Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery including an electrode assembly having a structure in which a stacked sheet including positive electrode plates and negative electrode plates stacked with a separator disposed therebetween is wound, an electrolyte, a can in which the electrode assembly and the electrolyte are accommodated, and a cap assembly sealing an opening of the can, wherein the positive electrode plate includes a positive electrode collector, a positive electrode material mixture layer disposed on at least one surface of the positive electrode collector, a positive electrode tab electrically connected to the positive electrode collector, and a positive electrode tab protection member protecting the positive electrode tab, wherein X defined by Equation (1) is 200 or less. Equation (1): X = A × B In Equation (1), A is an expansion ratio of the negative electrode plate, and B is a thickness of the positive electrode tab protection member measured in µm.

Description

lithium secondary battery

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0194809 filed on December 23, 2024, and all contents disclosed in said Korean Patent Application are incorporated herein as part of this specification.

[0002] The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery in which lithium precipitation is suppressed during high-rate charging.

[0003] With the technological advancement of electric vehicles, portable electronic devices, and the like, the demand for lithium-ion batteries as an energy source is rapidly increasing.

[0004] Lithium secondary batteries can be classified into can-type batteries, such as cylindrical or prismatic types, and pouch-type batteries, depending on the material of the battery case. A can-type battery is formed by housing a jelly-roll type electrode assembly—manufactured by sequentially stacking sheet-shaped positive plates, separators, and negative plates and then winding them in one direction—into a battery can, and then sealing the can by covering the top with a cap plate. The positive plate and negative plate are respectively equipped with strip-shaped positive and negative tabs, and these tabs are connected to electrode terminals to be electrically connected to an external power source. For reference, the positive electrode terminal is the cap plate, and the negative electrode terminal is the battery can.

[0005] Although can-type batteries have the disadvantage of lower energy density compared to pouch-type batteries, they offer superior safety and lower manufacturing costs, leading to a recent trend of increasing use as batteries for electric vehicles.

[0006] However, in the case of can-type batteries, there is a problem in that it is difficult to impregnate the electrolyte in the center of the electrode due to structural issues with the jelly-roll type electrode assembly, and localized lithium plating occurs during high-rate charging due to compression at the top of the electrode assembly. When lithium plating occurs, battery performance deteriorates rapidly, significantly shortening the lifespan characteristics, and the high-speed charging capacity of the battery is limited, and in severe cases, it may lead to consequences such as combustion or explosion.

[0007] Therefore, in order to develop batteries with excellent rapid charging performance and lifespan characteristics, a solution is required to resolve the problem of lithium precipitation during high-rate charging of can-type batteries.

[0008] The present invention aims to solve the above-mentioned problems by providing a lithium secondary battery capable of achieving excellent rapid charging performance and lifespan characteristics by suppressing the phenomenon of lithium precipitation at the upper portion of the electrode assembly during high-rate charging and discharging.

[0009] [1] The present invention provides a lithium secondary battery having an electrode assembly having a structure in which a laminated sheet comprising a positive plate and a negative plate laminated with a separator is wound, an electrolyte, a can in which the electrode assembly and the electrolyte are contained, and a cap assembly that seals the opening of the can, wherein the positive plate comprises a positive current collector, a positive composite layer disposed on at least one surface of the positive current collector, a positive tab electrically connected to the positive current collector, and a positive tab protection member that protects the positive tab, wherein X defined by the formula (1) is 200 or less.

[0010] Equation (1): X = A × B

[0011] In the above equation (1), A is the expansion rate of the cathode plate defined by the following equation (2), and B is the thickness of the anode tab protection member measured in μm.

[0012] Equation (2): A={(t-t0) / t} ×100

[0013] In the above equation (2), t is the thickness of the measurement cell measured by cutting the cathode plate and the anode plate into sizes of 31 mm × 43 mm to produce two anode samples and three cathode samples, removing the cathode composite layer placed on one side of the cathode current collector from two of the cathode samples to produce a single-sided cathode sample, then stacking them in the order of separator / single-sided cathode / separator / double-sided anode / separator / double-sided cathode / separator / double-sided anode / separator / single-sided cathode / separator to produce an electrode assembly, placing the produced electrode assembly in a pouch, injecting an electrolyte, and sealing to produce a measurement cell, then pressurizing the measurement cell to 0.156 MPa and charging it to 4.2 V under a 0.05 C cut-off condition, and then measuring the thickness of the measurement cell, and t0 is the thickness of the measurement cell measured before the pressurization and charging.

[0014] [2] The present invention provides a lithium secondary battery in which the expansion rate (A) of the negative plate defined by the formula (2) in [1] is 2% to 10%.

[0015] [3] The present invention provides a lithium secondary battery in which the thickness (B) of the positive tab protection member in [1] or [2] is 10 μm to 60 μm.

[0016] [4] The present invention provides a lithium secondary battery in which, in at least one of [1] to [3], the positive tab is disposed in the center of the positive plate.

[0017] [5] The present invention, in at least one of [1] to [4], wherein the anode loading amount is 20 mg / cm² 2 Provides a lithium secondary battery of the above.

[0018] [6] The present invention provides a lithium secondary battery in which, in at least one of [1] to [5], the positive electrode composite layer comprises a positive electrode active material having a bimodal particle size distribution.

[0019] [7] The present invention provides a lithium secondary battery according to [6], wherein the positive active material comprises large particles with an average particle size of 8 μm to 20 μm and small particles with an average particle size of less than 8 μm, and the large particles and small particles each independently comprise a lithium nickel-based oxide represented by the following [Chemical Formula 1].

[0020] [Chemical Formula 1]

[0021] Li x Ni a Co b M 1 c M 2 d O2

[0022] In the above [Chemical Formula 1], M 1 is one or more selected from Mn and Al, and M 2 ... comprises one or more selected from the group consisting of Zr, Y, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.90≤x≤1.1, 0.50≤a<1.0, 0 <b<0.5, 0<c<0.5, 0≤d≤0.1임.

[0023] [8] The present invention provides a lithium secondary battery in which, in at least one of [1] to [7], the cathode plate comprises a cathode current collector, a cathode composite layer disposed on at least one surface of the cathode current collector, and a cathode tab electrically connected to the cathode current collector, and the cathode composite layer comprises a Si-C composite and a graphite-based cathode active material.

[0024] [9] The present invention provides a lithium secondary battery in which, in [8] the Si-C composite and the graphite-based negative electrode active material are included in a weight ratio of 3:97 to 20:80.

[0025]

[0010] The present invention, in at least one of [1] to [9], wherein the cathode loading amount is 10 mg / cm² 2 Provides a lithium secondary battery of the above.

[0026]

[0011] The present invention provides a lithium secondary battery in which, in at least one of [1] to

[0010] , lithium precipitation is not observed at the upper portion of the electrode assembly when the lithium secondary battery is charged and discharged 100 cycles at 40°C under 1.5C charging and 1.5C discharging conditions.

[0027]

[0012] The present invention provides a lithium secondary battery in which, in at least one of [1] to

[0011] , the lithium secondary battery is a cylindrical battery.

[0028] The lithium secondary battery according to the present invention is designed such that the product of the negative electrode expansion rate and the thickness of the positive electrode tab protection member is 200 or less, thereby effectively suppressing the deposition of lithium at the upper portion of the electrode assembly during high-rate charging and discharging. During high-rate charging and discharging, lithium deposition at the upper portion of the electrode assembly mainly occurs in the area where the positive electrode tab protection member is placed. This is believed to be because electrode compression occurs due to the positive electrode tab protection member as the negative electrode expands during high-rate charging and discharging. Accordingly, the inventors have enabled the suppression of lithium deposition at the upper portion of the electrode assembly by adjusting the thickness of the positive electrode tab protection member according to the degree of negative electrode expansion.

[0029] Figure 1 is a drawing showing the degree of indentation of the electrode assembly in the area where the positive tab protection member is attached during high-rate charging and discharging.

[0030] Figure 2 is a drawing showing the phenomenon of electrode assembly compression in the area where the positive tab protection member is not attached during high-rate charging and discharging.

[0031] Figure 3 is a photograph showing the lithium precipitation state after conventional high-rate charging and discharging.

[0032] FIG. 4 is a schematic diagram of a lithium secondary battery according to one embodiment of the present invention.

[0033] The present invention will be described in more detail below.

[0034] In the present invention, "cathode expansion rate (A)" is used to indicate the degree of volume expansion of the cathode when fully charged, and refers to a value measured by the following method.

[0035] Method for Measuring Cathode Expansion Rate

[0036] After separating the negative and positive plates to be measured for expansion in a lithium secondary battery, the separated negative and positive plates are each punched into sizes of 31 mm × 43 mm to produce two positive samples and three negative samples. Among the two negative samples, a negative composite layer placed on one side of the negative current collector is removed to produce a cross-sectional negative sample.

[0037] Then, an electrode assembly is manufactured by stacking the anode sample and the cathode sample in the order of separator / single-sided cathode / separator / double-sided anode / separator / double-sided cathode / separator / double-sided anode / separator / single-sided cathode / separator.

[0038] The above electrode assembly is placed in a pouch, an electrolyte is injected, and the seal is sealed to manufacture a measuring cell, and the thickness t0 of the measuring cell is measured.

[0039] The above measuring cell is placed on a jig, pressurized to 0.156 MPa, and then charged to 4.2 V under a 0.05 C cut-off condition. Once charging is complete, the measuring cell is removed from the jig, and the thickness t of the charged measuring cell is measured.

[0040] The cathode expansion rate A can be measured by substituting the t-0 and t measured above into the following equation (2).

[0041] Equation (2): A={(t-t0) / t} ×100

[0042] In the present invention, the “loading amount” can be measured by the following method. First, the electrode assembly is disassembled to separate the anode and the cathode, and then the anode and cathode are each stamped out to a size of 5 cm × 5 cm to produce an anode sample and a cathode sample. Then, the weight of each sample is measured using an electron low rate with an effective range of 0.0001 g, and after subtracting the weight of the current collector from the weight of the sample, the area of ​​the sample (25 cm²) 2 The loading amount can be measured by dividing it into ). In the present invention, for accuracy, five samples were prepared by stamping five times per electrode, and the average value of the loading amount measured in each sample was evaluated as the loading amount.

[0043]

[0044] The inventors conducted repeated research to solve the problem of battery performance degradation caused by lithium precipitation at the upper portion of the electrode assembly during high-rate charging and discharging. As a result, they discovered that lithium precipitation at the upper portion of the electrode assembly can be effectively suppressed by adjusting the thickness of the positive electrode tab protection member according to the negative electrode expansion rate, and thus completed the present invention.

[0045]

[0046] Specifically, the lithium secondary battery according to the present invention comprises an electrode assembly in which a positive plate, a separator, and a negative plate are sequentially stacked and wound, an electrolyte, and a battery case in which the electrode assembly and the electrolyte are housed, wherein the positive plate comprises a positive current collector, a positive composite layer disposed on at least one surface of the positive current collector, a positive tab electrically connected to the positive current collector, and a positive tab protection member protecting the positive tab, wherein X defined by the formula (1) is 200 or less.

[0047] Equation (1): X = A × B

[0048] In the above equation (1), A is the expansion rate of the cathode plate defined by the following equation (2), and B is the thickness of the anode tab protection member measured in μm.

[0049] Equation (2): A={(t-t0) / t} ×100

[0050] In the above equation (2), t is the thickness of the measurement cell measured by cutting the cathode plate and the anode plate into sizes of 31 mm × 43 mm to produce two anode samples and three cathode samples, removing the cathode composite layer placed on one side of the cathode current collector from two of the cathode samples to produce a single-sided cathode sample, then stacking them in the order of separator / single-sided cathode / separator / double-sided anode / separator / double-sided cathode / separator / double-sided anode / separator / single-sided cathode / separator to produce an electrode assembly, placing the produced electrode assembly in a pouch, injecting an electrolyte, and sealing to produce a measurement cell, then pressurizing the measurement cell to 0.156 MPa and charging it to 4.2 V under a 0.05 C cut-off condition, and then measuring the thickness of the measurement cell, and t0 is the thickness of the measurement cell measured before the pressurization and charging.

[0051]

[0052] During high-rate charging, such as rapid charging, the volume of the negative electrode expands rapidly, causing a compression phenomenon in which the electrode assembly is compressed and deformed. Meanwhile, in the case of a wound-type electrode assembly, a protective member may be attached to the positive tab to prevent mechanical damage and short circuits. When the positive tab protective member is attached, the thickness of that part increases, and consequently, a compression phenomenon occurs in the area overlapping with the area where the positive tab protective member is attached, thereby intensifying the deformation of the electrode assembly. Figure 1 illustrates a diagram showing the deformation of the electrode assembly in the area where the positive tab protective member of the wound-type electrode assembly is attached during high-rate charging, and Figure 2 illustrates a diagram showing the deformation of the electrode assembly in the area where the positive tab protective member is not attached. Through Figures 1 and 2, it can be confirmed that the compression phenomenon of the electrode assembly is further intensified in the area where the positive tab protective member is attached. As the compression of the electrode assembly increases, more electrolyte leaks out from that area due to the expansion of the negative electrode during charging. This results in a difference in electrolyte concentration between the area with less compression and the surrounding area, leading to increased resistance and increased lithium deposition. Figure 3 shows a photograph illustrating the occurrence of lithium deposition after high-rate charging of a lithium secondary battery containing a wound-type electrode assembly. Through Figure 3, it can be confirmed that lithium deposition occurred intensively in the area overlapping with the area where the positive tab protection member is attached.

[0053] The present invention designs a lithium secondary battery such that X of the above equation (1), which is expressed as the product of the negative plate expansion rate and the thickness of the positive tab protection member, is 200 or less, thereby reducing the compression of the electrode assembly in the area overlapping with the area where the positive tab protection member is attached during high-rate charging, and thereby suppressing lithium deposition on the upper part of the electrode assembly.

[0054] According to the inventors' research, if X exceeds 200, the compression of the electrode assembly intensifies, leading to increased lithium deposition. As X decreases, the compression of the electrode assembly decreases, but if the thickness of the positive tab protection member is too thin, the short-circuit prevention effect may decrease. Therefore, X may preferably be 50 to 200, more preferably 100 to 200, and even more preferably 100 to 190.

[0055] The expansion rate of the above-mentioned cathode plate is a value measured by manufacturing a stacked electrode assembly using positive and negative samples produced by punching out the cathode and positive plates constituting the electrode assembly to a specific size, housing the stacked electrode assembly in a pouch case, and then charging and discharging under pressurized conditions. The specific method for measuring the expansion rate of the cathode plate is the same as described above. In the case of cylindrical batteries, the degree of expansion of the cathode plate cannot be measured due to the can serving as the outer casing. Therefore, the inventors manufactured a pouch-type battery sample and measured the expansion rate of the cathode plate. Furthermore, in the case of cylindrical batteries, the electrode receives a force in the opposite direction due to the can serving as the outer casing during expansion; to simulate this, the expansion rate was measured under pressurized conditions.

[0056] In the present invention, the expansion rate (A) of the negative electrode plate defined by the above formula (2) may be 2% to 10%, preferably 3% to 10%, and more preferably 3% to 8%. When the expansion rate of the negative electrode plate satisfies the above range, lithium deposition at the upper portion of the electrode assembly can be effectively suppressed. If the expansion rate of the negative electrode plate is too high, deformation of the electrode assembly during high-rate charging is intensified, and as a result, lithium deposition increases.

[0057] The expansion rate of the cathode plate is influenced by the composition of the cathode composite layer, particularly the type and content of the cathode active material, the cathode porosity, the cathode loading amount, and the like. For example, the expansion rate of the cathode plate increases if the content of silicon-based cathode active material, which exhibits significant volume expansion during charging and discharging, increases, or if the cathode porosity capable of absorbing volume changes decreases. Additionally, the expansion rate of the cathode plate increases if the cathode loading amount increases. Therefore, the expansion rate of the cathode plate can be controlled by appropriately adjusting these factors.

[0058] In the present invention, the thickness of the anode tab protection member may be 10㎛ to 60㎛, preferably 20㎛ to 60㎛, and more preferably 30㎛ to 50㎛. When the thickness of the anode tab protection member satisfies the above range, an anode tab protection and lithium precipitation suppression effect can be obtained. If the thickness of the anode tab protection member is too thin, the anode tab protection and short-circuit prevention effects are negligible, and if it is too thick, deformation of the electrode assembly may be exacerbated during high-rate charging and discharging.

[0059]

[0060] FIG. 4 discloses a lithium secondary battery according to the present invention. The lithium secondary battery of the present invention will be described in more detail below with reference to FIG. 4.

[0061] A lithium secondary battery according to the present invention comprises an electrode assembly (110), an electrolyte (not shown), a can (120) in which the electrode assembly and the electrolyte are contained, and a cap assembly (130) for sealing the opening of the can.

[0062]

[0063] Electrode Assembly

[0064] The above electrode assembly (110) has a structure in which a laminated sheet having an anode plate and a cathode plate laminated with a separator is wound, and, for example, may be a jelly-roll type electrode assembly.

[0065] The above positive plate has a positive tab (111a) coupled to a cap assembly (130), and the above negative plate has a negative tab (112a) coupled to a can (120).

[0066] The electrode assembly (110) according to the present invention can be manufactured by winding a laminated sheet formed by sequentially stacking a separator, an anode plate, a separator, and a cathode plate in one direction.

[0067] The above positive and negative plates have a structure in which an electrode composite layer is disposed on at least a portion of a sheet-shaped electrode current collector, and may include a non-absorbent portion in which the electrode current collector is exposed without the electrode composite layer disposed on a portion of the electrode current collector. An positive tab or a negative tab may be electrically connected to the non-absorbent portion. The location of the non-absorbent portion may be the central portion and / or the terminal portion of the electrode current collector. For example, the positive plate may have a middle tap structure in which a non-absorbent portion is formed in the central portion of the positive current collector and a positive tab is connected to the non-absorbent portion. When the positive plate has a middle-tap structure, there is an advantage in that the travel distance of electrons flowing through the tab is shortened, thereby lowering the resistance.

[0068] The above-described cathode plate may have a structure in which a non-existent portion is formed at at least one end of the cathode current collector, and a cathode tab is connected to the non-existent portion. When the cathode tab is formed at one end of the cathode current collector, there is an advantage in that the increase in the outer diameter of the jelly-roll or the occurrence of cathode cracks caused by the step difference of the cathode tab can be suppressed.

[0069]

[0070] positive plate

[0071] The anode plate according to the present invention comprises, for example, an anode composite layer disposed on one or both sides of a sheet-shaped anode current collector, an anode tab electrically connected to the anode current collector, and an anode tab protection member disposed to cover at least a portion of the anode tab.

[0072] The above-mentioned positive current collector may be any positive current collector commonly used in the relevant technical field, for example, aluminum, stainless steel, nickel, titanium, calcined carbon, aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0073] The above positive current collector can typically have a thickness of 3 μm to 500 μm. If necessary, fine irregularities may be formed on the surface of the positive current collector to strengthen the bonding force of the positive active material.

[0074] The above-mentioned anode composite layer includes an anode active material and may further include an anode conductive material and an anode binder as needed.

[0075] The above-mentioned cathode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Nip Co q Mn r )O2(where, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 Examples include )O2(wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are each atomic fractions of independent elements, such that 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc., and any one or more of these compounds may be included.

[0076] Preferably, the positive electrode active material may include a lithium transition metal oxide represented by the following [Chemical Formula 1].

[0077] [Chemical Formula 1]

[0078] Li x Ni a Co b M 1 c M 2 d O2

[0079] In the above chemical formula 1, the M 1 It is one or more selected from Mn and Al, and preferably, for durability, it may be Mn or a combination of Mn and Al.

[0080] M 2 It may include one or more selected from the group consisting of Zr, Y, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S.

[0081] The above x represents the atomic fraction of lithium in the lithium transition metal oxide, and may be 0.90≤x≤1.1, preferably 0.95≤x≤1.08, and more preferably 1.0≤x≤1.08.

[0082] The above a represents the atomic fraction of nickel among metal elements excluding lithium in the lithium transition metal oxide, and may be 0.50≤a<1.0, 0.60≤a≤0.98, 0.65≤a≤0.98, 0.80≤a≤0.98, or 0.83≤a≤0.98. When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0083] The above b represents the atomic fraction of cobalt among the metal elements excluding lithium in the lithium transition metal oxide, where 0 <b<0.5, 0<b<0.4, 0.01≤b≤0.3 또는 0.01≤b≤0.17일 수 있다.

[0084] The above c is M among the metal elements excluding lithium in the lithium transition metal oxide. 1 Representing the atomic fraction of, 0 <c<0.5, 0<c<0.4, 0.01≤c≤0.3 또는 0.01≤c≤0.17일 수 있다.

[0085] The above d is M among the metal elements excluding lithium in the lithium transition metal oxide. 2 It represents the atomic fraction of , which can be 0≤d≤0.1 or 0≤d≤0.05.

[0086] The above-mentioned positive active material may have a bimodal particle size distribution. For example, the above-mentioned positive active material may include large particles with a relatively large average particle size and small particles with a relatively small average particle size. The average particle size of the above-mentioned positive active material may be a value (D50) measured as the particle size when the volume accumulation is 50% in the volume accumulation distribution of the positive active material measured using the laser diffraction method, or the arithmetic mean of the values ​​calculated after measuring the particle sizes of particles observed in differential scanning electron microscope (SEM) analysis in the electrode state.

[0087] For example, the above large particles may have an average particle size of 8㎛ to 20㎛, preferably 10㎛ to 20㎛, more preferably 10㎛ to 18㎛, and the above small particles may have an average particle size of less than 8㎛, preferably 2㎛ to 7㎛, more preferably 3㎛ to 7㎛. When a positive electrode active material having a bimodal particle size distribution as described above is included, the electrode density increases, thereby enabling the realization of high energy density.

[0088] The above large particles and small particles may have the same or different compositions. Specifically, the above large particles and small particles may each independently include a lithium transition metal oxide represented by [Chemical Formula 1].

[0089] The above positive active material may be included in an amount of 60 to 99 weight%, preferably 70 to 99 weight%, and more preferably 80 to 98 weight% based on the total weight of the positive composite layer.

[0090] The above-mentioned anode binder is a component that assists in the bonding of the anode active material and the anode conductive material, as well as the bonding to the current collector. Examples of such anode binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers.

[0091] Typically, the anode binder may be included in an amount of 1 to 20 weight%, preferably 1 to 15 weight%, and more preferably 1 to 10 weight% based on the total weight of the anode composite layer.

[0092] The above-mentioned positive electrode conductive material is a component intended to further enhance the conductivity of the positive electrode active material, and is not particularly limited as long as it is conductive without causing chemical changes in the battery. For example, carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; fluorocarbon powder; conductive powders such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0093] Typically, the anode conductive material may be included in an amount of 1 to 20 weight%, preferably 1 to 15 weight%, and more preferably 1 to 10 weight% based on the total weight of the anode composite layer.

[0094] The above-mentioned anode composite layer can be manufactured by, for example, mixing an anode active material, an anode binder, an anode conductive material, and a solvent to prepare an anode slurry, then coating the anode slurry on one or both sides of an anode current collector, and then drying and rolling.

[0095] The solvent for the anode slurry may include organic solvents such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), and acetone, and may be used in an amount that results in a desirable viscosity when including the anode active material, anode binder, and anode conductive material. For example, the concentration of the solid component, which includes the anode active material and optionally the anode binder and anode conductive material, may be 50 to 95 weight%, preferably 70 to 95 weight%, and more preferably 70 to 90 weight%.

[0096] The above positive composite layer is formed in a portion of the surface of the positive current collector, and a positive tab (111a) is coupled to the area (unprotected portion) where the positive current collector is exposed and the positive composite layer is not formed. The positive tab (111a) is electrically coupled to the positive current collector and the cap assembly (130) to apply current to the positive electrode.

[0097] The anode tab (111a) can be positioned in the center of the anode plate. In this case, the center of the anode plate refers to the area from a point corresponding to 30% of the total length of the anode plate to a point corresponding to 50% of the total length of the anode plate when the electrode assembly is unwound. When the anode tab is positioned in the center of the anode plate, the distance traveled by electrons flowing through the tab is shortened, which has the advantage of reducing resistance.

[0098] At least a portion of the anode tab (111a) is covered by an anode tab protection member. The anode tab protection member is intended to prevent mechanical damage and short circuits of the anode tab (111a), and any anode tab protection member commonly used in the art can be used without limitation. For example, the anode tab protection member may be a protective tape comprising a substrate layer made of an insulating material and an adhesive layer disposed on one side of the substrate layer. The substrate layer may be a resin material such as polypropylene, polyimide, polyethylene terephthalate, etc.

[0099] The above positive tab protection member may have a thickness of 10㎛ to 60㎛, preferably 20㎛ to 60㎛, and more preferably 30㎛ to 50㎛. When the thickness of the positive tab protection member satisfies the above range, the positive tab protection and lithium deposition suppression effects can be obtained. If the thickness of the positive tab protection member is too thin, the positive tab protection and short-circuit prevention effects are negligible, and if it is too thick, deformation of the electrode assembly may be exacerbated during high-rate charging and discharging.

[0100] In the present invention, the anode plate has an anode loading amount of 20 mg / cm² 2 Above, preferably 20 mg / cm² 2 to 40 mg / cm² 2 , more preferably 20 mg / cm² 2 to 30 mg / cm² 2 It is possible. When the anode loading amount satisfies the above range, high energy density can be achieved.

[0101]

[0102] cathode plate

[0103] A cathode plate according to the present invention comprises, for example, a cathode composite layer disposed on one or both sides of a sheet-shaped cathode current collector, and a cathode tab electrically connected to the cathode current collector.

[0104] As the above-mentioned negative current collector, negative current collectors generally used in the relevant technical field may be used, for example, copper, stainless steel, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm. If necessary, fine irregularities may be formed on the surface of the above-mentioned negative current collector to strengthen the bonding strength of the negative active material.

[0105] The above cathode composite layer includes a cathode active material and, if necessary, may further include a cathode conductive material and a cathode binder.

[0106] The above-mentioned negative electrode active material may be any negative electrode active material commonly used in the relevant technical field, for example, carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; SiO β Examples include metal oxides capable of doping and dedoping lithium, such as (0<β< 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used.

[0107] Preferably, the cathode active material may include a Si-C composite and a graphite-based cathode active material.

[0108] The above Si-C composite is a material having a structure in which silicon and carbon are composited by depositing or embedding Si within a carbon matrix. Compared to silicon oxide (SiO), which was conventionally used as a Si-based negative electrode active material, it has lower irreversible capacity and superior conductivity. Therefore, when using a Si-C composite, higher energy density can be achieved compared to when using silicon oxide, and rapid charging performance can be improved.

[0109] Preferably, the Si-C composite may have a Si grain size of 20 nm or less, preferably 1 nm to 20 nm, and more preferably 1 nm to 18 nm. When the grain size of the Si-C composite satisfies the above range, excellent improvement effects on cell resistance characteristics and lifespan characteristics are observed.

[0110] In addition, the above Si-C composite is D 50 This can be 1 µm to 15 µm, preferably 2 µm to 10 µm, more preferably 3 µm to 10 µm. In addition, the Si-C composite is D 10 This can be 5㎛ or less, preferably 1 to 5㎛, and D 90 This can be 6㎛ to 20㎛, preferably 6㎛ to 15㎛. When the particle size distribution of the Si-C composite satisfies the above range, the cathode electrode density is increased, and high energy density can be achieved.

[0111] Meanwhile, while using a Si-C composite as the negative electrode active material can improve capacity and rapid charging performance, there is a problem where lifespan characteristics deteriorate due to volume changes in the Si-C composite during charging and discharging. Therefore, in this invention, by using a Si-C composite together with a graphite-based negative electrode active material, the volume change of the Si-C composite during charging and discharging is suppressed by the graphite-based negative electrode active material, thereby improving lifespan characteristics.

[0112] The graphite-based negative electrode active material comprises artificial graphite. Preferably, the graphite-based negative electrode active material may be a mixture of artificial graphite and natural graphite.

[0113] The above artificial graphite may be included in an amount of 40% to 60% by weight, preferably 45% to 55% by weight, and more preferably 47% to 53% by weight, based on the total weight of the graphite-based negative electrode active material. When the content of artificial graphite in the graphite-based negative electrode active material satisfies the above range, the rate characteristics and processability of the negative electrode are excellent, and the volume expansion of the Si-C composite during charging and discharging is suppressed, thereby improving the lifespan characteristics.

[0114] When the graphite-based cathode active material is a mixture of artificial graphite and natural graphite, the weight ratio of artificial graphite to natural graphite may be 40:60 to 60:40, preferably 45:55 to 55:45, and more preferably 47:53 to 53:47. When the mixing ratio of artificial graphite and natural graphite satisfies the above range, the rate characteristics and processability of the cathode are excellent, and the volume change of the Si-C composite during charging and discharging can be effectively suppressed.

[0115] Meanwhile, in the present invention, the Si-C composite and the graphite-based negative electrode active material may be included in a weight ratio of 3:97 to 20:80, preferably 3:97 to 15:85, and more preferably 5:95 to 10:90. When the mixing ratio of the Si-C composite and the graphite-based negative electrode active material satisfies the above range, both rapid charging performance and lifespan characteristics are excellent.

[0116] The total content of the total negative electrode active material, which is the sum of the graphite-based negative electrode active material and the Si-C composite, may be 80 to 99 weight%, preferably 85 to 99 weight%, and more preferably 90 to 99 weight% with respect to the total weight of the negative electrode composite layer.

[0117] Meanwhile, the above-mentioned cathode conductive material is used to impart conductivity to the cathode, and can be used without special restrictions as long as it is used as a conductive material for a lithium secondary battery. Specific examples of the above-mentioned cathode conductive material include carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. Preferably, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube, or a combination thereof may be used as the above-mentioned cathode conductive material, and it is more preferable to use point-type conductive materials and linear-type conductive materials together in terms of improving conductivity. At this time, the point-shaped conductive material is a material having a particle shape in which the contact form with the negative electrode active material is in the form of a point, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc., and the linear conductive material is a material in which the contact form with the negative electrode active material is in the form of a line, such as carbon fiber, carbon nanotube, etc.

[0118] The above cathode conductive material may typically be included in an amount of 1 to 30 weight%, preferably 1 to 20 weight%, and more preferably 1 to 10 weight% based on the total weight of the cathode composite layer.

[0119] Next, the above-mentioned negative electrode binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector, and any material used as a negative electrode binder for a lithium secondary battery can be used without special restrictions. Specific examples of negative electrode binders include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0120] The above cathode binder may be included in an amount of 1 to 30 weight%, preferably 1 to 20 weight%, more preferably 1 to 10 weight% based on the total weight of the cathode composite layer.

[0121] Meanwhile, the above-mentioned cathode composite layer may be formed as a single-layer structure or a multi-layer structure. When the cathode composite layer is a multi-layer structure composed of two or more layers, the types and / or contents of the cathode active material, cathode binder, and / or cathode conductive material in each layer may differ from one another. By forming the cathode active material layer as a multi-layer structure and varying the composition of each layer, the performance characteristics of the battery, such as rapid charging performance and output characteristics, can be appropriately controlled.

[0122] The above cathode composite layer can be manufactured, for example, by dissolving or dispersing a cathode active material, a cathode binder, a cathode conductive material, and / or a dispersant in a solvent to prepare a cathode slurry composition, then applying the cathode slurry onto a cathode current collector, and then drying and rolling.

[0123] As the solvent for the above-mentioned cathode slurry, common solvents used in the art for manufacturing cathode slurries, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, water, or mixtures thereof may be used. The amount of the solvent used is sufficient if it is sufficient to dissolve or disperse the cathode active material, conductive material, binder, and dispersant, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when coated for cathode manufacturing thereafter.

[0124] The above cathode composite layer is formed in a portion of the surface of the cathode current collector, and a cathode tab (112a) is coupled to the area (unclosed portion) where the cathode current collector is exposed and the cathode composite layer is not formed. The cathode tab (112a) is electrically coupled to the bottom portion of the cathode current collector and the can (120) to apply current to the cathode.

[0125] The above-mentioned cathode tab (112a) may be placed at one end or both ends of the cathode plate. When the cathode tab is placed at the end of the cathode plate, an increase in the outer diameter of the jelly-roll or the occurrence of a cathode crack due to the cathode tab step difference can be suppressed.

[0126]

[0127] The above cathode plate has a cathode loading amount of 10 mg / cm² 2 Ideally, 10 mg / cm² 2 ~ 30 mg / cm² 2 , more preferably 10 to 20 mg / cm² 2 It is possible. When the cathode loading amount satisfies the above range, high energy density can be achieved.

[0128]

[0129] Separator

[0130] The above separator separates the negative and positive plates and provides a pathway for the movement of lithium ions; any separator typically used in lithium secondary batteries can be used without any special restrictions. Specifically, the separator may be a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength.

[0131]

[0132] Electrolytes

[0133] The lithium secondary battery according to the present invention includes an electrolyte.

[0134] The above electrolyte may include an organic solvent and a lithium salt.

[0135] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, 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 low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0136] The above lithium salt can be used without special limitations as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, or combinations thereof. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0 M, more preferably 0.1 to 3.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0137] Meanwhile, in addition to the above components, the electrolyte may additionally include additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. For example, the electrolyte may include at least one additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulfone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0138] Examples of the above-mentioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate.

[0139] Examples of the above-mentioned halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0140] Examples of the above sulfone-based compounds include at least one compound selected from the group consisting of 1,3-propane sulfone (PS), 1,4-butane sulfone, ethen sulfone, 1,3-propene sulfone (PRS), 1,4-butene sulfone, and 1-methyl-1,3-propene sulfone.

[0141] Examples of the above sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0142] Examples of the above-mentioned phosphate compounds include one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyl trimethylsilyl phosphate, trimethylsilyl phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0143] Examples of the above borate compounds include tetraphenylborate, lithium oxalyl difluoroborate (LiODFB), and lithium bisoxalate toborate (LiB(C2O4)2, LiBOB).

[0144] Examples of the above nitrile compounds include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0145] Examples of the above benzene-based compounds include fluorobenzene, examples of the above amine-based compounds include triethanolamine or ethylenediamine, and examples of the above silane-based compounds include tetravinylsilane.

[0146] The above lithium salt-based compound is a compound different from the lithium salt included in the above-mentioned non-aqueous electrolyte, and examples include lithium difluorophosphate (LiDFP), LiPO2F2, or LiBF4.

[0147] The above additive may be included in an amount of 0.1 to 10 weight%, preferably 0.1 to 5 weight%, based on the total weight of the electrolyte.

[0148]

[0149] Can

[0150] The can (120) includes a receiving portion for accommodating the electrode assembly (110) and an electrolyte (not shown), and a connecting portion provided on the upper side of the receiving portion and coupled with a cap assembly (130).

[0151] The above can (120) may be a general cylindrical battery can known in the art, and in this case, the lithium secondary battery according to the present invention may be a cylindrical battery. For example, the above can is a cylindrical container with an opening formed at one end, and is made of a conductive metal material such as aluminum or steel. An electrode assembly is housed in the inner space through the opening, and an electrolyte is injected. If necessary, a beading portion and a crimping portion may be provided at the top of the cylindrical can. The beading portion inhibits the movement of the electrode assembly housed inside the can and functions as a support portion on which a seal is seated, and may be formed by pressing the outer circumference of the cylindrical can to a certain depth.

[0152] The above-mentioned crimping part is intended to combine and seal a sealing body and a cylindrical can, and has an extended and folded shape to wrap around a portion of the upper surface of the sealing body.

[0153] The bottom surface of the above can (120) can be combined with the negative tab (112a) of the electrode assembly (110).

[0154]

[0155] Cap Assembly

[0156] The cap assembly (130) according to the present invention includes a cap plate and a sealing gasket that provides airtightness and insulation between the cap plate and the battery can, and, if necessary, may further include a connecting plate electrically and mechanically coupled to the cap plate. The cap plate is pressed onto a beading portion formed on the battery can and may be secured by a crimping portion.

[0157] The cap plate is a component made of a conductive metal material that covers the top opening of the battery can. The cap plate is electrically connected to the positive tab (111a) of the electrode assembly and is electrically insulated from the can (120) through a sealing gasket. Thus, the cap plate can function as a positive terminal of the secondary battery. The cap plate may have a formed protrusion that protrudes upward from its center, and the protrusion may come into contact with an external power source to allow current to be applied from the external power source.

[0158] Meanwhile, the cylindrical battery may further include a safety vent and / or a current interrupt device (CID) at the bottom of the cap plate as needed.

[0159] The safety vent serves to cut off the current or exhaust gas when the pressure inside the battery rises due to an abnormal current, and may be made of metal. The thickness of the safety vent may vary depending on the material and structure, and is not particularly limited as long as it can rupture and release gas, etc. when a certain high pressure is generated inside the battery, for example, it may be 0.2 to 0.6 mm.

[0160] A Current Interrupt Device (CID) is positioned below the safety vent and above the electrode assembly to electrically connect the electrode assembly and the safety vent. The Current Interrupt Device includes a CID filter that transmits current by contacting the safety vent and interrupts the current when high voltage occurs inside the battery can, and a CID gasket that spatially separates and insulates the CID filter and the safety vent, except for a portion of the area.

[0161]

[0162] In the lithium secondary battery according to the present invention as described above, the expansion rate of the positive electrode tab protection member and the negative electrode plate is adjusted to satisfy specific conditions, so that the compression phenomenon of the electrode assembly is minimized during high-rate charging. Specifically, in the lithium secondary battery according to the present invention, no lithium deposition is observed at the upper part of the electrode assembly when 100 cycles of charging and discharging are performed under 1.5C charging and 1.5C discharging conditions. As such, since the lithium deposition occurring at the upper part of the electrode assembly during high-rate charging is significantly reduced in the lithium secondary battery according to the present invention, the rapid charging performance is excellent, and the degradation of battery performance due to lithium deposition during rapid charging can be effectively prevented.

[0163]

[0164] A lithium secondary battery according to the present invention as described above can be used to manufacture a battery pack. The battery pack comprises an assembly of lithium secondary batteries electrically connected according to the present invention and a pack housing that accommodates the same, wherein the pack housing may include a busbar for electrically connecting the lithium secondary batteries, a cooling unit, an external terminal, etc. The battery pack may be mounted in a vehicle. The vehicle may be, for example, an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle. The vehicle includes a four-wheeled vehicle or a two-wheeled vehicle. In particular, the lithium secondary battery according to the present invention has high energy density and excellent rapid charging performance, so it can be usefully used as a battery for an electric vehicle.

[0165]

[0166] The present invention will be explained in more detail below through specific embodiments. However, the following embodiments are intended only to aid in understanding the present invention, and the scope of the present invention is not limited to these embodiments.

[0167]

[0168] Example 1

[0169] Cathode Plate Manufacturing

[0170] A cathode slurry was prepared by adding cathode active material : cathode conductive material : cathode binder to distilled water in a weight ratio of 97 : 1 : 2.

[0171] As the cathode active material of the cathode slurry, a Si-C composite and a graphite-based cathode active material were mixed in a weight ratio of 3:97, and as the graphite-based cathode active material, artificial graphite and natural graphite were mixed in a weight ratio of 50:50. Single-walled CNTs were used as the cathode conductive material. In addition, as the cathode binder, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed in a weight ratio of 1:1.

[0172] The cathodic loading on both sides of the copper current collector sheet is 12 mg / cm² 2 After applying the above cathode slurry, the sheet was dried and rolled, and then vacuum dried. At this time, the cathode slurry was not applied to both ends of the copper current collector sheet, and a cathode tab was welded to the uncoated area where the cathode slurry was not applied to manufacture a cathode plate.

[0173]

[0174] <Manufacturing of Anode Plates>

[0175] A cathode active material: cathode conductive material: cathode binder was added to N-methylpyrrolidone in a weight ratio of 96:2:2 to prepare a cathode slurry. LiNi was used as the cathode active material. 0.9 Co 0.05 Mn 0.05 O2 was used, and Super P was used as the anode conductive material. In addition, PVdF was used as the anode binder.

[0176] The anode loading amount on both sides of the aluminum current collector sheet is 24 mg / cm² 2 After applying the anode slurry as described above, the sheet was dried and rolled, and then vacuum dried. At this time, the anode slurry was not applied to the central part of the aluminum current collector sheet, an anode tab was welded to the uncoated part where the anode slurry was not applied, and a protective tape with a thickness of 50 μm was attached to the anode tab to manufacture an anode plate.

[0177]

[0178] Lithium secondary battery manufacturing

[0179] An electrode assembly was manufactured by interposing a separator between the positive and negative plates prepared as described above, stacking them in the order of separator / positive plate / separator / negative plate, and then winding them. Then, the electrode assembly was placed in a cylindrical battery can, the electrolyte was injected, the positive tab and negative tab were welded to the cap plate and the battery can, respectively, and then sealed to manufacture a lithium secondary battery.

[0180]

[0181] Example 2

[0182] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a protective tape with a thickness of 30 μm was attached to the positive tab during the manufacture of the positive plate.

[0183]

[0184] Example 3

[0185] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a Si-C composite and a graphite-based negative electrode active material were mixed in a weight ratio of 4.5 to 95.5 when manufacturing the negative electrode plate, and a protective tape with a thickness of 30 μm was attached to the positive electrode tab when manufacturing the positive electrode plate.

[0186]

[0187] Example 4

[0188] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a Si-C composite and a graphite-based negative electrode active material were mixed in a weight ratio of 5:95 when manufacturing the negative electrode plate, and a protective tape with a thickness of 30 μm was attached to the positive electrode tab when manufacturing the positive electrode plate.

[0189]

[0190] Comparative Example 1

[0191] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a Si-C composite and a graphite-based negative electrode active material were mixed and used in a weight ratio of 4:96 when manufacturing the negative electrode plate.

[0192]

[0193] Comparative Example 2

[0194] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a Si-C composite and a graphite-based negative electrode active material were mixed in a weight ratio of 5:95 when manufacturing the negative electrode plate.

[0195]

[0196] Comparative Example 3

[0197] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a Si-C composite and a graphite-based negative electrode active material were mixed in a weight ratio of 10:90 when manufacturing the negative electrode plate, and a protective tape with a thickness of 30 μm was attached to the positive electrode tab when manufacturing the positive electrode plate.

[0198]

[0199] Experimental Example 1: Measurement of Cathode Expansion Rate

[0200] The anode and cathode plates prepared according to Examples 1 to 4 and Comparative Examples 1 to 3 were each punched into sizes of 31 mm × 43 mm to produce two anode samples and three cathode samples. Among the cathode samples, two samples were prepared as single-sided cathode samples by removing the cathode composite layer from one side of the cathode current collector layer.

[0201] Then, an electrode assembly was manufactured by stacking the anode sample and the cathode sample in the order of separator / single-sided cathode / separator / double-sided anode / separator / double-sided cathode / separator / double-sided anode / separator / single-sided cathode / separator.

[0202]

[0203] The manufactured electrode assembly was placed inside a pouch case, an electrolyte was injected, and the case was sealed to manufacture a measuring cell, and the thickness t0 of the measuring cell was measured.

[0204] Then, the above-mentioned measuring cell was mounted on a jig and pressurized to 0.156 MPa, and then charged to 4.2 V under a 0.05 C cut-off condition. Once charging was complete, the measuring cell was removed from the jig, and the thickness t of the charged measuring cell was measured. The measured values ​​of t0 and t were substituted into the following equation (2) to measure the cathode expansion coefficient A. The measurement results are shown in [Table 1] below.

[0205] Equation (2): A={(t-t0) / t} ×100

[0206]

[0207] Cathode Expansion Rate A[%] Anode Tab Protective Film Thickness[㎛] X Example 1 3.450170 Example 2 3.530105 Example 3 5.530165 Example 4 6.230186 Comparative Example 14.850240 Comparative Example 26.450320 Comparative Example 3 13.430402

[0208] Experimental Example 2:

[0209] After charging the lithium secondary batteries prepared according to Examples 1 to 4 and Comparative Examples 1 to 3 at 40°C in CCCV mode with a maximum charging voltage of 4.25V and a 0.05C cut-off condition, and then discharging them for up to 100 cycles with one cycle defined as discharging to 2.5V in CCC mode at 1.5C, the lithium secondary batteries were disassembled to visually check for lithium deposition on the upper part of the electrode assembly, and the results are shown in Table 2 below. Cases where lithium deposition was observed were marked as O, and cases where lithium deposition was not observed were marked as X.

[0210] Lithium Precipitation Status Example 1X Example 2X Example 3X Example 4X Comparative Example 10 Comparative Example 20 Comparative Example 30

[0211] Through [Table 2] above, it can be confirmed that lithium secondary batteries of Examples 1 to 4, where X is 200 or less, did not exhibit lithium precipitation after high-rate charging and discharging, whereas lithium secondary batteries of Comparative Examples 1 to 3, where X exceeds 200, exhibited lithium precipitation after high-rate charging and discharging.

Claims

1. An electrode assembly having a structure formed by winding a laminated sheet comprising a positive plate and a negative plate laminated with a separator interposed therebetween, an electrolyte, a can containing the electrode assembly and the electrolyte, and a cap assembly sealing the opening of the can. The above positive plate comprises a positive current collector, a positive composite layer disposed on at least one surface of the positive current collector, a positive tab electrically connected to the positive current collector, and a positive tab protection member protecting the positive tab. A lithium secondary battery in which X, defined by the above equation (1), is 200 or less. Equation (1): X = A × B In the above equation (1), A is the expansion rate of the cathode plate defined by the following equation (2), and B is the thickness of the anode tab protection member measured in μm. 식 (2): A={(t-t0) / t} ×100 In the above equation (2), t is the thickness of the measurement cell measured by cutting the cathode plate and the anode plate into sizes of 31 mm × 43 mm to produce two anode samples and three cathode samples, removing the cathode composite layer placed on one side of the cathode current collector from two of the cathode samples to produce a single-sided cathode sample, then stacking them in the order of separator / single-sided cathode / separator / double-sided anode / separator / double-sided cathode / separator / double-sided anode / separator / single-sided cathode / separator to produce an electrode assembly, placing the produced electrode assembly in a pouch, injecting an electrolyte, and sealing to produce a measurement cell, then pressurizing the measurement cell to 0.156 MPa and charging it to 4.2 V under a 0.05 C cut-off condition, and then measuring the thickness of the measurement cell, and t0 is the thickness of the measurement cell measured before the pressurization and charging.

2. In Paragraph 1, A lithium secondary battery in which the expansion rate (A) of the negative plate defined by the above equation (2) is 2% to 10%.

3. In Paragraph 1, A lithium secondary battery in which the thickness (B) of the positive tab protection member is 10㎛ to 60㎛.

4. In Paragraph 1, A lithium secondary battery in which the positive tab is positioned in the center of the positive plate.

5. In Paragraph 1, Anode loading is 20 mg / cm² 2 Lithium secondary battery.

6. In Paragraph 1, A lithium secondary battery in which the above-mentioned positive composite layer comprises a positive active material having a bimodal particle size distribution.

7. In Paragraph 1, The above-mentioned positive active material includes large particles with an average particle size of 8㎛ to 20㎛ and small particles with an average particle size of less than 8㎛, and A lithium secondary battery in which the above-mentioned large particles and small particles each independently comprise a lithium nickel-based oxide represented by the following [Chemical Formula 1]. [Chemical Formula 1] Li x Ni a Co b M 1 c M 2 d O2 In the above [Chemical Formula 1], M 1 is one or more selected from Mn and Al, and M 2 ... comprises one or more selected from the group consisting of Zr, Y, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.90≤x≤1.1, 0.50≤a<1.0, 0 <b<0.5, 0<c<0.5, 0≤d≤0.1임.

8. In Paragraph 1, The above cathode plate comprises a cathode current collector, a cathode composite layer disposed on at least one surface of the cathode current collector, and a cathode tab electrically connected to the cathode current collector. A lithium secondary battery in which the above-mentioned negative electrode composite layer comprises a Si-C composite and a graphite-based negative electrode active material.

9. In Paragraph 8, A lithium secondary battery comprising the above Si-C composite and the above graphite-based negative electrode active material in a weight ratio of 3:97 to 20:

80.

10. In Paragraph 1, The cathode loading amount is 10 mg / cm² 2 Lithium secondary battery.

11. In Paragraph 1, A lithium secondary battery in which no lithium precipitation is observed at the upper part of the electrode assembly when the above lithium secondary battery is charged and discharged 100 times under conditions of 1.5C charging and 1.5C discharging at 40℃.

12. In Paragraph 1, The above lithium secondary battery is a cylindrical lithium secondary battery.