Secondary battery

Abstract

A secondary battery according to an embodiment of the present invention includes an electrode assembly including a positive electrode, a negative electrode disposed opposite the positive electrode, and a separator disposed between the positive electrode and the negative electrode, the electrode assembly being wound around a winding core. The positive electrode includes a positive electrode current collector having a first surface and a second surface opposed to each other, a first positive electrode active material layer disposed on the first surface, and a second positive electrode active material disposed on the second surface. And the load capacity difference value between the first positive active material layer and the second positive active material layer and the diameter of the roll core meet a preset relation.

Description

Technical Field

[0001] This invention relates to a secondary battery. Background Technology

[0002] A rechargeable battery is a type of battery that can be repeatedly charged and discharged. With the rapid development of information and communication technologies and the display industry, rechargeable batteries have been widely used in various portable electronic communication devices, such as portable cameras, mobile phones, and laptops, as their power source. Recently, battery packs incorporating rechargeable batteries have been developed and are being used as a power source for environmentally friendly vehicles such as electric vehicles and hybrid vehicles.

[0003] Examples of rechargeable batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium-ion batteries have advantages in terms of high operating voltage and high energy density per unit weight, as well as fast charging speed and lightweight design. Therefore, lithium-ion batteries have been actively developed and applied in various industrial fields.

[0004] In recent years, with the continuous expansion of the application range of lithium-ion rechargeable batteries, there is a growing demand for rechargeable batteries with higher stability and reliability. For example, during repeated charging and discharging of rechargeable batteries, components such as lithium may precipitate, which can reduce the long-term durability of the battery. Therefore, there is a need in the art to address the problems related to lithium precipitation during the charging and discharging of rechargeable batteries, thereby improving their capacity and lifespan. Summary of the Invention

[0005] According to one aspect of the invention, an object of the invention is to provide a secondary battery that exhibits improved stability and operational reliability by preventing lithium precipitation during charging / recharging cycles.

[0006] A secondary battery according to an embodiment of the present invention includes an electrode assembly comprising a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separator disposed between the positive and negative electrodes, the electrode assembly being wound around a winding core. The positive electrode includes: a positive current collector comprising a first surface and a second surface opposite to each other; a first positive active material layer disposed on the first surface; and a second positive active material layer disposed on the second surface.

[0007] The secondary battery satisfies the following equation 1.

[0008] [Equation 1]

[0009] Y = AX 2 - BX + C

[0010] In Equation 1, X represents the diameter of the core, and Y represents the loading amount gap as defined by Equation 2 below, where A is 0.0062 to 0.013, B is 0.1242 to 0.2622, and C is 0.943 to 1.9907.

[0011] [Equation 2]: Load difference (mg / cm³) 2 = LW2 - LW1

[0012] In Equation 2, LW1 represents the loading amount (mg / cm³) of the first positive electrode active material layer. 2 LW2 represents the loading amount (mg / m²) of the second positive electrode active material layer. 2 ).

[0013] In some implementations, the first positive electrode active material layer may be closer to the core than the second positive electrode active material.

[0014] In some implementations, X in Equation 1 can be 3mm to 8mm.

[0015] In some implementations, the loading difference can be 0.3 mg / cm³. 2 Up to 1.1 mg / cm 2 .

[0016] In some implementations, the loading difference can be 0.45 mg / cm³. 2 Up to 0.8 mg / cm 2 .

[0017] In some implementations, LW1 in Equation 2 can be 7.6 mg / cm³. 2 Up to 49.6 mg / cm 2 .

[0018] In some implementations, LW2 in Equation 2 can be 8 mg / cm³. 2 Up to 50 mg / cm 2 .

[0019] In some implementations, the overall density of the first positive electrode active material layer and the second positive electrode active material can be 3.2 g / cm³. 3 Up to 3.8 g / cm 3 .

[0020] In some implementations, the average value of LW1 and LW2 in Equation 2 can be 16 mg / cm³. 2 Up to 30 mg / cm 2 .

[0021] In some embodiments, the secondary battery may also include a case housing the electrode assembly. In some embodiments, the case may have a cylindrical shape.

[0022] In some implementations, the electrode assembly may include a jelly roll structure that is repeatedly wound around a core.

[0023] According to one embodiment of the present invention, precipitation of internal positive electrode material (e.g., lithium) can be prevented.

[0024] According to one embodiment of the present invention, the cycle life characteristics of a secondary battery can be improved.

[0025] The secondary battery of this invention can be widely used in green technology fields, such as electric vehicles, battery charging stations, and solar and wind power generation using batteries. The secondary battery of this invention can be used in environmentally friendly electric vehicles, hybrid vehicles, etc., aiming to mitigate climate change by reducing air pollution and greenhouse gas emissions. Attached Figure Description

[0026] The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 This is a schematic cross-sectional view showing the positive electrode for a secondary battery according to an exemplary embodiment;

[0028] Figure 2 and Figure 3 These are schematic plan views and cross-sectional views of a secondary battery according to an exemplary embodiment;

[0029] Figure 4 This is a graph showing Equation 1; and

[0030] Figure 5 This is a schematic cross-sectional view showing the negative electrode according to an exemplary embodiment. Detailed Implementation

[0031] According to an exemplary embodiment, a secondary battery is provided.

[0032] Embodiments of the present invention will be described in detail below. However, these embodiments are merely examples, and the present invention is not limited to the specific embodiments described as examples.

[0033] Figure 1 This is a schematic cross-sectional view showing the positive electrode for a secondary battery according to an exemplary embodiment.

[0034] refer to Figure 1 The positive electrode 110 may include a positive electrode current collector 112, a first positive electrode active material layer 114, and a second positive electrode active material layer 116.

[0035] The positive current collector 112 may comprise stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive current collector 112 may also comprise aluminum or stainless steel with a surface treated with carbon, nickel, titanium, or silver. For example, the positive current collector 112 may have a thickness of 10-50 μm.

[0036] The positive current collector 112 may include a first surface 112a and a second surface 112b that are opposite to each other.

[0037] The first positive electrode active material layer 114 can be disposed on the first surface 112a of the positive electrode current collector 112, and the second positive electrode active material layer 116 can be disposed on the second surface 112b.

[0038] In one embodiment, the first positive electrode active material layer 114 can be directly disposed on the first surface 112a.

[0039] In one embodiment, the second positive electrode active material layer 116 can be directly disposed on the second surface 112b.

[0040] In some implementations, the positive electrode 110 can be bent along the direction surrounding the imaginary winding center WC.

[0041] For example, the first positive electrode active material layer 114 may be closer to the winding center WC and / or the core 50 than the second positive electrode active material layer 116. For example, the winding center WC may represent the core 50 of the secondary battery.

[0042] The following will be referenced Figure 2 and Figure 3 Describe the detailed structure of a secondary battery.

[0043] In an exemplary embodiment, the first positive electrode active material layer 114 and the second positive electrode active material layer 116 may each include a positive electrode active material.

[0044] For example, the positive electrode active material may include lithium-nickel metal oxide. Lithium-nickel metal oxide may also include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0045] In some embodiments, the positive electrode active material or lithium-nickel metal oxide may include a layered structure or a crystal structure represented by Formula 1 below.

[0046] [Formula 1]

[0047] Li x Nia M b O 2+z

[0048] In Equation 1, x, a, b, and z can satisfy 0.9 ≤ x ≤ 1.2, 0.5 ≤ a ≤ 0.99, 0.01 ≤ b ≤ 0.5, and -0.5 ≤ z ≤ 0.1. As mentioned above, M can include Co, Mn, and / or Al.

[0049] The chemical structure represented by Formula 1 indicates the bonding relationship between elements contained in the layered or crystal structure of the positive electrode active material, and does not exclude other additional elements. For example, M may include Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active elements of the positive electrode active material. Here, it should be understood that Formula 1 is provided to represent the bonding relationship between the main active elements, and Formula 1 is a formula that includes the introduction and substitution of additional elements.

[0050] In one embodiment, the positive electrode active material may further include an auxiliary element added to the main active element to enhance its chemical stability or layered / crystal structure. The auxiliary element may be bonded together with the main active element into the layered / crystal structure to form bonds, and it should be understood that this also includes the chemical structures represented by Formula 1.

[0051] Auxiliary elements may include at least one of the following: Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. Auxiliary elements such as Al can act as auxiliary active elements, working together with Co or Mn to contribute to the capacity / output activity of the positive electrode active material.

[0052] For example, positive electrode active materials or lithium-nickel metal oxides may include layered or crystalline structures represented by Formula 1-1.

[0053] [Equation 1-1]

[0054] Li x Ni a M1 b1 M2 b2 O 2+z

[0055] In Equation 1-1, M1 may include Co, Mn and / or Al. M2 may include the aforementioned auxiliary elements. In Equation 1-1, x, a, b1, b2 and z may satisfy 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b1+b2≤0.5, and -0.5≤z≤0.1.

[0056] In addition to boron as mentioned above, the positive electrode active material may also include coating elements or doping elements. For example, elements that are substantially the same as or similar to the auxiliary elements mentioned above can be used as coating elements or doping elements. For example, the aforementioned elements can be used alone or in combination of two or more as coating elements or doping elements.

[0057] The coating elements or doping elements may exist on the surface of lithium-nickel metal oxide particles or may penetrate the surface of lithium-nickel metal oxide particles, thereby combining into the bonding structure represented by Formula 1 or Formula 1-1 above.

[0058] The positive electrode active material can include nickel-cobalt-manganese (NCM) based lithium oxides. In this case, NCM-based lithium oxides with increased nickel content can be used.

[0059] Ni can be provided as a transition metal related to the output and capacity of lithium secondary batteries. Therefore, as described above, by using a high-content (high-Ni) composition in the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0060] However, with increasing Ni content, the long-term storage stability and cycle life stability of the cathode 110 or secondary battery may relatively decrease, and side reactions with the electrolyte may also increase. According to an exemplary embodiment, cycle life stability and capacity retention characteristics can be improved by increasing Mn, while electrical conductivity can be maintained by including Co.

[0061] The Ni content in NCM-based lithium oxides (e.g., the mole fraction of nickel based on the total molar amount of nickel, cobalt, and manganese) can be 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content can be 0.8-0.95, 0.82-0.95, 0.83-0.95, 0.84-0.95, 0.85-0.95, or 0.88-0.95.

[0062] In some embodiments, the positive electrode active material may include lithium cobalt oxide-based active material, lithium manganese oxide-based active material, lithium nickel oxide-based active material, or lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0063] In some embodiments, the positive electrode active material may include, for example, a lithium (Li)-rich layered oxide (LLO) / over-lithiated oxide (OLO)-based active material, a manganese (Mn)-rich active material, or a cobalt (Co)-less active material, which has a chemical structure or crystal structure represented by Formula 2 below. These materials may be used alone or in combination of two or more.

[0064] [Formula 2]

[0065] p[Li2MnO3]·(1-p)[Li q JO2]

[0066] In Formula 2, p and q may satisfy 0 < p < 1 and 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0067] Based on the total weight of the first positive electrode active material layer 114, the content of the positive electrode active material may be 40 wt% or more, 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0068] Based on the total weight of the first positive electrode active material layer 114, the content of the positive electrode active material may be 99 wt% or less, 95 wt% or less, 90 wt% or less, or 85 wt% or less.

[0069] Based on the total weight of the second positive electrode active material layer 116, the content of the positive electrode active material may be 40 wt% or more, 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0070] Based on the total weight of the second positive electrode active material layer 116, the content of the positive electrode active material may be 99 wt% or less, 95 wt% or less, 90 wt% or less, or 85 wt% or less.

[0071] The aforementioned positive electrode active materials can be mixed in a solvent to prepare a positive electrode slurry. The positive electrode slurry can be coated or deposited onto the first surface 112a and the second surface 112b of the positive electrode current collector 112, and then dried and rolled to prepare a first positive electrode active material layer 114 and a second positive electrode active material layer 116. Coating methods can include, for example, gravure coating, slot die coating, simultaneous multilayer die coating, embossing, blade coating, dip coating, rod coating, casting, etc.

[0072] The first positive electrode active material layer 114 and the second positive electrode active material layer 116 may each further include a binder, and optionally further include a thickener, etc.

[0073] Solvents may include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0074] Adhesives may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These adhesives can be used alone or in combination of two or more.

[0075] In one embodiment, a PVDF-based binder can be used as the positive electrode binder. In this case, the amount of binder used to form the first positive electrode active material layer 114 and the second positive electrode active material layer 116 can be reduced, and the amount of positive electrode active material can be relatively increased. Therefore, the output performance and capacity characteristics of the secondary battery can be improved.

[0076] The cathode slurry may also contain thickeners and / or dispersants. In one embodiment, the cathode slurry may also contain a thickener, such as carboxymethyl cellulose (CMC).

[0077] Figure 2 and Figure 3 These are schematic plan views and cross-sectional views illustrating a lithium secondary battery according to an exemplary embodiment. For example, Figure 3 It is along Figure 2 A cross-sectional view taken from the I-I' line.

[0078] In some embodiments, the diameter of the core 50 can be from 3 mm to 8 mm. Within this range, the electrodes can be adequately accommodated, thereby improving the capacity characteristics of the secondary battery, and the loading difference between the first positive electrode active material layer 114 and the second positive electrode active material layer 116 can be appropriately adjusted. Therefore, cycle life characteristics and operational reliability can be improved.

[0079] The electrode assembly 100 may include the aforementioned positive electrode 110, a negative electrode 120 disposed opposite to the positive electrode 110, and a diaphragm 130 disposed between the positive electrode 110 and the negative electrode 120.

[0080] In some implementations, the secondary battery may include a jelly roll structure, wherein the electrode assembly 100 is repeatedly wound around the core 50.

[0081] In one embodiment, the electrode assembly 100 can be placed on a core pin, repeatedly wound around the core pin, and then the core pin can be removed to form a jelly roll structure.

[0082] In one embodiment, the core 50 may represent a gap formed by removing the core pin. In one embodiment, the size and shape of the core 50 may be substantially the same as the size and shape of the core pin. In one embodiment, the diameter of the core 50 may be substantially the same as the diameter of the core pin.

[0083] In one implementation, the core pin may include metal and / or alloy.

[0084] In one embodiment, the negative electrode 120, the separator 130, and the positive electrode 110 can be stacked sequentially and repeatedly by a winding process.

[0085] In one embodiment, the negative electrode 120, the positive electrode 110, and the separator 130 may be stacked and wound such that the separator 130 is disposed between each negative electrode 120 and the positive electrode 110.

[0086] In one embodiment, depending on the winding process, a sequentially stacked structure of negative electrode 120, separator 130, positive electrode 110, separator 130, negative electrode 120, separator 130 and positive electrode 110 can be repeatedly formed on the core 50.

[0087] In an exemplary embodiment, the secondary battery can satisfy Equation 1 below.

[0088] [Equation 1]

[0089] Y = AX 2 - BX + C

[0090] In Equation 1, X represents the diameter of core 50, Y represents the load difference defined by Equation 2 below, where A is 0.0062 to 0.013, B is 0.1242 to 0.2622, and C is 0.943 to 1.9907.

[0091] [Equation 2]

[0092] Load difference (mg / cm) 2 = LW2 - LW1

[0093] In Equation 2, LW1 represents the loading amount (mg / cm³) of the first positive electrode active material layer 114. 2 LW2 represents the loading amount of the second positive electrode active material layer 116.

[0094] As used herein, the term "load capacity" can refer to the load per unit area (1 cm²). 2 The weight (mg) of ).

[0095] Figure 4 This is a graph illustrating Equation 1.

[0096] According to the implementation scheme that satisfies Equation 1, the (X, Y) coordinates representing the difference between the core diameter (X) and the load (Y) of the secondary battery can be located at... Figure 4 The region between the two quadratic curves shown.

[0097] exist Figure 4 In the diagram, the shaded region represents the area where the (X, Y) coordinates of some embodiments of the core 50 with a diameter (X) of 3 mm to 8 mm are located, but the location of the (X, Y) coordinates of embodiments of the present invention is not limited to the shaded region.

[0098] When the (X, Y) coordinates of the secondary battery satisfy Equation 1, the change in electrode capacity caused by the position on the positive electrode is minimized, thereby preventing the deposition of internal positive electrode material (e.g., lithium) and allowing the capacity of the positive electrode 110 to be sufficiently improved, which can maintain or improve the capacity retention rate.

[0099] For example, based on the diameter (X) of the core 50, within a certain range (e.g., Figure 4 The load difference (Y) is adjusted within the region between the two quadratic curves shown, thereby improving the capacity expression rate of the secondary battery according to the diameter (X) of the core 50, and improving the long-term cycle life characteristics and operational reliability.

[0100] In some implementations, the loading difference can be 0.3 mg / cm³.2 Up to 1.1 mg / cm 2 In one implementation, the loading difference can be 0.45 mg / cm³. 2 Up to 0.8 mg / cm 2 Within the aforementioned range, location-dependent differences in electrode capacity are mitigated, thereby preventing the deposition of internal positive electrode material (e.g., lithium) and allowing the capacity of the positive electrode 110 to be sufficiently enhanced, which can maintain or improve capacity retention.

[0101] In some embodiments, the loading (LW1) of the first positive electrode active material layer 114 can be 7.6 mg / cm³. 2 Up to 49.6 mg / cm 2 Within this range, the capacity characteristics of the positive electrode 110 can be enhanced, and operational reliability can also be improved.

[0102] In some embodiments, the loading (LW2) of the second positive electrode active material layer 116 can be 8 mg / cm³. 2 Up to 50 mg / cm 2 Within this range, the capacity characteristics of the positive electrode 110 can be enhanced, and operational reliability can also be improved.

[0103] In some embodiments, the overall density of the first positive electrode active material layer 114 and the second positive electrode active material layer 116 can be 3.2 g / cm³. 3 Up to 3.8 g / cm 3 Within this range, the density of the positive electrode 110 can be variably adjusted, while suppressing the aforementioned lithium precipitation and improving operational reliability.

[0104] "Overall density" can refer to the ratio of the total mass of the first positive electrode active material layer 114 and the second positive electrode active material layer 116 to the total volume of the first positive electrode active material layer 114 and the second positive electrode active material layer 116.

[0105] In some embodiments, the average loading amount (LW1) of the first positive electrode active material layer 114 and the loading amount (LW2) of the second positive electrode active material layer 116 can be 16 mg / cm³. 2 Up to 30 mg / cm 2 Within this range, the aforementioned lithium precipitation can be suppressed, and operational reliability can be improved, while the loading amounts (LW1, LW2) of the first positive electrode active material layer 114 and the second positive electrode active material layer 116 can be variably adjusted.

[0106] In some implementations, the difference between the CA ratio (CA as defined in Equation 3 below) of the core portion CR closest to the core 50 and the CA ratio of the end portion ER furthest from the core 50 can be 0% to 0.2%.

[0107] [Equation 3]

[0108] CA ratio (%) = (CC / CA) × 100

[0109] In Equation 3, CC represents the discharge capacity (mAh / g) of the positive electrode 110 of the secondary battery, and CA represents the discharge capacity (mAh / g) of the negative electrode 120 of the secondary battery.

[0110] Within the aforementioned range, the capacity expression of the electrode assembly 100, depending on its location, can be more uniform.

[0111] Figure 5 This is a schematic cross-sectional view showing the negative electrode according to an exemplary embodiment.

[0112] refer to Figure 5 The negative electrode 120 may include a negative electrode current collector 122 and a negative electrode active material layer 124 disposed on at least one surface of the negative electrode current collector 122. In one embodiment, the negative electrode active material layer 124 may be disposed on both surfaces of the negative electrode current collector 122.

[0113] For example, the negative electrode current collector 122 may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, etc. These can be used alone or in combination. In one embodiment, the negative electrode current collector 122 may have a thickness of 10 μm to 50 μm.

[0114] The negative electrode active material layer 124 may include a negative electrode active material. Materials capable of intercalating and deintercalating lithium ions can be used as negative electrode active materials. For example, negative electrode active materials may include crystalline carbon-based materials, such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers; lithium metal; lithium alloys; silicon-containing (Si) materials, tin-containing (Sn) materials, etc. These can be used alone or in combination.

[0115] Amorphous carbon can include hard carbon, soft carbon, coke, mesophase carbon microspheres (MCMB), mesophase pitch-based carbon fibers (MPCF), etc.

[0116] Crystalline carbon can include graphite-based carbon, such as natural graphite, artificial graphite, graphite coke, graphite MCMB, graphite MPCF, etc.

[0117] The lithium metal may include pure lithium metal and / or lithium metal with a protective layer formed thereon for suppressing dendrite growth and the like. In one embodiment, the lithium metal-containing layer deposited or coated on the negative electrode current collector 122 may be used as the negative electrode active material layer 124. In one embodiment, a lithium thin-film layer may be used as the negative electrode active material layer 124.

[0118] The elements constituting the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc. These may be used alone or in combination of two or more.

[0119] The silicon-containing material may provide enhanced capacity characteristics. The silicon-containing material may include Si, SiOx (0 < x < 2), metal-doped SiOx (0 < x < 2), silicon-carbon composite materials, etc.

[0120] The metal may include lithium and / or magnesium, and the metal-doped SiO x (0 < x < 2) may include metal silicate.

[0121] The negative electrode paste may be prepared by mixing the negative electrode active material in a solvent. The negative electrode paste may be coated or deposited on the negative electrode current collector 122, and then dried and roll-pressed to prepare the negative electrode active material layer 124. The coating process may be carried out using methods such as gravure coating, slot die coating, simultaneous multi-layer die coating, imprinting, knife coating, dip coating, bar coating, casting, etc. The negative electrode active material layer 124 may further include an adhesive, and optionally may also include a conductive material and / or a thickening agent.

[0122] The solvent in the negative electrode paste may include water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propanol, tert-butanol, etc. These may be used alone or in combination of two or more.

[0123] In some embodiments, the materials that can be used as adhesives, conductive materials, and thickening agents in the preparation of the positive electrode 110 above may be additionally used for the negative electrode.

[0124] In some embodiments, a styrene-butadiene rubber (SBR)-based adhesive, carboxymethyl cellulose (CMC), polyacrylic acid-based adhesive, or poly(3,4-ethylenedioxythiophene) (PEDOT)-based adhesive, etc. may be used as the negative electrode adhesive. These may be used alone or in combination of two or more.

[0125] The separator 130 may be configured to prevent an electrical short circuit between the positive electrode 110 and the negative electrode 120 and allow ion flow therethrough. For example, the thickness of the separator may be 10 μm to 20 μm.

[0126] In some embodiments, the diaphragm 130 may comprise a porous polymer membrane or a porous nonwoven fabric.

[0127] Porous polymer membranes may include polyolefin-based polymers, such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, or ethylene / methacrylate copolymers. These can be used alone or in combination of two or more.

[0128] Porous nonwoven fabrics may include glass fibers with high melting points. In some embodiments, porous nonwoven fabrics may include polyethylene terephthalate fibers, etc.

[0129] The diaphragm 130 may also include a ceramic-based material. For example, inorganic particles may be coated on or dispersed within the polymer membrane to improve heat resistance.

[0130] The diaphragm 130 may have a single-layer or multi-layer structure including the aforementioned polymer membrane and / or nonwoven fabric.

[0131] In some embodiments, the secondary battery may also include a housing 140 that accommodates the electrode assembly 100.

[0132] For example, electrode assembly 100 may be housed together with electrolyte within housing 140 to define a lithium secondary battery. In some exemplary embodiments, a non-aqueous electrolyte may be used.

[0133] Non-aqueous electrolytes may include lithium salts of the electrolyte and organic solvents, wherein the lithium salt can be derived from Li... + X - This indicates that the lithium salt (X) - ) can include F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N- (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - (CF3CF2SO2)2N - wait.

[0134] Organic solvents can include propylene carbonate (PC), ethylene carbonate (EC), butenyl carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), ethyl fluorocarbonate (FEA), ethyl difluorocarbonate (DFEA), ethyl trifluorocarbonate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethanol, isopropanol, dimethyl sulfoxide, acetonitrile, diethoxyethane, sulfolane, γ-butyrolactone, propylene sulfite, etc. These can be used alone or in combination of two or more.

[0135] Non-aqueous electrolytes may also contain additives. Additives may include, for example, cyclic carbonate compounds, fluorine-substituted carbonate compounds, sultone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, borate compounds, etc. These can be used alone or in combination of two or more.

[0136] Cyclic carbonate compounds can include vinylene carbonate (VC), ethylene ethylene carbonate (VEC), etc.

[0137] Fluorinated cyclic carbonate compounds can include fluoroethylene carbonate (FEC), etc.

[0138] Sulfolactone compounds may include 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, or 1,4-butanesulfonate lactone, etc.

[0139] Cyclic sulfate compounds may include 1,2-vinyl sulfate, 1,2-propenyl sulfate, etc.

[0140] Cyclic sulfite compounds can include ethylene sulfite, butene sulfite, etc.

[0141] Phosphate compounds can include lithium difluorobis(oxalato)phosphate, lithium difluorophosphate, etc.

[0142] Borate compounds can include lithium bis(oxalate) borate, etc.

[0143] In some embodiments, a solid electrolyte can be used instead of the non-aqueous electrolyte described above. In this case, the lithium secondary battery can be manufactured as an all-solid-state battery. In some embodiments, a solid electrolyte layer can be disposed between the positive electrode 110 and the negative electrode 110, instead of the separator 130 described above.

[0144] Solid electrolytes may include sulfide-based electrolytes. As non-limiting examples, sulfide-based electrolytes may include Li₂S-P₂S₅, Li₂S-P₂S₅-LiCl, Li₂S-P₂S₅-LiBr, Li₂S-P₂S₅-LiCl-LiBr, Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, and Li₂S-P₂S₅-Z. m S n (m and n are positive numbers, Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, M is P, Si, Ge, B, Al, Ga, or In), Li7-xPS6-xCl x (0≤x≤2), Li7-xPS6-xBr x (0≤x≤2), Li7-xPS6-xI x(0≤x≤2). These can be used individually or in combination of two or more.

[0145] In one embodiment, the solid electrolyte may further include oxide-based amorphous solid electrolytes, such as Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li2O-B2O3-ZnO, etc.

[0146] Electrode tabs (positive and negative) may extend from the positive current collector 112 and the negative current collector 122, respectively, and may extend to one side of the housing 140. The electrode tabs may be fused to one side of the housing 140 to form electrode leads (positive and negative leads) extending or exposed outside the housing 140.

[0147] In an exemplary embodiment, the housing 140 may have a cylindrical shape.

[0148] In an exemplary embodiment, the secondary battery can be configured as a cylindrical secondary battery. Therefore, the effect produced by the loading ratio of the aforementioned positive electrode 110 can be further improved.

[0149] In the following description, embodiments of the invention will be further described with reference to specific experimental examples. However, the following embodiments and comparative examples included in the experimental examples are for illustrative purposes only, and those skilled in the art will readily understand that various changes and modifications can be made within the scope and spirit of the invention. These changes and modifications are suitably included in the appended claims.

[0150] Example

[0151] Example A - Manufacturing of the positive electrode

[0152] NiSO4, CoSO4, and MnSO4 were added to distilled water (after dissolved oxygen was removed) in a molar ratio of 0.8:0.1:0.1 and mixed. A mixed solution was prepared by bubbling N2 into the solution for 24 hours. The mixed solution was then introduced into a reactor at 55°C, and a co-precipitation reaction was carried out using NaOH as a precipitant and NH3H2O ​​as a chelating agent for 36 hours to obtain Ni. 0.8 Co 0.1 Mn 0.1 (OH)₂ was used as a transition metal precursor. The transition metal precursor was dried at 80°C for 12 hours, and then dried again at 110°C for 12 hours.

[0153] Lithium hydroxide and a transition metal precursor were added to a dry high-speed mixer at a ratio of 1.05:1 and mixed uniformly for 5 minutes. The mixture was then placed in a calcination furnace under an oxygen atmosphere and heated to 950°C at a heating rate of 2°C / min, and maintained at 950°C for 12 hours. Oxygen was continuously supplied at a flow rate of 10 mL / min during heating and calcination. After calcination, the calcined product was allowed to cool naturally to room temperature, then pulverized and graded to obtain a LiNi composition. 0.8 Co 0.1 Mn 0.1 O2 positive electrode active material (median particle size (D50): 10 μm).

[0154] A positive electrode slurry is prepared by mixing positive electrode active material, carbon black as a conductive material, and PVDF as a binder in a mass ratio of 95:3:2. The positive electrode slurry is coated on both surfaces of an aluminum current collector, then dried and rolled to manufacture a positive electrode comprising a first positive electrode active material layer and a second positive electrode active material layer.

[0155] As shown in Table 1 below, the loading amounts of the first positive electrode active material layer and the second positive electrode active material layer, as well as the loading difference defined by Equation 2, were adjusted. Table 1 lists the results of Examples 1-17 and Comparative Examples 1-5.

[0156] Example B - Manufacturing of a Secondary Battery

[0157] A negative electrode slurry was prepared, comprising 93% by weight natural graphite as the negative electrode active material, 5% by weight flake graphite (KS6) as the conductive material, 1% by weight styrene-butadiene rubber (SBR) as the binder, and 1% by weight carboxymethyl cellulose (CMC) as the thickener. The negative electrode slurry was coated on both surfaces of a copper current collector, then dried and rolled to prepare the negative electrode.

[0158] The negative electrode, separator (polyethylene, thickness: 25 μm), and positive electrode are repeatedly stacked to form an electrode assembly. The electrode assembly is repeatedly wound around a core pin, and then the core pin is removed to form a wound structure. When this structure is wound, the first positive electrode active material layer is closer to the core pin than the second positive electrode active material layer.

[0159] The diameter of the core in this winding structure is the same as the diameter of the core pin.

[0160] Use metal rods with the diameters (core diameters) shown in Table 1 as core pins.

[0161] The wound structure is placed inside a cylindrical housing, and electrolyte is injected. Then, the cap is installed and clamped.

[0162] The electrolyte used here was prepared by adding 2.0 vol% fluoroethylene carbonate (FEC) to a 1M LiPF6 solution based on the total volume of the electrolyte. This LiPF6 solution was prepared using a mixed solvent of EC / EMC (3:7; volume ratio). After clamping, the structure was immersed for 3–24 hours, and then subjected to three charge-discharge cycles at 0.1C (charging conditions: CC-CV 0.1C 0.01V CUT-OFF, discharging conditions: CC 0.1C 1.5V CUT-OFF).

[0163] Example C - Measurement of CA ratio of core and end portions

[0164] The CA ratio of the secondary batteries of the above-described embodiments and comparative examples was measured at the core and end, respectively.

[0165] In a 25°C room, the secondary battery was repeatedly charged (CC-CV 0.1C 4.3V, 0.05C CUT-OFF) and discharged (CC 0.1C 3.0V CUT-OFF) three times, and the discharge capacity of the core and end of the positive electrode was measured.

[0166] In a 25°C room, the secondary battery was repeatedly charged (CC-CV 0.1C 0.01V, 0.01C CUT-OFF) and discharged (CC 0.1C 1.5V CUT-OFF) three times, and the discharge capacity of the core and end of the negative electrode was measured.

[0167] The CA ratios of the core and the end are calculated by substituting the discharge capacity values ​​into Equation 3.

[0168] Example D: Evaluation of the presence of lithium precipitate

[0169] The secondary batteries of the above embodiments and comparative examples were repeatedly charged (CC-CV 0.5C 4.3V 0.05C CUT-OFF) and discharged (CC 1.0C 2.5V CUT-OFF) 100 times in a room at 25°C. The secondary batteries were disassembled, and the lithium deposits in the electrode assembly were visually observed and evaluated as follows:

[0170] ○: Lithium precipitation was observed.

[0171] X: No lithium precipitation was observed.

[0172] Example E: Evaluation of Capacity Retention

[0173] In a room at 25°C, the secondary batteries of the above-described embodiments and comparative examples were repeatedly charged (CC-CV 0.5C 4.3V 0.05C CUT-OFF) and discharged (CC 1.0C 2.5V CUT-OFF) 100 times. Then, the discharge capacity of the 100th cycle was divided by the discharge capacity of the 1st cycle and multiplied by 100 to evaluate the capacity retention.

[0174] The measurement and evaluation results are shown in Table 2.

[0175] The loading amount of the first positive electrode active material layer (LW1), the loading amount of the second positive electrode active material layer (LW2), the loading amount difference defined by Equation 2, and the core diameter (core pin diameter) are shown in Table 1 below.

[0176] [Table 1]

[0177]

[0178] Table 2 below shows the CA ratio of the core and end portions, the difference in CA ratio between the core and end portions, the presence of lithium deposits, and capacity retention according to Equation 3.

[0179] [Table 2]

[0180]

[0181] Referring to Tables 1 and 2, in the embodiments that satisfy Equation 1, lithium precipitation is suppressed and capacity retention is improved compared to the comparative examples.

[0182] According to Equation 2, the difference in loading (Y) is 0.3 mg / cm³. 2 Up to 1.1 mg / cm 2 Examples 6 and 7, which are outside the scope of the other examples, have a relatively lower capacity retention rate compared to the other examples.

[0183] The loading (LW2) of the second positive electrode active material layer is 8 mg / cm³. 2 Up to 50 mg / cm 2 Examples 8 and 9, which are outside the scope of the other examples, have a relatively lower capacity retention rate compared to the other examples.

[0184] The loading (LW1) of the first positive electrode active material layer is 7.6 mg / cm³. 2 Up to 49.6 mg / cm 2 Examples 10 and 11, which are outside the scope of the other examples, have a relatively lower capacity retention rate compared to the other examples.

[0185] Examples 16 and 17, with core diameters outside the range of 3 mm to 8 mm, exhibited relatively lower capacity retention compared to other examples.

[0186] Example F: For 16 mg / cm 2 The average loading capacity is assessed based on variations in cathode density and average loading capacity.

[0187] The ratio of the total mass of the first positive electrode active material layer and the second positive electrode active material layer to the total volume of the first positive electrode active material and the second positive electrode active material is expressed as the positive electrode density.

[0188] The secondary battery was manufactured in the same manner as in Example 2, except that the positive electrode density and core diameter were adjusted as shown in Table 3 below, and the average value of LW1 and LW2 was adjusted to 16 mg / cm². 2 .

[0189] Adjust the core diameter using a metal rod with the diameters (core diameters) shown in Table 3. Calculate the average value by adding LW1 and LW2 and dividing the sum by 2.

[0190] In Table 3, the presence of lithium precipitate was evaluated in the same manner as described in Example D.

[0191] [Table 3]

[0192]

[0193] Example G: For 21.5 mg / cm 2 The average loading capacity is assessed based on variations in cathode density and average loading capacity.

[0194] The ratio of the total mass of the first positive electrode active material layer and the second positive electrode active material layer to the total volume of the first positive electrode active material layer and the second positive electrode active material layer is expressed as the positive electrode density.

[0195] The secondary battery was manufactured in the same manner as in Example 2, except that the positive electrode density and core diameter were adjusted as shown in Table 4 below, and the average value of LW1 and LW2 was adjusted to 21.5 mg / cm². 2 .

[0196] Adjust the core diameter using a metal rod with the diameters (core diameters) shown in Table 4. Calculate the average value by adding LW1 and LW2 and dividing the sum by 2.

[0197] In Table 4, the presence of lithium precipitate was evaluated in the same manner as described in Example D.

[0198] [Table 4]

[0199]

[0200] Example H: For 30 mg / cm 2The average loading capacity is assessed based on variations in cathode density and average loading capacity.

[0201] The ratio of the total mass of the first positive electrode active material layer and the second positive electrode active material layer to the total volume of the first positive electrode active material layer and the second positive electrode active material layer is expressed as the positive electrode density.

[0202] The secondary battery was manufactured in the same manner as in Example 2, except that the positive electrode density and core diameter were adjusted as shown in Table 5 below, and the average value of LW1 and LW2 was adjusted to 30 mg / cm². 2 .

[0203] Adjust the core diameter using a metal rod with the diameters (core diameters) shown in Table 5. Calculate the average value by adding LW1 and LW2 and dividing the sum by 2.

[0204] In Table 5, the presence of lithium precipitate was evaluated in the same manner as described in Example D.

[0205] [Table 5]

[0206]

[0207] Referring to Tables 3 to 5, in the secondary battery according to the embodiment, even when the positive electrode density is 3.2 g / cm³, 3 Up to 3.8 g / cm 3 When the range is variably adjusted, lithium will not precipitate as long as Equation 1 is satisfied, thereby improving long-term cycle life characteristics.

[0208] In the secondary battery according to the embodiment, even at 16 mg / cm³ 2 Up to 30 mg / cm 2 The average loading of the first positive electrode active material layer and the second positive electrode active material can be variably adjusted within a certain range. As long as Equation 1 is satisfied, lithium will not precipitate, thereby improving long-term cycle life characteristics.

Claims

1. A secondary battery comprising an electrode assembly, the electrode assembly including a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separator disposed between the positive electrode and the negative electrode, the electrode assembly being wound around a core; The positive electrode includes: A positive current collector, comprising a first surface and a second surface opposite to each other; A first positive electrode active material layer disposed on the first surface; and The second positive electrode active material layer is disposed on the second surface. The secondary battery satisfies Equation 1: [Equation 1] Y = AX 2 - BX + C; Where X represents the diameter of the core, Y represents the load difference defined by Equation 2, A is 0.0062 to 0.013, B is 0.1242 to 0.2622, and C is 0.943 to 1.9907; [Equation 2]: Load difference (mg / cm) 2 = LW2 - LW1 Where LW1 represents the loading amount of the first positive electrode active material layer, in mg / cm³. 2 LW2 represents the loading amount of the second positive electrode active material layer, in mg / cm³. 2 .

2. The secondary battery according to claim 1, wherein, The first positive electrode active material layer is closer to the core than the second positive electrode active material layer.

3. The secondary battery according to claim 1, wherein, In Equation 1, X ranges from 3 mm to 8 mm.

4. The secondary battery according to claim 1, wherein, The difference in loading was 0.3 mg / cm³. 2 Up to 1.1 mg / cm 2 .

5. The secondary battery according to claim 1, wherein, The difference in loading was 0.45 mg / cm³. 2 Up to 0.8 mg / cm 2 .

6. The secondary battery according to claim 1, wherein, In Equation 2, LW1 is 7.6 mg / cm³. 2 Up to 49.6 mg / cm 2 .

7. The secondary battery according to claim 1, wherein, LW2 in Equation 2 is 8 mg / cm³ 2 Up to 50 mg / cm 2 .

8. The secondary battery according to claim 1, wherein, The overall density of the first positive electrode active material layer and the second positive electrode active material layer is 3.2 g / cm³. 3 Up to 3.8 g / cm 3 .

9. The secondary battery according to claim 1, wherein, The average value of LW1 and LW2 in Equation 2 is 16 mg / cm³. 2 Up to 30 mg / cm 2 .

10. The secondary battery of claim 1, further comprising a housing accommodating the electrode assembly.

11. The secondary battery according to claim 10, wherein the outer casing has a cylindrical shape.

12. The secondary battery of claim 1, wherein the electrode assembly comprises a jelly roll structure repeatedly wound around the core.

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