Lithium secondary battery

Abstract

The present invention relates to a secondary battery having excellent impact resistance. The secondary battery according to the present invention comprises: an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case that accommodates the electrode assembly and the electrolyte, and satisfies the following formula (1). Formula (1): Vp + 0.1×C / De≤ Ve ≤ Vp + 0.15×C / De In Formula (1), Ve is a total electrolyte volume (mL) included in the lithium secondary battery, Vp is a total pore volume (mL) of the electrode assembly, C is a battery capacity (Ah), and De is an electrolyte density (g / mL).

Description

lithium secondary battery

[0001] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0129853, filed September 26, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery with reduced electrolyte leakage when the battery case is damaged.

[0003] Lithium secondary batteries are generally manufactured by applying electrode active material slurry to a positive electrode current collector and a negative electrode current collector to manufacture a positive electrode and a negative electrode, laminating them on both sides of a separator to form an electrode assembly of a predetermined shape, and then storing the electrode assembly in a pouch and injecting electrolyte.

[0004] Secondary batteries are classified into pouch type and can type depending on the material of the case that accommodates the electrode assembly. Among these, pouch type secondary batteries are manufactured by performing press processing on a flexible pouch film laminate to form a cup portion, housing the electrode assembly in the cup portion, injecting an electrolyte, and then sealing the seal portion. Can type secondary batteries are manufactured by housing the electrode assembly in a can made of a metal material, injecting an electrolyte, and then assembling a top cap on the top of the can to seal it.

[0005] Pouch-type secondary batteries offer the advantages of being lightweight, space-efficient, and achieving high energy density through the use of stacked electrode assemblies. However, they are more vulnerable to external shocks than can-type secondary batteries. As the usage environments for secondary batteries have diversified, there is a growing demand for superior safety even in harsh environments, necessitating improved shock resistance.

[0006] The present invention is intended to solve the above-mentioned problems, and relates to a lithium secondary battery in which the total pore volume and electrolyte volume of an electrode assembly satisfy specific conditions so as to minimize electrolyte leakage when the battery case is damaged by external impact, etc.

[0007] According to one embodiment, the present invention provides a lithium secondary battery comprising an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte, and satisfying the following formula (1).

[0008] Equation (1): V p + 0.1×C / D e ≤ V e ≤ V p + 0.15×C / D e

[0009] In the above equation (1), V e is the total electrolyte volume (mL) contained in the lithium secondary battery, and V p is the total pore volume of the electrode assembly (mL), C is the battery capacity (Ah), and D e is the electrolyte density (g / mL).

[0010] The total pore volume (V) of the above electrode assembly p ) may be the sum of the total pore volume of the positive electrode, the total pore volume of the negative electrode, and the total pore volume of the separator.

[0011] The above battery capacity (C) may be the discharge capacity in the operating voltage range of the lithium secondary battery.

[0012] The above battery case may be a pouch-type case.

[0013] Meanwhile, the battery case may be a pouch including a barrier layer, a substrate layer formed on one surface of the barrier layer, and a sealant layer formed on the other surface of the barrier layer, and at least one cup portion curved in one direction, and an electrode assembly and an electrolyte may be accommodated in the cup portion of the pouch.

[0014] Additionally, the electrolyte may include an organic solvent and a lithium salt.

[0015] The organic solvent may include at least one selected from the group consisting of ester solvents, ether solvents, ketone solvents, aromatic hydrocarbon solvents, carbonate solvents, alcohol solvents, nitriles, amides, dioxolanes, and sulfolanes.

[0016] When the total pore volume and electrolyte volume of the electrode assembly, such as in the lithium secondary battery according to the present invention, satisfy specific conditions, leakage of the electrolyte can be minimized when the battery case is damaged, while movement of lithium ions inside the battery can be smoothly achieved, so that a lithium secondary battery can be provided that can achieve both battery performance and reduction of electrolyte leakage.

[0017] Figure 1 is an exploded perspective view of a lithium secondary battery according to one embodiment of the present invention.

[0018] Figure 2 is a drawing for explaining the configuration of the pouch.

[0019] Figure 3 is a graph showing the resistance increase rate of pouch-type lithium secondary batteries manufactured in Examples 1 and 2 and Comparative Examples 1, 3, and 6, respectively.

[0020] Figure 4 is a graph showing the resistance increase rate of pouch-type lithium secondary batteries manufactured in Examples 3 and 4 and Comparative Examples 7 and 8, respectively.

[0021] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best possible manner.

[0022]

[0023] Hereinafter, the present invention will be described in more detail.

[0024] Recently, with the increasing demand for high-capacity batteries, such as those for electric vehicles, the rated capacity of secondary battery cells is increasing, leading to a corresponding increase in the size and weight of electrode assemblies. However, as the electrode assembly grows in size and weight, the problem of the electrode assembly moving during external impacts, damaging or even penetrating the battery case, is becoming more severe. This problem is particularly severe in pouch-type batteries, which have low battery case rigidity. Damage to the battery case can lead to electrolyte leakage, which can interfere with the electrical structures within the battery module and cause a short circuit. A short circuit in the battery module can degrade the performance of the battery module or even cause a fire. Therefore, it is necessary to prevent electrolyte leakage or minimize the amount of leakage once it has occurred.

[0025] In order to reduce the amount of electrolyte that may leak when the battery case is damaged, a method of minimizing the amount of excess electrolyte injected can be considered by limiting the amount of electrolyte injected into the battery cell to an amount that can fill all the pores in the electrode assembly. However, in this case, the resistance of the battery cell increases, so an appropriate level of excess electrolyte injected is required.

[0026]

[0027] The inventors of the present invention have conducted repeated research to find a method for minimizing electrolyte leakage when a battery case is damaged while simultaneously minimizing an increase in resistance of a battery cell. As a result, they have discovered that when the total volume of electrolyte in a battery satisfies specific conditions such as the total pore volume of the electrode assembly, battery capacity, and electrolyte density, the amount of electrolyte that may leak when the battery case is damaged can be reduced as much as possible while also minimizing an increase in resistance of the battery cell, thereby completing the present invention.

[0028]

[0029] A lithium secondary battery according to the present invention comprises an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte, and satisfies the following equation (1).

[0030] Equation (1): V p + 0.1×C / D e ≤ V e ≤ V p + 0.15×C / D e

[0031] In the above equation (1), V e is the total electrolyte volume (mL) contained in the lithium secondary battery, and V p is the total pore volume of the electrode assembly (mL), C is the battery capacity (Ah), and D e is the electrolyte density (g / mL).

[0032]

[0033] After the above lithium secondary battery is manufactured, if it is a lithium secondary battery before activation, the total pore volume (V) of the electrode assembly p ) is the sum of the total pore volume of the positive electrode, the total pore volume of the negative electrode, and the total pore volume of the separator, the battery capacity (C) is the discharge capacity in the operating voltage range of the secondary battery, and the electrolyte volume V in the lithium secondary battery eis the volume of electrolyte injected into the secondary battery.

[0034] In addition, when the lithium secondary battery is a lithium secondary battery in which activation has been performed, the total pore volume of the positive electrode, the total pore volume of the negative electrode, and the total pore volume of the separator after the activation process each mean the pore volume after the activation process, and the electrolyte volume V in the lithium secondary battery e refers to the volume of electrolyte remaining in the secondary battery after the activation process.

[0035]

[0036] The total pore volume of the electrode assembly can be calculated based on the pore volume values ​​of the components constituting each of the positive electrode, the negative electrode, and the separator. In addition, the total pore volume of the electrode assembly after activation can be calculated by measuring the volumes of the positive electrode, the negative electrode, and the separator and then adding them. The method for measuring the pore volume of the positive electrode, the pore volume of the negative electrode, and the pore volume of the separator is not particularly limited, and the size (micro) and mesopore volume can be measured using the BET (Brunauer-Emmett-Teller) measurement method using an adsorbent gas such as nitrogen, which is commonly used, or can be measured using the mercury penetrometer which is commonly used.

[0037] Total electrolyte volume V contained in the above lithium secondary battery e When the above equation (1) is satisfied, the leakage of electrolyte when the battery case is damaged can be significantly reduced while the increase in resistance of the battery cell can be minimized.

[0038]

[0039] Specifically, the total electrolyte volume V e Go [V p +0.1×C / D e ] If it is less than the value, the amount of residual electrolyte impregnated in the pores of the electrode assembly becomes too small, which may result in poor lithium ion mobility, and the total electrolyte volume V e Go [V p +0.15×C / D e ] If the amount is greater than the value, the amount of residual electrolyte remaining after being impregnated in the pores within the electrode assembly may become too large, and the amount of electrolyte leakage may significantly increase when the battery case is damaged.

[0040] On the other hand, if the density of the electrolyte is too high, the total electrolyte volume V e As mentioned above [V p +0.1×C / D e ] If the value is small compared to the value, the above equation (1) may not be satisfied, in which case the electrolyte impregnation may be reduced, which may cause a significant increase in battery resistance, and if the density of the electrolyte is too low, the total electrolyte volume V e As mentioned above [V p +0.15×C / D e ] If the value is greater than the value, the above equation (1) may not be satisfied, and in this case, the amount of electrolyte leakage may significantly increase when the battery case is damaged.

[0041] Meanwhile, the total pore volume V of the electrode assembly p It varies depending on the type of positive electrode, negative electrode and separator, the size of the electrode assembly, the battery capacity, etc., and is not particularly limited. According to one embodiment, the total pore volume V of the electrode assembly p It may be about 1 mL to 1,000 mL, specifically about 10 mL to 500 mL, and more specifically about 50 mL to 250 mL.

[0042] In addition, the battery capacity C refers to the discharge capacity of the battery in the driving voltage range, and is not particularly limited, but may be, for example, 50 Ah to 200 Ah, preferably 50 Ah to 150 Ah, and more preferably 60 Ah to 140 Ah. When the capacity C of the secondary battery satisfies the above range, a high-capacity secondary battery can be implemented.

[0043] Meanwhile, the density of the electrolyte may be 1.0 g / mL to 1.4 g / mL, specifically 1.1 g / mL to 1.3 g / mL. If the electrolyte density is too low, lithium ion mobility may be reduced, and the amount of electrolyte leakage may increase when cracks occur, and if the electrolyte density is too high, impregnation may be reduced, which may deteriorate battery performance.

[0044]

[0045] In one embodiment of the present invention, the total electrolyte volume (mL) included in the lithium secondary battery may be, for example, a value in the range of 4.5 mL to 1,030 mL, specifically 15 mL to 520 mL, and more specifically 55 mL to 270 mL.

[0046]

[0047] Meanwhile, the secondary battery according to the present invention may be a pouch-type secondary battery. In this case, the battery case may be a pouch including, for example, a barrier layer, a substrate layer formed on one surface of the barrier layer, and a sealant layer formed on the other surface of the barrier layer, and at least one cup portion recessed in one direction, and an electrode assembly and an electrolyte may be accommodated in the cup portion of the pouch.

[0048]

[0049] Fig. 1 is an exploded perspective view of a pouch-type lithium secondary battery, which is one embodiment of a secondary battery according to the present invention, and Fig. 2 is a cross-sectional view of a pouch film laminate. Hereinafter, with reference to the drawings, a lithium secondary battery according to one embodiment of the present invention will be described in more detail.

[0050]

[0051] pouch

[0052] The above pouch (100) is a battery case for accommodating an electrode assembly and an electrolyte, and includes a barrier layer (20), a substrate layer (10) formed on one surface of the barrier layer, and a sealant layer (30) formed on the other surface of the barrier layer, and includes at least one cup portion (receiving portion) recessed in one direction.

[0053] Specifically, the pouch (100) has flexibility and can be manufactured by inserting a pouch film laminate in which a substrate layer (10), a barrier layer (20), and a sealant layer (30) are sequentially laminated into a press molding device, and applying pressure with a punch to a portion of the pouch film laminate to stretch it, thereby forming a cup portion having a shape that is indented in one direction.

[0054]

[0055] Substrate layer

[0056] The substrate layer (10) is placed on the outermost layer of the pouch to protect the electrode assembly from external impact and electrically insulate it.

[0057] The above-mentioned substrate layer (10) may be made of a polymer material, and for example, may be made of one or more polymer materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, and Teflon.

[0058] The above substrate layer (10) may have a single-layer structure, or may have a multi-layer structure in which different polymer films (12, 14) are laminated, as illustrated in Fig. 2. When the substrate layer (10) has a multi-layer structure, an adhesive layer (16a) may be interposed between the polymer films.

[0059] Meanwhile, the substrate layer (10) may have a total thickness of 10 μm to 60 μm, specifically 20 μm to 50 μm, and more specifically 30 μm to 40 μm. When the substrate layer has a multilayer structure, the thickness includes the adhesive layer. When the substrate layer (10) satisfies the above range, durability, insulation, and formability are excellent. If the substrate layer thickness is too thin, durability is reduced, and the substrate layer may be damaged during the forming process, and if it is too thick, formability may be reduced, the overall thickness of the pouch may increase, and the battery accommodation space may be reduced, which may lower the energy density.

[0060] According to one embodiment, the substrate layer (10) may be a laminated structure of a polyethylene terephthalate (PET) film and a nylon film. In this case, it is preferable that the nylon film is disposed on the barrier layer (20) side, i.e., on the inside, and the polyethylene terephthalate film is disposed on the surface side of the pouch.

[0061] Polyethylene terephthalate (PET) has excellent durability and electrical insulation properties, and when a PET film is placed on the surface side, it exhibits excellent durability and insulation properties. However, in the case of the PET film, the adhesion to the aluminum alloy thin film constituting the barrier layer (20) is weak, and the stretching behavior is also different. Therefore, when the PET film is placed on the barrier layer side, the substrate layer and the barrier layer may be peeled off during the forming process, and the barrier layer may not be stretched uniformly, which may cause a problem of reduced formability. In contrast, since the stretching behavior of a nylon film is similar to that of an aluminum alloy thin film constituting the barrier layer (20), when a nylon film is placed between the polyethylene terephthalate and the barrier layer, an effect of improving formability can be obtained.

[0062] The above polyethylene terephthalate film may have a thickness of 5 µm to 20 µm, specifically 5 µm to 15 µm, and more specifically 7 µm to 15 µm, and the above nylon film may have a thickness of 10 µm to 40 µm, specifically 10 µm to 30 µm, and more specifically 15 µm to 25 µm. When the thicknesses of the polyethylene terephthalate film and the nylon film satisfy the above ranges, excellent formability and post-formed rigidity are exhibited.

[0063]

[0064] barrier layer

[0065] The barrier layer (20) is intended to secure the mechanical strength of the pouch (100), block the ingress of gas or moisture from outside the secondary battery, and prevent leakage of electrolyte.

[0066] The barrier layer (20) may have a thickness of 30 µm to 100 µm, specifically 35 µm to 80 µm, and more preferably 40 µm to 80 µm. When the barrier layer thickness satisfies the above range, the formability is improved, thereby increasing the cup portion forming depth, or reducing the occurrence of cracks and / or pinholes even during two-cup forming, thereby improving resistance to external stress after forming.

[0067] Meanwhile, the barrier layer (20) may be made of a metal material, and specifically, may be made of an aluminum alloy thin film.

[0068] The above aluminum alloy thin film may include one or more kinds selected from the group consisting of aluminum and metal elements other than aluminum, for example, iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0069] Preferably, the aluminum alloy thin film may have an iron (Fe) content of 1.2 wt% to 1.7 wt%, preferably 1.3 wt% to 1.7 wt%, and more preferably 1.3 wt% to 1.45 wt%. When the iron (Fe) content in the aluminum alloy thin film satisfies the above range, even when the cup portion is formed deeply, the occurrence of cracks or pinholes can be minimized.

[0070]

[0071] sealant layer

[0072] The sealant layer (30) is bonded through heat compression to seal the pouch, and is located on the innermost layer of the pouch film laminate (1).

[0073] The sealant layer (30) must have insulating and corrosion resistance properties because it is the surface that comes into contact with the electrolyte and electrode assembly after the pouch is formed, and must completely seal the inside to block material movement between the inside and the outside, so it must have high sealing properties.

[0074] The above sealant layer (30) may be made of a polymer material, and may be made of at least one selected from the group consisting of, for example, polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, and Teflon, and among these, it may include polypropylene (PP) which has excellent mechanical properties such as tensile strength, rigidity, surface hardness, wear resistance, and heat resistance, and chemical properties such as corrosion resistance.

[0075] More specifically, the sealant layer (30) may include polypropylene, cast polypropylene (CPP), acid modified polypropylene, polypropylene-butylene-ethylene copolymer, or a combination thereof.

[0076] The above sealant layer (30) may have a single-layer structure or may have a multi-layer structure including two or more layers made of different polymer materials.

[0077] The sealant layer may have a total thickness of 60 µm to 100 µm, specifically 60 µm to 90 µm, and more specifically 70 µm to 90 µm. If the thickness of the sealant layer is too thin, the sealing durability and insulation may be reduced, and if it is too thick, the flexibility may be reduced and the total thickness of the pouch film laminate may increase, which may lower the energy density per volume.

[0078]

[0079] The above pouch film laminate (1) can be manufactured through a method for manufacturing a pouch film laminate known in the art. For example, the pouch film laminate can be manufactured through a method of attaching a substrate layer (10) to the upper surface of a barrier layer (20) using an adhesive, and forming a sealant layer (30) on the lower surface of the barrier layer (20) using co-extrusion or an adhesive, but is not limited thereto.

[0080]

[0081] A pouch (100) is manufactured by inserting the above-described pouch film laminate into a molding device and applying pressure to a portion of the pouch film laminate with a punch to form a cup portion. At this time, the pressure may be about 0.3 MPa to 1 MPa, specifically about 0.3 MPa to 0.8 MPa, and more specifically about 0.4 MPa to 0.6 MPa. If the pressure is too low during molding of the cup portion, excessive drawing may occur, resulting in wrinkles, and if it is too high, drawing may not occur properly, resulting in a low molding depth.

[0082] Meanwhile, the movement speed of the punch may be 20 mm / min to 80 mm / min, specifically 30 mm / min to 70 mm / min, and more specifically 40 mm / min to 60 mm / min. If the pressure during forming is too low or the movement speed of the punch is too fast, wrinkles due to buckling may occur, and if the pressure during forming is too high or the movement speed of the punch is too slow, the stress concentrated at the corner of the cup portion during forming may increase, which may increase the occurrence of pinholes or cracks.

[0083]

[0084] The pouch (100) of the present invention manufactured through the above method includes a lower case (101), an upper case (102), and a folding part (130) connecting the lower case and the lower case, and the upper case and / or the lower case includes a cup part (110) having a shape that is indented in one direction.

[0085] Specifically, the pouch (100) according to the present invention may be a single-cup shape in which the cup portion (110) is formed only in the lower case (101), as illustrated in FIG. 1, but is not limited thereto, and may be a double-cup shape in which cup portions are formed in both the upper case and the lower case. In the case of a double-cup shape pouch, since the upper case is folded so that the cup portions of the upper case and the cup portions of the lower case face each other after accommodating the electrode assembly and the electrolyte, it is possible to accommodate an electrode assembly having a thicker thickness than a single-cup shape pouch, and thus has the advantage of being advantageous in implementing high energy density.

[0086] The cup portion (110) has a receiving space for receiving the electrode assembly (200). Meanwhile, the pouch (100) may include a terrace (120) around the cup portion (110). The terrace (120) refers to a non-molded portion of the pouch film laminate, i.e., the remaining area excluding the cup portion (110). The terrace (129) is a portion that is sealed through thermal bonding in the process of receiving the electrode assembly (200) in the cup portion (110), injecting the electrolyte, and then sealing.

[0087] The cup portion (110) may include a bottom surface and a peripheral surface. The peripheral surface may connect the bottom surface and the terrace (120). A plurality of peripheral surfaces, more specifically four, may be provided. The bottom surface may cover one side of the electrode assembly (200), and the peripheral surface may surround the perimeter of the electrode assembly (200).

[0088] Meanwhile, the folding portion (130) connects the lower case (101) and the upper case (102), accommodates the electrode assembly (200) in the cup portion (110), and, after injecting the electrolyte, folds so that the upper case (102) can seal the cup portion (110) of the lower case (101). When the folding portion (130) is included, the lower case (101) and the upper case (102) are connected as one piece, so that when performing the sealing process later, the number of sides to be sealed is reduced, thereby improving the processability.

[0089] The above folding portion (130) is formed to be spaced apart from the cup portion (110), and the distance between the folding portion (130) and the cup portion (110) may be 0.5 mm to 3 mm, preferably 0.5 mm to 2 mm. If the folding portion (130) is formed too close to the cup portion (110), folding may not be performed smoothly, and if the folding portion (130) is formed too far from the cup portion (110), the overall volume of the secondary battery may increase, thereby decreasing the energy density per volume. In the case of a two-cup case, the folding portion may be formed to satisfy the above distance for each cup portion.

[0090]

[0091] electrode assembly

[0092] The electrode assembly (200) may include a plurality of electrodes and a plurality of separators that are alternately stacked. The plurality of electrodes may be alternately stacked with the separator in between and include positive and negative electrodes having opposite polarities.

[0093] Additionally, the electrode assembly (200) may be provided with a plurality of electrode tabs (230) welded to each other. The plurality of electrode tabs (230) may be connected to the plurality of electrodes (210) and may protrude outwardly from the electrode assembly (200) to act as a passage through which electrons may move between the inside and the outside of the electrode assembly (200). The plurality of electrode tabs (230) may be located within the pouch (100).

[0094] The electrode tab (230) connected to the positive electrode and the electrode tab (230) connected to the negative electrode may protrude in different directions with respect to the electrode assembly (200). However, this is not limited to the present invention, and the electrode tab (230) connected to the positive electrode and the electrode tab (230) connected to the negative electrode may also protrude in the same direction while being parallel to each other.

[0095] A lead (240) for supplying electricity to the outside of the secondary battery may be connected to a plurality of electrode tabs (230) by spot welding or the like. One end of the lead (240) may be connected to the plurality of electrode tabs (230) and the other end may protrude to the outside of the pouch (100).

[0096] A portion of the lead (240) may be surrounded by an insulating portion (250). For example, the insulating portion (250) may include an insulating tape. The insulating portion (250) may be positioned between the terrace (120) of the first case (101) and the second case (102), and in this state, the terrace (120) and the second case (102) may be thermally fused to each other. In this case, portions of the terrace (120) and the second case (102) may be thermally fused to the insulating portion (250). Accordingly, the insulating portion (250) may prevent electricity generated from the electrode assembly (200) from flowing to the pouch (100) through the lead (240) and maintain the sealing of the pouch (100).

[0097]

[0098] Meanwhile, in the present invention, the electrode assembly (200) may have a ratio of the total length to the total width of 5 to 10, preferably 5 to 8. When the ratio of the total length to the total width satisfies the above range, a high energy density can be achieved in a limited space.

[0099] For example, the electrode assembly may have a total length of 300 mm to 600 mm and a total width of 50 to 150 mm, specifically, a total length of 500 mm to 600 mm and a total width of 50 to 100 mm.

[0100]

[0101] electrolyte

[0102] The electrolyte is used to move lithium ions generated by the electrochemical reaction of the electrodes during charging and discharging of a secondary battery, and may include an organic solvent and a lithium salt.

[0103] Any organic solvent that can serve as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without any particular restrictions.

[0104] The organic solvent may include at least one selected from the group consisting of ester solvents, ether solvents, ketone solvents, aromatic hydrocarbon solvents, carbonate solvents, alcohol solvents, nitriles, amides, dioxolanes, and sulfolanes. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used.Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0105]

[0106] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 5.0 M, and preferably 0.1 to 3.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0107]

[0108] In addition to the electrolyte components, the electrolyte may further include additives for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. Examples of the additives include haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additives may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the total weight of the electrolyte.

[0109]

[0110] Hereinafter, the present invention will be described in more detail through specific examples.

[0111]

[0112] Example 1

[0113] A pouch was prepared by sequentially laminating nylon / polyethylene terephthalate / Al alloy thin film / polypropylene and forming a cup portion.

[0114] Additionally, a non-aqueous electrolyte was prepared by adding an organic solvent having a composition of ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) = 3:2:5 (volume ratio) and 1.0 M LiPF6. The density of the prepared non-aqueous electrolyte was 1.2 g / mL.

[0115] Cathode active material LiNi 0.9 Co 0.06 Mn 0.03 Al 0.01 O 2,A positive electrode slurry was prepared by mixing carbon nanotubes and PVDF binder in a weight ratio of 97.8:0.6:1.6 in N-methylpyrrolidone. The positive electrode slurry was applied to one surface of an aluminum current collector sheet, dried at 120°C, and then rolled to prepare a positive electrode.

[0116] A negative electrode slurry was prepared by mixing a negative electrode active material (graphite), a conductive agent (super C), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in a weight ratio of 96:2:1.5:0.5 in water. The negative electrode slurry was applied to one surface of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode.

[0117] An electrode assembly with a battery capacity of 66 Ah was manufactured by stacking and laminating the positive and negative electrodes and the porous polyethylene separator.

[0118] An electrode assembly with a total void volume of 116 mL was placed in the cup portion, 121.5 mL of the electrolyte was injected, and then sealed. After being fully charged to 4.2 V, it was fully discharged to 2.5 V at 0.3 C to activate it.

[0119]

[0120] Example 2

[0121] A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that 124.2 mL of electrolyte was injected.

[0122]

[0123] Example 3

[0124] An electrode assembly having a battery capacity of 72 Ah and a total pore volume of 128 mL was manufactured using the method described in Example 1, and a pouch-type lithium secondary battery was manufactured using the same method as in Example 1, except that 134.7 mL of electrolyte was injected.

[0125]

[0126]

[0127] Example 4

[0128] A pouch-type lithium secondary battery was manufactured in the same manner as in Example 3, except that 137.1 mL of electrolyte was injected.

[0129]

[0130] Comparative Example 1

[0131] A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that 115.9 mL of electrolyte was injected.

[0132]

[0133] Comparative Example 2

[0134] A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that 127.0 mL of electrolyte was injected.

[0135]

[0136] Comparative Example 3

[0137] A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that 129.8 mL of electrolyte was injected.

[0138]

[0139] Comparative Example 4

[0140] A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that 132.6 mL of electrolyte was injected.

[0141]

[0142] Comparative Example 5

[0143] A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that 138.2 mL of electrolyte was injected.

[0144]

[0145] Comparative Example 6

[0146] A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that 118.8 mL of electrolyte was injected.

[0147]

[0148] Comparative Example 7

[0149] A pouch-type lithium secondary battery was manufactured in the same manner as in Example 3, except that 128.1 mL of electrolyte was injected.

[0150]

[0151] Comparative Example 8

[0152] A pouch-type lithium secondary battery was manufactured in the same manner as in Example 3, except that 140.1 mL of electrolyte was injected.

[0153]

[0154] Experimental Example 1: Measurement of battery capacity and leakage amount

[0155] The pouch-type lithium secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 8 were charged in CC / CV mode at a constant current (CC) of 0.2 C at 25°C until the voltage reached 4.25 V (end current 0.05 C), then left to stand for 20 minutes and discharged in CC mode until the voltage reached 2.5 V at a constant current (CC) of 0.2 C to measure the discharge capacity. At this time, 1 C = 200 mA / g was set.

[0156] Then, a crack measuring approximately 1 cm × 2 mm was formed on the outer shell of the pouch-type lithium secondary battery manufactured in Examples 1 to 4 and Comparative Examples 1 to 8, respectively.

[0157] Each pouch-type lithium secondary battery was placed in a tray with the crack formed in the pouch facing downward, left for 60 minutes, and then the amount of leaked electrolyte was measured.

[0158] The results are shown in Tables 1 and 2, respectively, along with the satisfaction of Equation 1 below.

[0159] Equation (1): V p + 0.1×C / D e ≤ V e ≤ V p + 0.15×C / D e

[0160] In the above equation (1), V e is the total electrolyte volume (mL) contained in the lithium secondary battery, and V p is the total pore volume of the electrode assembly (mL), C is the battery capacity (Ah), and D e is the electrolyte density (g / mL).

[0161]

[0162] Total pore volume of the electrode assembly (mL) Battery capacity (Ah) Electrolyte density (g / mL) Total injected electrolyte volume (mL) Leakage amount (mL) Equation 1 Satisfaction Example 1 1116661.2121.5 0.01 O Example 2 1116661.2124.20.03 O Comparative Example 1 1116661.2115.9 0.0 X Comparative Example 2 116661.2127.00.4 X Comparative Example 3 1116661.2129.8 1.5 X Comparative Example 4 116661.2132.62.2 X Comparative Example 5 116661.2138.24.2 X Comparative Example 6 116661.2118.8 0.0 X

[0163] Value of Equation (1): 121.5 ≤ Ve ≤ 124.25

[0164] Total pore volume of the electrode assembly (mL) Battery capacity (Ah) Electrolyte density (g / mL) Total injected electrolyte volume (mL) Leakage amount (mL) Equation 1 Satisfaction Example 3 128721.2134.70.09 O Example 4 128721.2137.00.14 O Comparative example 7 128721.2128.10.0 X Comparative example 8 128721.2140.10.68 X

[0165] Value of Equation (1): 134 ≤ Ve ≤ 137

[0166]

[0167] Experimental Example 2: Measurement of Cycle Resistance Increase Rate

[0168] The pouch-type lithium secondary batteries manufactured in Examples 1 and 2 and Comparative Examples 1, 3, and 6, respectively, were charged in CC / CV mode at a constant current (CC) of 0.5 C at 45°C until the voltage reached 4.25 V (end current 0.05 C), then left to stand for 20 minutes and discharged in CC mode at a constant current (CC) of 1.0 C until the voltage reached 2.5 V. The charge / discharge cycles were repeated up to 400 times, and the resistances at the 200th and 400th cycles were measured to calculate the resistance increase rate compared to the initial resistance. The results are shown in Fig. 3.

[0169] In addition, the pouch-type lithium secondary batteries manufactured in Examples 3 and 4 and Comparative Examples 7 and 8 were subjected to 1200 cycles of charge and discharge in the same manner as described above, and the resistances at the 100th, 200th, 400th, 600th, 800th, 1000th, and 1200th cycles were measured to calculate the resistance increase rate compared to the initial resistance. The results are shown in Fig. 4.

[0170]

[0171] Referring to Table 1 above, it can be confirmed that Examples 1 and 2 showed a significantly reduced electrolyte leakage compared to Comparative Examples 2 to 5 when a crack was formed in the pouch. In addition, while Examples 1 and 2 showed a difference of 0.02 mL in the electrolyte leakage amount at a difference of 2.7 mL in the total electrolyte volume, Example 2 and Comparative Example 2 showed a difference of 0.37 mL in the electrolyte leakage amount at a difference of 2.8 mL in the total electrolyte volume (13.3 times), showing a significantly increased electrolyte leakage amount. Through this, it was confirmed that when the volume of additional electrolyte injected during the manufacture of a lithium secondary battery satisfies a certain range, the electrolyte leakage amount can be significantly reduced even when the battery case is damaged. Similarly, as shown in Table 2 above, through a comparison between Examples 3 and 4 and Example 4 and Comparative Example 8, it can be confirmed that Comparative Example 8 showed a significantly increased electrolyte leakage amount compared to the increase in the total electrolyte volume.

[0172] Meanwhile, Comparative Example 1, in which no additional electrolyte was injected, did not experience electrolyte leakage even when the battery case was damaged, but as can be seen in FIG. 3, the resistance increase rate according to the increase in cycles was significantly high, which was clearly different from the relatively low resistance increase rate of Examples 1 and 2 and Comparative Example 3, in which additional electrolyte was injected.

[0173] In addition, in the case of Comparative Examples 6 and 7, in which a small amount of additional electrolyte was injected, no electrolyte leakage occurred even when the battery case was damaged, but as can be confirmed through FIGS. 3 and 4, respectively, it was confirmed that the resistance increase rate according to the increase in cycles was significantly high. In Comparative Examples 6 and 7, even though an electrolyte volume sufficient to fill the total pore volume of the electrode assembly was injected, they showed a high resistance increase rate. Through this, it was confirmed that even when a large volume of electrolyte was injected compared to the total pore volume of the electrode assembly, if the volume of the additionally injected electrolyte was insufficient to satisfy Equation (1), the resistance increase rate according to the increase in cycles could be significantly high.

[0174] Through such experiments, it was confirmed that when an electrolyte volume satisfying Equation (1) is injected, a lithium secondary battery can be manufactured that exhibits excellent cycle characteristics while minimizing electrolyte leakage when the battery case is damaged.

Claims

1. A lithium secondary battery comprising an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte, and satisfying the following formula (1): (1): V p + 0.1×C / D e ≤ V e ≤ V p + 0.15×C / D e In the above equation (1), V e is the total electrolyte volume (mL) contained in the lithium secondary battery, and V p is the total pore volume of the electrode assembly (mL), C is the battery capacity (Ah), and D e is the electrolyte density (g / mL).

2. In paragraph 1, Total pore volume V of the above electrode assembly p A lithium secondary battery having a total pore volume of the positive electrode, a total pore volume of the negative electrode, and a total pore volume of the separator.

3. In paragraph 1, Total pore volume V of the above electrode assembly p A lithium secondary battery having a volume of 1 mL to 1,000 mL.

4. In paragraph 1, A lithium secondary battery, wherein the above battery capacity C is a discharge capacity in the operating voltage range of the secondary battery.

5. In paragraph 1, A lithium secondary battery having a battery capacity C of 50 Ah to 200 Ah.

6. In paragraph 1, The above electrolyte density D e A lithium secondary battery having a density of 1.0 g / mL to 1.4 g / mL.

7. In paragraph 1, The above battery case is a lithium secondary battery in a pouch-type case.

8. In paragraph 1, The battery case is a pouch including a barrier layer, a substrate layer formed on one surface of the barrier layer, and a sealant layer formed on the other surface of the barrier layer, and including at least one cup portion curved in one direction. A lithium secondary battery in which an electrode assembly and an electrolyte are accommodated in the cup portion of the above pouch.

9. In paragraph 1, A lithium secondary battery wherein the electrolyte comprises an organic solvent and a lithium salt.

10. In paragraph 9, A lithium secondary battery, wherein the organic solvent comprises at least one selected from the group consisting of ester solvents, ether solvents, ketone solvents, aromatic hydrocarbon solvents, carbonate solvents, alcohol solvents, nitriles, amides, dioxolanes, and sulfolanes.

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