attached to the upper part of the electrode assembly 141. The first current collector 144 is formed of a conductive metal material such as aluminum, copper, and 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 and can be attached to a connecting plate 143c, or it can be directly attached to the lower surface of the cover plate 143a. The lead 149 and other components can be joined 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.

[0155] The first current collector 144 is joined to the end of the uncoated portion 146a of the positive electrode. The joining can be performed by methods such as laser welding, resistance welding, ultrasonic welding, and brazing.

[0156] The second current collector 145 is joined to the lower part of the electrode assembly 141. The second current collector 145 is formed of a conductive metal material such as aluminum, copper, or nickel, and is electrically connected to the uncoated portion 146b of the negative electrode. One surface of the second current collector 145 can be joined to the uncoated portion 146b of the negative electrode, and the opposite surface can be joined to the inner bottom surface of the battery casing 142. In this case, the joining can be performed by methods such as laser welding, resistance welding, ultrasonic welding, and brazing.

[0157] 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 surface 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 peripheral surface of the battery casing 142 can be prevented.

[0158] The insulator 146 includes a lead hole 151, allowing a lead 149 extending upward from the first current collector 144 to be led out. The lead 149 is led 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.

[0159] Insulator 146 may be formed from insulating polymer resin (e.g., polymer resin materials such as polyethylene, polypropylene, polyimide or polybutylene terephthalate).

[0160] If necessary, the lithium secondary battery 140 of the present invention may further include a 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 thinner thickness compared to the surrounding area. Because the venting portion 152 is thinner, it is structurally weaker compared to the surrounding area. Therefore, if the pressure in the lithium secondary battery 140 increases above a certain level, the venting portion 152 ruptures and the gas in the battery casing 152 can be discharged to the outside, thereby preventing the battery from exploding.

[0161] exist Figure 5 The figure shows a cross-sectional view of a lithium secondary battery with a tabless structure according to another embodiment of the present invention.

[0162] See Figure 5 Another embodiment of the lithium secondary battery 170 of the present invention and Figure 4 The lithium secondary battery 140 shown has a different battery casing and sealing structure, but has substantially the same electrode assembly and electrolyte composition.

[0163] 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 to a through hole (the first opening at the first end) of the battery housing 171 with an insulating second washer 173 disposed therebetween. The rivet terminal 172 protrudes to the outside in a direction opposite to the direction of gravity.

[0164] 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 and be electrically connected 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.

[0165] 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, formed 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, this prevents short circuits caused by contact between the uncoated portion B3 of the outer periphery of the electrode assembly 141 and the inner surface of the battery casing 171, which has a different polarity. 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.

[0166] A second washer 173 is disposed between the battery housing 171 and the rivet terminal 172 to prevent electrical contact between the battery housing 171 and the rivet terminal 172, which have opposite polarities. Therefore, the upper surface of the battery housing 171, which has a substantially flat shape, can serve as the positive terminal of the cylindrical battery 170.

[0167] 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 the riveting process and be tightly attached to the inner surface of the battery housing 171. The second washer 173 can be formed, for example, from an insulating polymer resin.

[0168] The washer protrusion 173a of the second washer 173 may have an extended shape to cover the outer peripheral surface of the terminal protrusion 172a of the rivet terminal 172. With the second washer 173 covering the outer peripheral surface 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 peripheral surface of the terminal protrusion 172a but also a portion of its upper surface.

[0169] When the second gasket 173 is formed 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 gasket 173 and the rivet terminal 172, as well as at the interface between the second gasket 173 and the battery housing 171. When the gasket protrusion 173a of the second gasket 173 has a shape extending to the upper surface of the terminal protrusion 172a, the rivet terminal 172 can be integrally joined to the second gasket 173 via injection molding.

[0170] The area 175 on 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 polarity opposite to that of the rivet terminal 172.

[0171] The second current collector 176 is attached to the lower part of the electrode assembly 141. The second current collector 176 is formed of a conductive metal material such as aluminum, steel, copper and nickel, and is electrically connected to the uncoated portion 146b of the negative electrode.

[0172] 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 fixed by being disposed between the inner surface of the battery housing 171 and the first washer 178b. In one example, at least a portion of the edge of the second current collector 176 can be fixed to the rolled edge 180 by welding while being supported on the lower end surface of the rolled edge 180 formed at the lower end of the battery housing 171. In a variant example, at least a portion of the edge of the second current collector 176 can be directly welded to the inner wall surface of the battery housing 171.

[0173] The second manifold 176 may have a plurality of irregularities (not shown) radially formed on the surface facing the uncoated portion 146b. When irregularities are formed, the second manifold 176 may be pressed to press the irregularities into the uncoated portion 146b.

[0174] Preferably, the ends of the second manifold 176 and the uncoated portion 146b can be joined by welding, for example, laser welding.

[0175] 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 that in the embodiment described above.

[0176] Preferably, the cover plate 178a is formed of a conductive metal material. However, since the first gasket 178b is disposed between the cover plate 178a and the battery housing 171, the cover plate 178a is not polarized. The seal 178 is used to seal the lower opening of the battery housing 171 and to release gas when the internal pressure of the battery cell 170 increases above a critical value.

[0177] Preferably, the rivet terminal 172, electrically connected to the uncoated portion 146a of the positive electrode, serves as the positive terminal. Furthermore, the portion 175 of the upper surface of the battery casing 171, excluding the rivet terminal 172, electrically connected to the uncoated portion 146b of the negative electrode via the second current collector 176, serves as the negative terminal. As described above, with both electrode terminals 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 for engaging electrical connection components such as busbars. Therefore, the lithium secondary battery 170 can reduce the resistance at the contact portion of the electrical connection components to a desired level.

[0178] When a lithium secondary battery is formed with a tabless structure as described above, the battery with a tabless structure has a smaller current concentration than a conventional battery with electrode tabs, which can effectively reduce the heat generation in the battery and thus improve the thermal stability of the battery.

[0179] The lithium secondary battery of the present invention, as described above, can be used as a unit cell to prepare a battery pack. Figure 6 The diagram schematically illustrates 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 for electrically connecting the lithium secondary battery 1 and a battery pack housing 2 for housing the component. The lithium secondary battery 1 is the lithium secondary battery of the above embodiment. In the figures, for ease of explanation, components such as busbars, cooling units, and external terminals for electrically connecting the lithium secondary battery 1 are omitted.

[0180] 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.

[0181] The present invention will be described in more detail below with reference to specific embodiments.

[0182] <Example: Preparation of Lithium Secondary Batteries>

[0183] Example 1

[0184] 1) Preparation of electrolytes

[0185] A non-aqueous organic solution was prepared by dissolving LiPF6 in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) to achieve a LiPF6 concentration of 1.25 M. An electrolyte was prepared by mixing 3% by weight of vinylene carbonate (VC), 1% by weight of 1,3-propanesulfonyl lactone (PS), 1% by weight of succinic anionyl (SN), 0.5% by weight of methylpropynyl carbonate, and the balance non-aqueous organic solution.

[0186] ii) Preparation of electrode components

[0187] A positive electrode slurry was prepared by adding positive electrode active material, conductive agent, and binder to N-methylpyrrolidone in a weight ratio of 97.5:1.0:1.5. In this case, the composition is Li[Ni] 0.93 Co 0.05 Mn 0.02 Oxides of O2 are used as positive electrode active materials, carbon nanotubes are used as conductive agents, and PVDF is used as a binder.

[0188] The positive electrode is prepared by coating an aluminum current collector with a positive electrode slurry, drying it, and then rolling it.

[0189] A negative electrode slurry was prepared by adding the negative electrode active material, conductive agent, and binder to distilled water in a weight ratio of 95.0:3.5:1.5. In this case, graphite was used as the negative electrode active material, acetylene black as the conductive agent, and styrene-butadiene rubber (SBR) as the binder.

[0190] The negative electrode is prepared by coating a copper current collector with a negative electrode slurry, drying it, and then rolling it.

[0191] A polyethylene diaphragm is placed between the positive and negative electrodes prepared above, and they are stacked in the order of diaphragm, positive electrode, diaphragm and negative electrode, and then wound to prepare a jelly roll electrode assembly.

[0192] iii) Preparation of lithium secondary batteries

[0193] After inserting the electrode assembly prepared as described above into a cylindrical battery can with a diameter of 46 mm and a height of 80 mm, the electrolyte prepared above is injected to prepare a 4680 battery cell. In this case, the electrolyte is such that the E / V ratio of Formula 1 is... CH4 Quantities that satisfy the values ​​listed in Table 1 below are injected.

[0194] Example 2

[0195] In addition to increasing the electrolyte injection volume to adjust E / V as shown in Table 1 below. CH4 Apart from the value, the 4680 battery cell was prepared in the same manner as in Example 1.

[0196] Example 3

[0197] In addition to increasing the electrolyte injection volume to adjust E / V as shown in Table 1 below. CH4 Apart from the value, the 4680 battery cell was prepared in the same manner as in Example 1.

[0198] Example 4

[0199] In addition to increasing the electrolyte injection volume to adjust E / V as shown in Table 1 below. CH4 Apart from the value, the 4680 battery cell was prepared in the same manner as in Example 1.

[0200] Example 5

[0201] In addition to increasing the electrolyte injection volume to adjust E / V as shown in Table 1 below. CH4 Apart from the value, the 4680 battery cell was prepared in the same manner as in Example 1.

[0202] Comparative Example 1

[0203] In addition to changing the amount of vinylene carbonate (VC) to 2% by weight during electrolyte preparation and reducing the electrolyte injection volume, the E / V ratio was adjusted as shown in Table 1 below. CH4 Apart from the value, the 4680 battery cell was prepared in the same manner as in Example 1.

[0204] Comparative Example 2

[0205] Besides excessively increasing the electrolyte injection volume to adjust E / V as shown in Table 1 below. CH4 Apart from the value, the 4680 battery cell was prepared in the same manner as in Example 1.

[0206] Comparative Example 3

[0207] Except for using a cylindrical battery can with a diameter of 21 mm and a height of 70 mm, the 2170 battery cell was prepared in the same manner as in Example 1.

[0208] Comparative Example 4

[0209] In addition to increasing the electrolyte injection volume to adjust E / V as shown in Table 1 below. CH4 Apart from the value, the 2170 cell was prepared in the same manner as Comparative Example 3.

[0210] <Experimental Example>

[0211] Experimental Example 1. E, r DMC V CH4 Measurement of C

[0212] The cells prepared in the examples and comparative examples were charged to 3.8V at 0.2C at 25°C, stored at 60°C for 12 hours, then recharged to 4.2V at 25°C and discharged to 2.5V for the formation process. Next, the gas trapped in the cells was analyzed using GC-TCD (Gas Chromatography-Thermal Conductivity Detector) to measure the volume (V) of CH4 gas. CH4 ) and the total volume of gas produced (V total ).

[0213] In addition, electrolyte was extracted from each cell after the formation process to confirm the ratio of DMC to the total weight of solvent remaining after formation and the amount of residual electrolyte.

[0214] Specifically, after diluting the extracted electrolyte with acetone, an internal standard was added, and the residual electrolyte was determined by NMR analysis.

[0215] Furthermore, the ratio of residual DMC was calculated using relative content analysis based on NMR signal intensity ratios. Additionally, the formed cells were charged to 4.2V at 0.5C under constant current-constant voltage (CC-CV) conditions at 25°C, and then discharged to 2.5V at a constant power (CP) of 19.1W to measure the discharge capacity C.

[0216] Then, the measured V CH4 、E、r DMC Substituting C into mathematical formula 1, we obtain the value of Y, which is listed in Table 1.

[0217] [Table 1]

[0218] According to Table 1, for Comparative Example 3, which is a 2170 cell, it can be confirmed that even though Comparative Example 3 uses an electrolyte with the same composition as Example 1, the Y value according to Formula 1 deviates significantly from the range of 0.15 to 0.30.

[0219] Experimental Example 2. Cell Performance Inspection

[0220] (1) Initial resistance (DCIR) measurement

[0221] Each cell prepared in the Examples and Comparative Examples was charged to 3.8V at 0.2C at 25°C, stored at 60°C for 12 hours, recharged to 4.2V at 25°C, and discharged to 2.5V for formation. Next, each cell was charged to 4.2V (0.05C cutoff) at 0.5C (rated capacity 1C = 25,000 mAh / g) under CC-CV conditions at 25°C, and fully charged to 100% state of charge (SOC). The voltage drop generated when a fully charged battery was discharged at 12.5A for 10 seconds at 25°C was measured, and the DC resistance was calculated using Ohm's law based on the measured values. When the value measured in Example 1 is set as 100%, the relative values ​​of Examples 2 to 5 and Comparative Examples 1 to 4 are calculated and listed in Table 2 below.

[0222] (2) Measurement of initial discharge energy and energy retention rate

[0223] The cells prepared in the examples and comparative examples were charged to 3.8V at 0.2C at 25°C, stored at 60°C for 12 hours, then recharged to 4.2V at 25°C, and discharged to 2.5V for formation. Next, each cell was charged to 4.1V at 48.5 W CP (constant power) at 20°C and discharged to 3.0V at 48.5 W CP using a charge-discharge apparatus. This charge-discharge cycle was defined as one cycle. After one cycle, the initial discharge energy was measured, and the energy retention rate relative to the initial discharge energy was calculated after repeating the same charge-discharge cycle 200 times. The results are listed in Table 2 below.

[0224] For Comparative Examples 3 and 4, since the battery specifications are different from those of Examples 1 to 5, the same evaluation criteria are not suitable, and therefore no performance evaluation was performed.

[0225] [Table 2]

[0226] Based on the results in Table 2, for the batteries of Examples 1 to 5 and Comparative Examples 1 and 2 with the same 4680 specification, it can be confirmed that they exhibit excellent performance in terms of resistance and energy, provided that the Y value according to Formula 1 is in the range of 0.15 to 0.30.

Claims

1. A lithium secondary battery, comprising: The battery comprises an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes; an electrolyte containing a lithium salt and an organic solvent; and a battery casing housing the electrode assembly and the electrolyte. in, The organic solvent comprises dimethyl carbonate, and The value of Y, as defined by mathematical formula 1, ranges from 0.15 to 0.

30. [Mathematical Expression 1] In mathematical formula 1, FF is the ratio of the diameter to the height of the battery casing. E is the amount of electrolyte residue measured in grams. r DMC It is the weight ratio of dimethyl carbonate to the total weight of the solvent in the electrolyte. V CH4 The volume of CH4 gas present in the lithium secondary battery is measured in mL, and C is the discharge capacity of the lithium secondary battery, measured in Ah, when charged and discharged at 0.5 C within the range of 2.5 V to 4.2 V. Where Y is a dimensionless number.

2. The lithium secondary battery as described in claim 1, wherein, The volume ratio of the CH4 gas to the total volume of gas present in the lithium secondary battery is 0.40 to 0.

80.

3. The lithium secondary battery as described in claim 1, wherein, The residual amount of the electrolyte is 25 g to 32 g.

4. The lithium secondary battery as described in claim 1, wherein, When the lithium secondary battery is charged and discharged at 0.5 C in the range of 2.5 V to 4.2 V, the discharge capacity is 10 Ah to 50 Ah.

5. The lithium secondary battery as described in claim 1, wherein, The weight ratio of dimethyl carbonate to the total weight of the solvent in the electrolyte is 0.60 to 0.

90.

6. The lithium secondary battery as described in claim 1, wherein, The electrolyte contains at least one additive selected from the group consisting of vinylene carbonate, 1,3-propanesulfonyl lactone, succinate and methylpropynyl carbonate.

7. The lithium secondary battery as described in claim 1, wherein, The lithium secondary battery is a cylindrical battery with a shape factor ratio, that is, a ratio of the diameter to the height of the battery casing of 0.4 or more.

8. 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.

9. 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 and negative electrodes where no active material layer is formed, and The uncoated portion of the positive electrode or the uncoated portion of the negative electrode is defined as an electrode tab.

10. The lithium secondary battery as described in claim 9, wherein, The uncoated portions of the positive electrode and the negative electrode are respectively formed on one side end of the positive electrode and the negative electrode along the winding direction of the electrode assembly. The current collector is engaged with the uncoated portions of the positive electrode and the negative electrode, and the current collector is connected to the electrode terminals.

11. The lithium secondary battery as described in claim 9, wherein, The uncoated portions of the positive electrode and the uncoated portions of the negative electrode are processed into multiple independently bendable segments, and At least a portion of the plurality of segments bends toward the winding center of the electrode assembly.

12. The lithium secondary battery as described in claim 11, wherein, At least a portion of the multiple curved segments overlap at the upper and lower ends of the electrode assembly, and the current collector is engaged with the overlapping segments.

13. A battery pack comprising the lithium secondary battery of claim 1 as a unit cell.

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