Negative electrode, method for preparing same, and lithium secondary battery comprising same

Abstract

The present invention relates to a negative electrode having excellent rapid charging performance and swelling characteristics, and a method for preparing same. The negative electrode of the present invention comprises a negative electrode mixture layer including a Si-based negative electrode active material and a carbon-based negative electrode active material, and the 85° glossiness of the surface of the negative electrode mixture layer in a fully discharged state after activation is 14 to 25.

Description

Anode, method for manufacturing the same, and lithium secondary battery comprising the same

[0001] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0190455, filed December 22, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an anode for a lithium secondary battery and a method for manufacturing the same, and more particularly, to an anode having excellent rapid charging performance and swelling characteristics and a method for manufacturing the same.

[0003] A lithium secondary battery is generally composed of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and negative electrode include an active material capable of intercalating and deintercalating lithium ions.

[0004] The electrode of a lithium secondary battery is manufactured by applying an electrode slurry containing an electrode active material, a conductive material, and a binder onto an electrode current collector, drying the slurry, and then rolling and vacuum-drying the electrode until it reaches a desired thickness.

[0005] With the recent increase in demand for electric vehicles and other devices, the demand for batteries with high energy density and rapid charging performance is increasing. Accordingly, active efforts are being made to apply Si-based anode active materials, which boast high theoretical capacity, rapid lithium-ion reaction rates, and superior rapid charging performance. However, Si-based anode active materials exhibit significant volume changes during charge / discharge, resulting in significant changes in anode thickness after activation and poor cycle life.

[0006] Conventional anodes using carbon-based anode active materials were designed by taking into account changes in electrode thickness before and after activation. However, when anodes using Si-based anode active materials are manufactured using the same method, the anode thickness increases significantly after activation, making it difficult to achieve the desired cell thickness. Furthermore, when the rolling ratio is increased in consideration of the increase in anode thickness after the activation process, excessive rolling can cause cracks in the anode active material or closure of pores on the electrode surface, leading to high-temperature side reactions and deterioration of rapid charging performance.

[0007] The present invention is intended to solve the above problems, and provides an anode including a Si-based anode active material as the anode active material, and manufactured so that the 85° glossiness of the anode surface after activation satisfies a specific range, thereby suppressing damage to the active material and blockage of pores on the electrode surface due to swelling and excessive rolling after activation, and a method for manufacturing the same.

[0008] In addition, the present invention seeks to provide a lithium secondary battery having excellent rapid charging performance and swelling characteristics, including the above-described negative electrode.

[0009] According to one embodiment, the present invention provides a negative electrode comprising a negative electrode composite layer including a Si-based negative electrode active material and a carbon-based negative electrode active material, and having an 85° glossiness of a negative electrode surface in a fully discharged state after activation of 14 to 25, preferably 14 to 20, more preferably 15 to 20.

[0010] The above Si-based negative electrode active material is SiOx (wherein, 0 <x<2), Si-C 복합체 또는 이들의 조합을 포함할 수 있으며, 특히 바람직하게는 Si-C 복합체일 수 있다.

[0011] The above carbon-based negative electrode active material may include artificial graphite, natural graphite, or a combination thereof, and preferably, may be a mixture of artificial graphite and natural graphite.

[0012] The above Si-based negative electrode active material and the above carbon-based negative electrode active material may be included in a weight ratio of 1:99 to 20:80, preferably 3:97 to 20:80, and more preferably 3:97 to 15:85.

[0013] Meanwhile, the 60° glossiness of the cathode surface in the fully discharged state after activation may be 0.1 to 4.0, preferably 0.5 to 4.0, more preferably 1.0 to 4.0.

[0014] The above cathode may have a curvature defined by the following equation (1) of 2 or less, preferably 1 to 2, and more preferably 1.2 to 2.0.

[0015] Equation (1): Curvature (τ) = L e / L0

[0016] In the above equation (1), L0 is the thickness of the cathode composite layer, and L e is the average movement distance of lithium ions inside the negative electrode composite layer.

[0017] The above cathode may have a cathode adhesion strength measured by a 90 degree peel test of 40 gf / 20 mm or more, preferably 40 gf / 20 mm to 70 gf / 20 mm, more preferably 45 gf / 20 mm to 70 gf / 20 mm.

[0018] According to another embodiment, the present invention provides a method for manufacturing a negative electrode, comprising the steps of: coating a negative electrode slurry including a silicon-based negative electrode active material and a carbon-based negative electrode active material on a negative electrode current collector; rolling the negative electrode coated with the negative electrode slurry so that the 85° gloss of the negative electrode surface in a fully discharged state after activation becomes 14 to 25, preferably 14 to 20, more preferably 15 to 20; and vacuum-drying the rolled negative electrode to form a negative electrode composite layer.

[0019] The above rolling can be performed so that the rolling ratio defined by the following equation (2) is 25% to 40%, preferably 25% to 35%.

[0020] Equation (2): Rolling ratio (%) = {(Cathode composite layer thickness before rolling - Cathode composite layer thickness after rolling) / Cathode composite layer thickness before rolling} × 100

[0021] The above rolling can be performed so that the porosity of the cathode composite layer after rolling is 30% to 40%, preferably 30% to 35%.

[0022] Meanwhile, the 85° glossiness of the surface of the cathode composite layer after the vacuum drying may be 14 to 20, preferably 14 to 18, more preferably 14 to 17, and the 60° glossiness of the surface of the cathode composite layer after the vacuum drying may be 1 to 5, preferably 2 to 5, more preferably 2.5 to 5.

[0023] According to another embodiment, the present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, and an electrolyte according to the present invention described above.

[0024] The negative electrode according to the present invention is manufactured so that the 85° glossiness of the negative electrode composite layer surface satisfies a specific range after activation, and although it includes a Si-based negative electrode active material that has a large volume change during charge and discharge as the negative electrode active material, swelling after activation is small, so that the cell thickness of a lithium secondary battery can be formed within a desired range, and the negative electrode can be effectively prevented from being degraded due to destruction of the conductive network caused by a change in the negative electrode thickness.

[0025] In addition, when the negative electrode is manufactured so that the 85° glossiness of the negative electrode composite layer surface after activation satisfies the scope of the present invention, damage to the active material and clogging of pores on the electrode surface due to excessive rolling are suppressed, thereby reducing side reactions with the electrolyte and improving rapid charging performance.

[0026] In addition, the negative electrode according to the present invention can suppress the delamination of the negative electrode composite layer during charge and discharge, thereby suppressing the reduction in lifespan due to the delamination of the negative electrode.

[0027] In addition, the negative electrode according to the present invention can realize high capacity by including a Si-based negative electrode active material with a large capacity as the negative electrode active material.

[0028] Therefore, when the negative electrode according to the present invention is applied to a lithium secondary battery, high energy density, excellent life characteristics, and rapid charging performance can be realized.

[0029] Figure 1 is a graph showing the results of a rapid charging performance experiment of a coin half cell using a cathode manufactured by an example and a comparative example.

[0030] Hereinafter, the present invention will be described in more detail.

[0031] In the present invention, "glossiness" is a value that quantifies the amount of light that is regularly reflected when light is irradiated onto the surface of a measurement target at a specific incident angle, and can be measured using a gloss meter such as BYK's Micro-Tri-Gloss (AG4563). 85° glossiness means glossiness when the incident angle of light is 85°, 60° glossiness means glossiness when the incident angle of light is 60°, and 20° glossiness means glossiness when the incident angle of light is 20°.

[0032] In the present invention, “curvature” is an indicator indicating the degree to which the internal path of the cathode composite layer is curved, and is a value defined by the following equation (1).

[0033] Equation (1): Curvature (τ) = L e / L0

[0034] In the above equation (1), L0 is the thickness of the cathode composite layer, and L e is the average movement distance of lithium ions inside the negative electrode composite layer, and the above L eIt is a value calculated by measuring the electrode pore resistance through AC impedance measurement after manufacturing a cell (symmetric cell) with a cathode / separator / cathode structure.

[0035] In the present invention, the “rolling rate” is a value defined by the following equation (2), and can be calculated by measuring the thickness of the cathode composite layer before and after rolling.

[0036] Equation (2): Rolling ratio (%) = {(Cathode composite layer thickness before rolling - Cathode composite layer thickness after rolling) / Cathode composite layer thickness before rolling} × 100

[0037] In the present invention, the “porosity” is the percentage of the volume of pores with respect to the total volume of the electrode composite layer, and is a value calculated by measuring the actual density of the electrode, dividing it by the theoretical electrode density, and then multiplying it by 100.

[0038] The inventors of the present invention have conducted repeated research to manufacture a lithium secondary battery having excellent capacity characteristics, life characteristics, and rapid charging performance, and as a result, have found that when an anode is manufactured such that the 85° glossiness of the anode composite layer after activation satisfies a specific range while including a Si-based anode active material as the anode active material, swelling after activation is reduced, the anode adhesiveness is excellent, and damage to the anode active material and the anode surface is minimized, thereby achieving the above-described purpose, and thus completing the present invention.

[0039]

[0040] cathode

[0041] First, the cathode according to the present invention will be described.

[0042] The negative electrode according to the present invention comprises a negative electrode composite layer including a Si-based negative electrode active material and a carbon-based negative electrode active material, and the 85° glossiness of the surface of the negative electrode composite layer in a fully discharged state after activation is 14 to 25, preferably 14 to 20, more preferably 15 to 20.

[0043] The 85° glossiness of the surface of the above-mentioned negative electrode composite layer is a value that quantifies the amount of light reflected when light is irradiated at an incident angle of 85° on the outermost surface of the negative electrode composite layer. The 85° glossiness value increases as the number of pores on the surface of the negative electrode composite layer decreases, and the 85° glossiness value decreases as the number of pores increases due to damage to the surface or active material. Therefore, the 85° glossiness can be used as an indicator of the state of pores and / or damage on the surface of the negative electrode composite layer.

[0044] According to the study of the present inventors, when the 85° gloss of the outermost surface of the negative electrode composite layer in the fully discharged state after the activation process satisfies the above range, the negative electrode swelling after activation is small, the negative electrode adhesion is excellent, the reduction of negative electrode surface pores due to rolling is small, and the pore uniformity is excellent. Specifically, when the 85° gloss of the negative electrode composite layer surface after the activation process is less than 14, the adhesive strength between the negative electrode current collector and the negative electrode composite layer is reduced, so that the negative electrode composite layer is easily peeled off or the negative electrode active material is desorbed during charge and discharge, which increases side reactions with the electrolyte and accelerates negative electrode degradation, resulting in a decrease in life characteristics. In addition, when the 85° gloss of the negative electrode composite layer surface after the activation process exceeds 25, the pores on the negative electrode composite layer surface are too small, so that the electrolyte mobility is low, and the curvature of the negative electrode composite layer increases, so that the lithium mobility is lowered, and as a result, lithium precipitation may occur during rapid charging.

[0045] Meanwhile, the negative electrode may have a 60° glossiness of the negative electrode composite layer surface in a fully discharged state after activation of 0.1 to 4.0, preferably 0.5 to 4.0, and more preferably 1.0 to 4.0. When the 60° glossiness of the negative electrode surface satisfies the above range, the rapid charging performance and negative electrode adhesion are further improved.

[0046]

[0047] The gloss of the cathode composite layer surface after activation varies depending on process conditions such as the composition of the cathode composite layer, drying conditions during cathode manufacturing, and rolling conditions. Therefore, by appropriately adjusting the composition of the cathode composite layer and the cathode manufacturing process conditions, a cathode having a desired gloss can be manufactured.

[0048]

[0049] Meanwhile, the negative electrode according to the present invention includes a negative electrode composite layer including a Si-based negative electrode active material and a carbon-based negative electrode active material, and the negative electrode composite layer may further include a negative electrode conductive material and a negative electrode binder in addition to the negative electrode active material.

[0050] The above Si-based negative electrode active material may be, for example, metal silicon (Si), silicon oxide (SiOx, where 0 <x<2), Si-C 복합체 및 Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님)로 이루어진 군으로부터 선택된 1종 이상을 포함할 수 있다. 상기 원소 Y로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, 및 이들의 조합으로 이루어진 군에서 선택될 수 있다. 바람직하게는 상기 Si계 음극 활물질은 SiO x(Here, 0 <x<2), Si-C 복합체 또는 이들의 조합을 포함할 수 있으며, 특히 바람직하게는 Si-C 복합체일 수 있다. Si-C 복합체는 금속 Si에 비해서는 충방전 시 부피 팽창 정도가 작고, SiOx에 비해 용량 특성 및 전기 전도성이 우수하다. 따라서, Si계 음극 활물질로 Si-C 복합체를 사용할 경우에 음극 부피 변화를 최소화면서 높은 용량을 구현할 수 있다.

[0051] Preferably, the Si-C composite may have a 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, the cell resistance characteristics and life characteristics are excellently improved.

[0052] In addition, the Si-C composite is D 50 This may be 1 ㎛ to 15 ㎛, preferably 2 ㎛ to 10 ㎛, more preferably 3 ㎛ to 10 ㎛. In addition, the Si-C composite may be D 10 This may be 5㎛ or less, preferably 1 to 5㎛, and D 90 This may be 6 µm to 20 µm, preferably 6 µm to 15 µm. When the particle size distribution of the Si-C composite satisfies the above range, the negative electrode density increases, thereby realizing high energy density.

[0053]

[0054] Meanwhile, the carbon-based negative electrode active material may be, for example, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, etc., and preferably may be artificial graphite, natural graphite, and a combination thereof, and particularly preferably may be a mixture of artificial graphite and natural graphite.

[0055] When the carbon-based negative electrode active material is a mixture of artificial graphite and natural graphite, the weight ratio of the artificial graphite to natural graphite may be 99:1 to 60:40, preferably 90:10 to 60:40, and more preferably 90:10 to 70:30. When the mixing ratio of artificial graphite and natural graphite satisfies the above range, both the life characteristics and the rapid charging performance are excellent.

[0056]

[0057] In the present invention, the Si-based negative electrode active material and the carbon-based negative electrode active material may be included in a weight ratio of 1:99 to 20:80, preferably 3:97 to 20:80, and more preferably 3:97 to 15:85. When the mixing ratio of the Si-based negative electrode active material and the carbon-based negative electrode active material satisfies the above range, both the capacity characteristics and the life characteristics are excellent.

[0058]

[0059] The above negative electrode active material may be included in an amount of 80 to 99 wt%, preferably 85 to 99 wt%, and more preferably 90 to 99 wt%, based on the total weight of the negative electrode composite layer.

[0060]

[0061] Meanwhile, the negative electrode conductive material is used to provide conductivity to the negative electrode, and can be used without any special restrictions as long as it is used as a conductive material for a lithium secondary battery. Specific examples of the negative electrode conductive material include carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotube; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these may be used alone or a mixture of two or more thereof. Preferably, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, carbon nanotube, or a combination thereof may be used as the negative electrode conductive material, and in terms of improving conductivity, it is more preferable to use a dot-shaped conductive material and a linear conductive material together. At this time, the dot-shaped conductive material is a material having a particle shape and having a dot-shaped contact form with the negative electrode active material, for example, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, etc., and the linear conductive material is a material having a line-shaped contact form with the negative electrode active material, for example, carbon fiber, carbon nanotube, etc.

[0062] The above-mentioned negative electrode conductive material may be included in an amount of typically 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode composite layer.

[0063]

[0064] Next, the negative electrode binder plays a role in improving the adhesion between negative electrode active material particles and the adhesive strength 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 any special restrictions. Specific examples of the negative electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used.

[0065] The above negative electrode binder may be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode composite layer.

[0066]

[0067] Meanwhile, the cathode according to the present invention may have a curvature defined by the following equation (1) of 2 or less, preferably 1 to 2, and more preferably 1.2 to 2.0.

[0068] Equation (1): Curvature (τ) = L e / L0

[0069] In the above equation (1), L0 is the thickness of the cathode composite layer, and L e is the average movement distance of lithium ions inside the negative electrode composite layer, and the above L e It is a value calculated by measuring the electrode pore resistance through AC impedance measurement after manufacturing a cell (symmetric cell) with a cathode / separator / cathode structure.

[0070] When the cathode curvature satisfies the above range, lithium mobility within the cathode composite layer is improved, resulting in a more excellent effect of improving rapid charging performance.

[0071] The cathode curvature varies depending on process conditions such as the composition of the cathode composite layer and rolling conditions. Therefore, by appropriately controlling the composition of the cathode composite layer and the cathode manufacturing process conditions, a cathode having a desired curvature can be manufactured.

[0072]

[0073] In addition, the negative electrode according to the present invention has an excellent negative electrode adhesion strength of 40 gf / 20 mm or more, preferably 40 gf / 20 mm to 70 gf / 20 mm, and more preferably 45 gf / 20 mm to 70 gf / 20 mm, as measured by a 90-degree peel test. When the negative electrode adhesion strength satisfies the above range, negative electrode detachment is prevented during charging and discharging of a lithium secondary battery, thereby realizing excellent life characteristics.

[0074]

[0075] Method for manufacturing cathode

[0076] Next, a method for manufacturing a cathode according to the present invention will be described.

[0077] The method for manufacturing a negative electrode according to the present invention comprises the steps of (1) coating a negative electrode slurry containing a silicon-based negative electrode active material and a carbon-based negative electrode active material on a negative electrode current collector; (2) activating the negative electrode coated with the negative electrode slurry and then rolling the negative electrode so that the 85° glossiness of the surface of the negative electrode composite layer becomes 14 to 25; and (3) vacuum drying the rolled negative electrode to form a negative electrode composite layer.

[0078]

[0079] Hereinafter, each step of the method for manufacturing a cathode according to the present invention will be described in more detail.

[0080]

[0081] (1) Cathode slurry coating step

[0082] First, the cathode slurry is applied onto the cathode current collector and then dried to coat it.

[0083] At this time, as the negative electrode collector, negative electrode collectors generally used in the relevant technical field can be used, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. The negative electrode collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode collector, fine unevenness can be formed on the surface of the collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0084] Meanwhile, the negative electrode slurry can be manufactured by adding and mixing the components of the negative electrode composite layer according to the present invention, i.e., the negative electrode active material, the negative electrode conductive material, and the negative electrode binder, into a solvent, and at this time, the negative electrode active material includes a Si-based negative electrode active material and a carbon-based negative electrode active material. Since the Si-based negative electrode active material, the carbon-based negative electrode active material, the negative electrode conductive material, and the negative electrode binder are the same as those described above, a detailed description thereof will be omitted.

[0085] Meanwhile, the solvent used for cathode slurry in the relevant technical field may be any solvent, and the type thereof is not particularly limited. Specific examples of the solvent include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, or mixtures thereof.

[0086] The application of the above cathode slurry can be performed using slurry application methods known in the art, such as bar coating, slit coating, spray coating, etc.

[0087] Meanwhile, the drying is performed to remove the solvent in the negative electrode slurry and may be performed at 70 to 150°C, preferably 80 to 130°C, and the drying speed may be 5 m / min to 100 m / min, preferably 10 m / min to 90 m / min. When the drying temperature and drying speed satisfy the above ranges, the surface gloss of the negative electrode composite layer after activation can be easily controlled within the range of the present invention. Specifically, if the drying temperature is too high or the drying speed is too low, the rollability may deteriorate and the surface gloss of the negative electrode composite layer may decrease below a desired range, and if the drying temperature is too low or the drying speed is too fast, the solvent in the negative electrode slurry may not be sufficiently removed, excessive rolling may occur, and the surface gloss of the negative electrode composite layer may increase beyond a desired range.

[0088]

[0089] (2) Rolling stage

[0090] Next, the cathode coated with the cathode slurry manufactured through the above process is rolled.

[0091] At this time, the rolling can be performed so that the rolling ratio defined by the following equation (2) is 25% to 40%, preferably 25% to 35%, and more preferably 27% to 35%.

[0092] Equation (2): Rolling ratio (%) = {(Cathode composite layer thickness before rolling - Cathode composite layer thickness after rolling) / Cathode composite layer thickness before rolling} × 100

[0093] When the rolling rate satisfies the above range, the surface gloss of the negative electrode composite layer after activation is formed within the range of the present invention, and the negative electrode adhesion and rapid charging performance are excellent. Specifically, when the rolling rate is less than 25%, the surface gloss of the negative electrode composite layer after activation is below the range of the present invention, and the adhesive force between the negative electrode current collector and the negative electrode composite layer is reduced, which may result in a deterioration in the life characteristics. In addition, when the rolling rate exceeds 40%, the surface gloss of the negative electrode composite layer after activation exceeds the range of the present invention, and the negative electrode swelling increases after activation, and the rapid charging performance may be deteriorated due to a decrease in pores on the surface of the negative electrode composite layer.

[0094]

[0095] Meanwhile, the rolling may be performed so that the porosity of the negative electrode composite layer after rolling becomes 30% to 40%, preferably 30% to 35%. Conventionally, it was common to perform rolling so that the porosity of the negative electrode composite layer was 18% to 30% during the manufacture of negative electrodes. However, according to the research of the inventors of the present invention, in the case of a negative electrode including a Si-based negative electrode active material, particularly a Si-C composite, when rolling so that the porosity becomes 30% or less, the surface pores due to rolling are reduced and the pore uniformity is low, which causes significant swelling after activation. Therefore, in the present invention, by performing rolling so that the porosity of the negative electrode composite layer after rolling becomes 30% or more, swelling after activation can be reduced.

[0096]

[0097] (3) Vacuum drying stage

[0098] Next, the rolled cathode is vacuum-dried to form a cathode composite layer.

[0099] The above vacuum drying is intended to remove moisture remaining inside the cathode composite layer, and can be performed, for example, at a temperature of 100 to 150°C, preferably 110 to 130°C, for 5 to 20 hours, preferably 6 to 15 hours.

[0100] After the vacuum drying, the 85° glossiness of the surface of the negative electrode composite layer may be 14 to 20, preferably 14 to 18, more preferably 14 to 17, and the 60° glossiness may be 1 to 5, preferably 2 to 5, more preferably 2.5 to 5. In addition, the 20° glossiness of the surface of the negative electrode composite layer may be 0.2 to 0.7, preferably 0.3 to 0.7, more preferably 0.4 to 0.7. When the surface glossiness of the negative electrode composite layer after the vacuum drying satisfies the above range, the surface glossiness of the negative electrode composite layer after activation may be formed within the range of the present invention.

[0101]

[0102] lithium secondary battery

[0103] Next, a lithium secondary battery according to the present invention will be described.

[0104] A lithium secondary battery according to the present invention comprises a negative electrode, a positive electrode, and an electrolyte, and may further comprise a separator as needed. Since the negative electrode is identical to the negative electrode according to the present invention described above, a detailed description thereof will be omitted, and the remaining components excluding the negative electrode will be described below.

[0105]

[0106] anode

[0107] The positive electrode according to the present invention comprises a positive electrode composite layer comprising a positive electrode active material, a positive electrode conductive material, and a positive electrode binder. The positive electrode can be manufactured by coating a positive electrode slurry comprising a positive electrode active material, a positive electrode binder, a positive electrode conductive material, a solvent, etc. on a positive electrode current collector, and then rolling the coating to form a positive electrode composite layer.

[0108]

[0109] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used.

[0110]

[0111] The above-mentioned positive electrode 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 may be a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese 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 Z1O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(wherein, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (wherein, 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 )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 atomic fractions of independent elements, respectively, such that 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc.), and one or more compounds of these may be included.

[0112] Specifically, the positive electrode active material may include a lithium transition metal oxide represented by the following [chemical formula 1].

[0113] [Chemical Formula 1]

[0114] Li x Ni a Co b M 1 c M 2 d O2

[0115] In the above chemical formula 1, the M 1 is at least one selected from Mn and Al, and may preferably be Mn or a combination of Mn and Al from the viewpoint of durability.

[0116] M 2It may be at least one selected from the group consisting of Zr, Y, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S.

[0117] 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.

[0118] The above a represents the atomic fraction of nickel among the metal elements excluding lithium in the lithium transition metal oxide, and may be 0.50≤a<1.0, 0.60≤a≤0.95, 0.65≤a≤0.95, or 0.80≤a≤0.95. When the nickel content satisfies the above range, high-capacity characteristics can be realized.

[0119] The above b represents the atomic fraction of cobalt among the metal elements excluding lithium in the lithium transition metal oxide, 0 <b<0.5, 0<b<0.4, 또는 0.01≤b≤0.3일 수 있다.

[0120] The above c is M among the metal elements excluding lithium in the lithium transition metal oxide. 1 It represents the atomic fraction of , 0 <c<0.5, 0<c<0.4, 또는 0.01≤c≤0.3일 수 있다.

[0121] The above d is M among the metal elements excluding lithium in the lithium transition metal oxide. 2 It represents the atomic fraction of , and can be 0≤d≤0.1, or 0≤d≤0.05.

[0122] The above positive electrode active material may be included in an amount of 60 to 99 wt%, preferably 70 to 99 wt%, and more preferably 80 to 98 wt%, based on the total weight of the positive electrode composite layer.

[0123]

[0124] The above positive electrode binder is a component that assists in the bonding of the positive electrode active material and the positive electrode conductive material and the bonding to the current collector.

[0125] Examples of such positive binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluoroelastomer, and various copolymers.

[0126] Typically, the positive electrode binder may be included in an amount of 1 to 20 wt%, preferably 1 to 15 wt%, and more preferably 1 to 10 wt%, based on the total weight of the positive electrode composite layer.

[0127] The above-mentioned positive electrode conductive material is a component for further improving the conductivity of the positive electrode active material, and is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

[0128] Typically, the positive electrode conductive material may be included in an amount of 1 to 20 wt%, preferably 1 to 15 wt%, and more preferably 1 to 10 wt%, based on the total weight of the positive electrode composite layer.

[0129]

[0130] The solvent for the positive electrode slurry may include an organic solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), or acetone, and may be used in an amount that provides a desirable viscosity when including the positive electrode active material, positive electrode binder, and positive electrode conductive material. For example, the positive electrode active material, and optionally the positive electrode binder and positive electrode conductive material, may be included so that the concentration of the solid content is 50 to 95 wt%, preferably 70 to 95 wt%, and more preferably 70 to 90 wt%.

[0131]

[0132] electrolyte

[0133] The electrolyte used in the present invention may include various electrolytes that can be used in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, and the type thereof is not particularly limited.

[0134] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0135] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may 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.

[0136] 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, LiB(C2O4)2, or a combination thereof. 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.

[0137] Meanwhile, in addition to the above 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. For example, the electrolyte may include at least one additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

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

[0139] An example of the above halogen-substituted carbonate compound is fluoroethylene carbonate (FEC).

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

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

[0142] Examples of the above phosphate compound include at least one compound selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyl trimethyl silyl phosphate, trimethyl silyl phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl) phosphite.

[0143] Examples of the above borate compounds include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), and lithium bisoxalatoborate (LiB(C2O4)2, LiBOB).

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

[0145] An example of the benzene compound may include fluorobenzene, an example of the amine compound may include triethanolamine or ethylenediamine, and an example of the silane compound may include tetravinylsilane.

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

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

[0148]

[0149] membrane

[0150] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions. Specifically, the separator may be a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may also be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength.

[0151]

[0152] The lithium secondary battery according to the present invention as described above can be used to manufacture a battery pack. The battery pack includes an assembly of lithium secondary batteries according to the present invention electrically connected and a pack housing that accommodates the assembly. The pack housing can include a bus bar for electrically connecting the lithium secondary batteries, a cooling unit, an external terminal, etc. The battery pack can be mounted on a vehicle. The vehicle can be, for example, an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle. The vehicle includes a four-wheel vehicle or a two-wheel vehicle. In particular, the lithium secondary battery according to the present invention has a high energy density and excellent rapid charging performance, and thus can be usefully used as a battery for an electric vehicle.

[0153]

[0154] Hereinafter, the present invention will be described in more detail through specific examples. However, the following examples are provided solely to aid understanding of the present invention and are not intended to limit the scope of the present invention to these examples.

[0155]

[0156] Example 1

[0157] A negative electrode slurry was prepared by adding negative electrode active material: negative electrode conductive material: negative electrode binder to distilled water at a weight ratio of 97:1:2.

[0158] At this time, the negative electrode active material was used by mixing Si-C composite: artificial graphite: natural graphite in a weight ratio of 5:76:19, and the negative electrode conductive material was used by mixing carbon black: single-walled carbon nanotube in a weight ratio of 97:3.

[0159] In addition, as the negative electrode binder, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed in a weight ratio of 60:40 and used.

[0160] After applying the above-mentioned negative electrode slurry on a copper current collector, the negative electrode was manufactured by drying it under the conditions of a drying temperature of 120°C and a drying speed of 10 m / min, rolling it at a rolling ratio of 27%, and vacuum drying it.

[0161]

[0162] Example 2

[0163] A cathode was manufactured in the same manner as in Example 1, except that rolling was performed at a rolling ratio of 35%.

[0164]

[0165] Example 3

[0166] After applying the above-mentioned negative electrode slurry on a copper current collector, a negative electrode was manufactured in the same manner as in Example 1, except that drying was performed at a drying temperature of 130°C and a drying speed of 40 m / min.

[0167]

[0168] Example 4

[0169] A negative electrode was manufactured in the same manner as in Example 1, except that the negative electrode active material was a mixture of Si-C composite: artificial graphite: natural graphite in a weight ratio of 10:70:20 when manufacturing the negative electrode slurry.

[0170]

[0171] Comparative Example 1

[0172] A cathode was manufactured in the same manner as in Example 1, except that rolling was performed at a rolling ratio of 45%.

[0173]

[0174] Comparative Example 2

[0175] A cathode was manufactured in the same manner as in Example 1, except that rolling was performed at a rolling ratio of 20%.

[0176]

[0177] Comparative Example 3

[0178] A cathode was manufactured in the same manner as in Example 1, except that rolling and vacuum drying were not performed.

[0179]

[0180] Comparative Example 4

[0181] After applying the above-mentioned negative electrode slurry on a copper current collector, a negative electrode was manufactured in the same manner as in Example 1, except that drying was performed at a drying temperature of 90°C and a drying speed of 70 m / min.

[0182]

[0183] Comparative Example 5

[0184] A negative electrode was manufactured in the same manner as in Example 1, except that artificial graphite and natural graphite were mixed in a weight ratio of 80:20 as the negative electrode active material when manufacturing the negative electrode slurry.

[0185]

[0186] Experimental Example 1: Measurement of cathodic gloss and waviness after V / D

[0187] The surface gloss and curvature of the negative electrode composite layer manufactured by the above examples and comparative examples were measured by the following methods.

[0188] (1) Gloss (unit: GU): Measured using BYK’s Micro-Tri-Gloss (AG4563) according to the ISO2813 method.

[0189] (2) Flexural strength (τ): An electrode assembly was manufactured by assembling two negative electrodes with a separator between them, placing the electrode assembly in a battery case, injecting an electrolyte (ethylene carbonate: ethyl methyl carbonate = 3:7 v / v%) that does not contain a lithium salt, and aging for 12 to 24 hours to manufacture a symmetrical coin cell. Then, a current of 0.1 to 1,000,000 Hz and 10 Mv was applied to the manufactured symmetrical coin cell, and the electrode pore resistance was measured using a graph measured by EIS (Electrochemical Impedance Spectroscopy) to obtain the average movement distance L of lithium ions inside the negative electrode composite layer. e The curvature was calculated by dividing it by the thickness of the cathode composite layer L0. The measurement results are shown in [Table 1] below.

[0190]

[0191] Cathode gloss Cathode curvature 20°60°85°Example 10.53.814.71.3Example 20.64.0161.5Example 30.64.116.21.5Example 40.74.517.11.7Comparative example 10.85.621.12.6Comparative example 20.32.2121.2Comparative example 30.10.62.2Not measurableComparative example 40.32.119.31.2Comparative example 52.811.149.02.58

[0192] Experimental Example 2: Measurement of cathodic gloss after activation

[0193] A cathode slurry was prepared by adding cathode active material: conductive material: binder in a weight ratio of 97:1:2 to N-methyl pyrrolidone.

[0194] At this time, lithium nickel cobalt manganese oxide was used as the positive electrode active material, carbon black was used as the positive electrode conductive material, and polyvinylidene fluoride (PVdF) was used as the positive electrode binder.

[0195] After applying the above positive electrode slurry on an aluminum current collector, the positive electrode was manufactured by drying at a drying temperature of 110°C and a drying speed of 10 m / min, rolling at a rolling ratio of 30%, and vacuum drying.

[0196] An electrode assembly was manufactured by interposing a separator between the positive electrode manufactured as described above and each negative electrode manufactured in the examples and comparative examples, and then the electrode assembly was placed in a battery case and an electrolyte was injected to manufacture a lithium secondary battery cell.

[0197] The above lithium secondary battery cell was aged at 25°C for 360 minutes, then charged to 4.45 V at 0.1C and aged at 40°C to perform an activation process.

[0198] The lithium secondary battery cell, for which the above activation process was completed, was discharged to SOC 0, then disassembled to separate the negative electrode, and the glossiness of the negative electrode composite layer surface and the negative electrode adhesive strength were measured using the following method.

[0199] (1) Gloss (unit: GU): Measured using BYK’s Micro-Tri-Gloss (AG4563) according to the ISO2813 method.

[0200] (2) Negative adhesion (unit: gf / 20mm): Using a universal tensile tester (UTM), the force required to separate the negative electrode composite layer from the negative electrode current collector was measured while pulling the negative electrode composite layer at a peeling angle of 90 degrees and a peeling speed of 100 mm / min.

[0201]

[0202] The measurement results are shown in [Table 2] below.

[0203] After activation, cathodic gloss, cathodic adhesion [g / 20mm], 20°, 60°, 85°, Example 10.3, 2.0, 16.75°, Example 20.6, 3.5, 18.36°, Example 30.6, 3.4, 19.15°, Example 40.6, 3.1, 17.34°, Comparative Example 10.4, 3.4, 26.66°, Comparative Example 20.3, 1.9, 12.53°, Comparative Example 3, Not measurable, Not measurable, Not measurable, Comparative Example 5, 40.3, 1.8, 12.10°, Comparative Example 5, 1.16, 14.922°, Comparative Example 5

[0204] Through the above [Table 2], it can be confirmed that the cathodes of Examples 1 to 4, which have an 85° gloss of 14 to 25 on the cathode surface in a fully discharged state after activation, exhibit a high cathode adhesive strength of 45 gf / 20 mm or more.

[0205] In comparison, the negative electrodes of Comparative Examples 2 to 4, in which the 85° gloss of the negative electrode surface was less than 14 in the fully discharged state after activation, exhibited low negative electrode adhesive strength of less than 40 gf / 20 mm. On the other hand, in the case of the negative electrode of Comparative Example 1, in which the 85° gloss of the negative electrode surface was more than 25 in the fully discharged state after activation, the adhesive strength was excellent, but the rapid charging performance was significantly poor, as described below.

[0206] In addition, the negative electrode of Comparative Example 5, which used only a carbon-based negative electrode active material without using a Si-based negative electrode active material, had an 85° glossiness of more than 25 on the negative electrode surface in the fully discharged state after activation, and the negative electrode adhesive strength was low at 22 gf / 20 mm.

[0207]

[0208] Experimental Example 3: Rapid Charging Performance Evaluation

[0209] An electrode assembly was manufactured by interposing a separator between the negative electrode and the lithium counter electrode manufactured in Examples 1 to 4 and Comparative Examples 1, 2, 4 and 5, and the electrode assembly was placed in a battery case and an electrolyte was injected to manufacture a coin-half cell.

[0210] The above coin half-cell was charged in 3.0C, CC mode to obtain a charge profile according to SOC, and the inflection point in the charge profile was evaluated as the point at which lithium precipitation occurs. The evaluation results are shown in Fig. 1.

[0211] As shown in Fig. 1, in the case of the batteries using the negative electrodes of Examples 1 to 4, lithium plating occurred at SOC 40 or higher, whereas in the case of the batteries using the negative electrodes of Comparative Examples 1, 4, and 5, lithium plating occurred at SOC 20 to 30, and it was confirmed that the rapid charging performance was inferior.

Claims

1. A negative electrode composite layer including a Si-based negative electrode active material and a carbon-based negative electrode active material, A cathode having an 85° glossiness of 14 to 25 on the surface of the cathode composite layer in the fully discharged state after activation.

2. In paragraph 1, The above Si-based negative electrode active material is SiOx (wherein, 0 <x<2), Si-C 복합체 또는 이들의 조합을 포함하고, The above carbon-based negative electrode active material is a negative electrode including artificial graphite, natural graphite or a combination thereof.

3. In paragraph 1, The above Si-based negative electrode active material is a Si-C composite, The above carbon-based negative electrode active material is a negative electrode which is a mixture of artificial graphite and natural graphite.

4. In paragraph 1, An anode wherein the Si-based anode active material and the carbon-based anode active material are included in a weight ratio of 1:99 to 20:

80.

5. In paragraph 1, The above cathode is a cathode having a 60° glossiness of 0.1 to 4.0 on the surface of the cathode composite layer in a fully discharged state after activation.

6. In paragraph 1, The above cathode is a cathode having a curvature of 2 or less, as defined by the following equation (1). Equation (1): Curvature (τ) = L e / L0 In the above equation (1), L0 is the thickness of the cathode composite layer, and L e is the average movement distance of lithium ions inside the negative electrode composite layer.

7. In paragraph 1, The above negative electrode is a negative electrode having a negative electrode adhesion of 40 gf / 20 mm or more as measured by a 90-degree peel test.

8. A step of coating a negative electrode slurry including a silicon-based negative electrode active material and a carbon-based negative electrode active material on a negative electrode current collector; A step of rolling the cathode coated with the above cathode slurry so that the 85° glossiness of the cathode composite layer surface becomes 14 to 25 in the fully discharged state after activating the cathode; and A method for manufacturing a cathode, comprising the step of vacuum drying the rolled cathode to form a cathode composite layer.

9. In paragraph 8, A method for manufacturing a cathode, wherein the above rolling is performed so that the rolling ratio defined by the following equation (2) is 25% to 40%. Equation (2): Rolling ratio (%) = {(Cathode composite layer thickness before rolling - Cathode composite layer thickness after rolling) / Cathode composite layer thickness before rolling} × 100 10. In paragraph 8, A method for manufacturing a cathode, wherein the above rolling is performed so that the porosity of the cathode composite layer is 30% to 40%.

11. In paragraph 8, A method for manufacturing a cathode having an 85° glossiness of 14 to 20 on the surface of the cathode composite layer after the vacuum drying.

12. In paragraph 8, A method for manufacturing a cathode having a 60° glossiness of 1 to 5 on the cathode surface after the vacuum drying.

13. A lithium secondary battery comprising a negative electrode according to any one of claims 1 to 7; a positive electrode; and an electrolyte.

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