Positive electrode for lithium secondary battery and lithium secondary battery including the same

Abstract

To provide a positive electrode for a lithium secondary battery with improved life characteristics, and a lithium secondary battery including the same.SOLUTION: A positive electrode for a lithium secondary battery according to an embodiment of the present disclosure includes: a positive electrode collector; a first positive electrode active material layer that is arranged on at least one surface of the positive electrode collector, and includes a first positive electrode active material including boron; and a second positive electrode active material layer that is arranged on the first positive electrode active material layer, and includes a second positive electrode active material different from the first positive electrode active material. The Raman peak intensity ratio of the first positive electrode active material layer is smaller than the Raman peak intensity ratio of the second positive electrode active material layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The disclosure of the present application relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the same.

Background Art

[0002] A secondary battery is a battery that can be repeatedly charged and discharged, and with the development of the information communication and display industries, it is widely applied as a power source for portable electronic communication devices such as camcorders, mobile phones, and notebook computers. Recently, battery packs including secondary batteries have also been developed and applied as power sources for environmentally friendly vehicles such as electric vehicles.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, nickel-metal hydride batteries, etc. Among them, lithium secondary batteries are actively developed and applied because of their high operating voltage and energy density per unit weight, and their advantages in charging speed and weight reduction.

[0004] Recently, while the application targets of lithium secondary batteries are expanding, the development of lithium secondary batteries with higher capacities and outputs is underway. For example, the capacity characteristics and life characteristics of lithium secondary batteries may deteriorate depending on the positive electrode structure, positive electrode active material, and conductive material contained in the positive electrode of the lithium secondary battery.

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to one aspect of the present disclosure, a positive electrode for a lithium secondary battery with improved life characteristics can be provided.

[0006] According to one aspect of the present disclosure, a lithium secondary battery with improved life characteristics can be provided.

Means for Solving the Problems

[0007] The positive electrode for a lithium secondary battery according to an exemplary embodiment of the present disclosure includes a positive electrode current collector, a first positive electrode active material layer disposed on at least one surface of the positive electrode current collector and containing a first positive electrode active material, and a second positive electrode active material layer disposed on the first positive electrode active material layer and containing a second positive electrode active material different from the first positive electrode active material. The first positive electrode active material contains boron, and the first Raman peak intensity ratio defined by the following formula 1 is smaller than the second Raman peak intensity ratio defined by the following formula 2.

[0008] [Formula 1] First Raman peak intensity ratio = ID1 / IG1

[0009] [Formula 2] Second Raman peak intensity ratio = ID2 / IG2

[0010] In Formula 1 and Formula 2, ID1 is the maximum peak intensity in the wavenumber range of 1300 cm -1 ~1400 cm -1 in the Raman spectrum of the first positive electrode active material layer, IG1 is the maximum peak intensity in the wavenumber range of 1550 cm -1 ~1650 cm -1 in the Raman spectrum of the first positive electrode active material layer, ID2 is the maximum peak intensity in the wavenumber range of 1300 cm -1 ~1400 cm -1 in the Raman spectrum of the second positive electrode active material layer, and IG2 is the maximum peak intensity in the wavenumber range of 1550 cm -1 ~1650 cm -1 in the Raman spectrum of the second positive electrode active material layer.

[0011] In some embodiments, the first positive electrode active material may further contain at least one of titanium, aluminum, barium, cobalt, and zirconium.

[0012] In some embodiments, the second positive electrode active material may not contain boron.

[0013] In some embodiments, the first Raman peak intensity ratio may be 0.5 to 1.1.

[0014] In some embodiments, the second Raman peak intensity ratio may be 1.0 to 1.2.

[0015] In some embodiments, the first positive electrode active material layer and the second positive electrode active material layer may each further include a dot-shaped conductive material or a linear conductive material.

[0016] In some embodiments, the first positive electrode active material layer may include the dot-shaped conductive material, and the second positive electrode active material layer may include the linear conductive material.

[0017] In some embodiments, the dot-shaped conductive material may include at least one selected from the group consisting of graphite, carbon black, graphene, tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0018] In some embodiments, the linear conductive material may include carbon nanotubes.

[0019] In some embodiments, the boron content may be 0.5 wt% to 3 wt% based on the weight of the first positive electrode active material.

[0020] The lithium secondary battery according to an exemplary embodiment of the present disclosure includes the positive electrode for a lithium secondary battery described above and a negative electrode facing the positive electrode.

Advantages of the Invention

[0021] According to an embodiment of the present disclosure, the side reaction between the positive electrode active material and the electrolyte can be reduced, and the electrical conductivity of the positive electrode can be improved. Thereby, the life characteristics at high temperature can be improved.

[0022] According to one embodiment of the present disclosure, the high amorphousness of the second positive electrode active material layer improves the strength and stability of the positive electrode, and the crystallinity of the first positive electrode active material layer can reduce the resistance at high temperatures.

[0023] The positive electrode for a lithium secondary battery and the lithium secondary battery including the same according to the present disclosure can be widely applied in green technology fields such as electric vehicles, battery charging stations, and other solar power generation and wind power generation that use batteries. The positive electrode for a lithium secondary battery and the lithium secondary battery including the same according to the present disclosure can be used in environmentally friendly (eco-friendly) electric vehicles (Electric Vehicle), hybrid vehicles, etc. to suppress air pollution and greenhouse gas emissions and prevent climate change.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0025] Embodiments of the present disclosure provide a positive electrode for a lithium secondary battery (hereinafter, may be abbreviated as "positive electrode"). Further, a lithium secondary battery including the positive electrode (hereinafter, may be abbreviated as "secondary battery") is provided.

[0026] Hereinafter, embodiments of the present disclosure will be described more specifically. However, these embodiments are merely illustrative of the present disclosure and do not limit the present disclosure.

[0027] FIG. 1 is a schematic cross-sectional view showing a positive electrode for a lithium secondary battery according to an exemplary embodiment.

[0028] Referring to FIG. 1, the positive electrode 100 can include a positive electrode current collector 105, a first positive electrode active material layer 110, and a second positive electrode active material layer 120.

[0029] The positive electrode current collector 105 can include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector 105 can also include carbon, nickel, titanium, aluminum or stainless steel surface-treated with silver. For example, the thickness of the positive electrode current collector 105 may be 10 μm to 50 μm.

[0030] The first positive electrode active material layer 110 can be disposed on at least one surface of the positive electrode current collector 105.

[0031] The first positive electrode active material layer 110 can include a first positive electrode active material containing boron (B). By including boron in the first positive electrode active material adjacent to the positive electrode current collector 105 relatively, the side reaction between the first positive electrode active material and the electrolyte can be reduced, and the electrical conductivity of the positive electrode can be improved. Thereby, the resistance at high temperature can be reduced.

[0032] The boron may be coated on the surface portion of the first positive electrode active material or doped into the interior of the first positive electrode active material.

[0033] As used herein, the term "coating" can include a structure disposed on the surface portion of the first positive electrode active material and a structure partially doped into the interior of the first positive electrode active material.

[0034] In some embodiments, the first positive electrode active material can further include at least one of titanium (Ti), aluminum (Al), barium (Ba), cobalt (Co), and zirconium (Zr). Thereby, the electrical conductivity can be further improved and the side reaction can be suppressed. The element may be coated on the surface portion of the first positive electrode active material or doped into the interior of the first positive electrode active material.

[0035] In some embodiments, the boron content may be 0.5 wt% to 3 wt% based on the weight of the first positive electrode active material. Within this range, the life characteristics can be improved while maintaining the output characteristics of the first positive electrode active material.

[0036] According to one embodiment, the first positive electrode active material layer 110 can be arranged to directly contact the positive electrode current collector 105.

[0037] The content of the first positive electrode active material with respect to the total weight of the first positive electrode active material layer 110 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.

[0038] The content of the first positive electrode active material with respect to the total weight of the first positive electrode active material layer 110 may be 99 wt% or less, 95 wt% or less, 90 wt% or less, or 85 wt% or less.

[0039] In one embodiment, the positive electrode active material contained in the first positive electrode active material layer 110 may be substantially composed of the first positive electrode active material.

[0040] In an exemplary embodiment, a second positive electrode active material layer 120 can be arranged on the first positive electrode active material layer 110.

[0041] The second positive electrode active material layer 120 can contain a second positive electrode active material different from the first positive electrode active material.

[0042] In some embodiments, the second positive electrode active material may not contain boron. Thereby, it is possible to prevent a decrease in capacitance in the second positive electrode active material layer 110 which is relatively separated from the positive electrode current collector 105.

[0043] According to one embodiment, the second positive electrode active material layer 120 can be arranged to directly contact the first positive electrode active material layer 110.

[0044] The content of the second positive electrode active material with respect to the total weight of the second positive electrode active material layer 120 may be 40% by weight or more, 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more.

[0045] The content of the second positive electrode active material with respect to the total weight of the second positive electrode active material layer 120 may be 99% by weight or less, 95% by weight or less, 90% by weight or less, or 85% by weight or less.

[0046] In one embodiment, the positive electrode active material contained in the second positive electrode active material layer 120 may be substantially composed of the second positive electrode active material.

[0047] According to an exemplary embodiment, the first positive electrode active material and the second positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0048] In some embodiments, the first positive electrode active material and the second positive electrode active material, or the lithium-nickel metal oxide, may include a layered structure or a crystal structure represented by the following Chemical Formula 1.

[0049] [Chemical Formula 1] Li x Ni a M b O 2+z

[0050] In Chemical Formula 1, 0.9 ≦ x ≦ 1.2, 0.6 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.4, and -0.5 ≦ z ≦ 0.1 may be satisfied. As described above, M may include Co, Mn, and / or Al.

[0051] The chemical structure represented by Chemical Formula 1 shows the bonding relationships within the layered or crystal structure of the first positive electrode active material and the second positive electrode active material, and does not exclude other additional elements. For example, M includes Co and / or Mn, and Co and / or Mn can be provided as the main active elements of the first positive electrode active material and the second positive electrode active material together with Ni. Chemical Formula 1 is provided to represent the bonding relationships of the main active elements and should be understood as a formula that includes the introduction and substitution of additional elements.

[0052] In one embodiment, in addition to the main active elements, the first positive electrode active material and the second positive electrode active material, or the layered structure / crystal structure may further include auxiliary elements for improving chemical stability. The auxiliary elements can be incorporated together within the layered structure / crystal structure to form bonds. In this case as well, it should be understood that they are included within the scope of the chemical structure represented by Chemical Formula 1.

[0053] The auxiliary elements can include, for example, at least one selected from the group consisting of 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, and Zr. The auxiliary elements can also act as auxiliary active elements that contribute to the capacity / output activity of the first positive electrode active material and the second positive electrode active material together with Co or Mn, such as Al.

[0054] For example, the first positive electrode active material and the second positive electrode active material, or the lithium-nickel metal oxide can include a layered structure or crystal structure represented by the following Chemical Formula 1-1.

[0055] [Chemical Formula 1-1] Li x Ni a M1 b1 M2 b2 O 2+z

[0056] In Chemical Formula 1-1, M1 can include Co, Mn, and / or Al, and M2 can include the aforementioned auxiliary elements. In Chemical Formula 1-1, 0.9 ≦ x ≦ 1.2, 0.6 ≦ a ≦ 0.99, 0.01 ≦ b1 + b2 ≦ 0.4, and -0.5 ≦ z ≦ 0.1 may be satisfied.

[0057] In addition to the boron described above, the first cathode active material and the second cathode active material can further include a coating element or a doping element. For example, an element substantially the same as or similar to the aforementioned auxiliary element can be used as the coating element or the doping element. For example, the aforementioned elements can be used alone or in combination of two or more as the coating element or the doping element.

[0058] The coating element or the doping element may be present on the surface of the lithium-nickel metal oxide particles, or may penetrate from the surface of the lithium-nickel metal oxide particles and be included in the bonding structure represented by Chemical Formula 1 or Chemical Formula 1-1 above.

[0059] The first cathode active material and the second cathode active material can include a nickel-cobalt-manganese (NCM) based lithium oxide. In this case, an NCM based lithium oxide with an increased nickel content can be used.

[0060] Ni can be provided as a transition metal related to the output and capacity of the lithium secondary battery. Thus, by adopting the composition with a high content (High-Ni) as described above for the first cathode active material and the second cathode active material, a high-capacity cathode and a high-capacity lithium secondary battery can be provided.

[0061] However, as the Ni content increases, the long-term storage stability and life stability of the cathode or the secondary battery may relatively decrease, and the side reaction with the electrolyte may also increase. In contrast, according to an exemplary embodiment, by including Co, the electrical conductivity can be maintained, and the life stability and capacity retention characteristics can be improved by Mn.

[0062] The content of Ni in the NCM-based lithium oxide (for example, the molar fraction of Ni in the total number of moles of nickel, cobalt, and manganese) may be 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0063] In some embodiments, the first cathode active material and the second cathode active material may each contain a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate-based (LFP) active material (for example, LiFePO4).

[0064] In some embodiments, the first cathode active material and the second cathode active material may contain, for example, an LLO (Li rich layered oxide) / OLO (Over Lithiated Oxide)-based active material, an Mn-rich-based active material, a Co-less-based active material, etc. having a chemical structure or crystal structure represented by Chemical Formula 2. These can be used alone or in combination of two or more.

[0065] [Chemical Formula 2] p[Li2MnO3]·(1-p)[Li q JO2]

[0066] In Chemical Formula 2, 0 < p < 1 and 0.9 ≤ q ≤ 1.2, and J can contain at least one element of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0067] In an exemplary embodiment, the first Raman peak intensity ratio defined by the following Formula 1 may be smaller than the second Raman peak intensity ratio defined by the following Formula 2.

[0068] [Formula 1] First Raman peak intensity ratio = ID1 / IG1

[0069] [Formula 2] Second Raman peak intensity ratio = ID2 / IG2

[0070] In Formula 1, ID1 is the maximum peak intensity in the wavenumber range of 1300 cm -1 ~1400 cm -1 (for example, the D band of the Raman spectrum) in the Raman spectrum of the first positive electrode active material layer 110. IG1 is the maximum peak intensity in the wavenumber range of 1550 cm -1 ~1650 cm -1 (for example, the G band of the Raman spectrum) in the Raman spectrum of the first positive electrode active material layer 110.

[0071] In Formula 2, ID2 is the maximum peak intensity in the wavenumber range of 1300 cm -1 ~1400 cm -1 in the Raman spectrum of the second positive electrode active material layer 120, and IG2 is the maximum peak intensity in the wavenumber range of 1550 cm -1 ~1650 cm -1 in the Raman spectrum of the second positive electrode active material layer 120.

[0072] For example, the maximum peak intensity can represent the maximum peak height in a specific wavenumber range.

[0073] For example, the first and second Raman peak intensity ratios can indicate the degree of amorphousness. For example, the higher the first and second Raman peak intensity ratios, the higher the amorphousness of the first and second positive electrode active material layers 110, 120 can be.

[0074] Since the first Raman peak intensity ratio of the first positive electrode active material layer 110 is smaller than the second Raman peak intensity ratio of the second positive electrode active material layer 120, the high amorphousness of the second positive electrode active material layer 120 improves the strength and stability of the positive electrode 100, and the crystallinity of the first positive electrode active material layer 110 can reduce the resistance at high temperatures.

[0075] In some embodiments, the first Raman peak intensity ratio may be 0.5 to 1.1. In this range, the life characteristics can be further improved.

[0076] In some embodiments, the second Raman peak intensity ratio may be 1.0 to 1.2. In this range, the resistance at high temperatures can be further reduced.

[0077] The above-mentioned first Raman peak intensity ratio can be changed by comprehensively adjusting factors such as the type of conductive material contained in the first positive electrode active material layer 110 and the content of the conductive material in the total weight of the first positive electrode active material layer 110.

[0078] The above-mentioned second Raman peak intensity ratio can be changed by comprehensively adjusting factors such as the type of conductive material contained in the second positive electrode active material layer 120, the content of the conductive material in the total weight of the second positive electrode active material layer 120, and / or the average particle diameter (D50) of the second positive electrode active material.

[0079] In some embodiments, the first positive electrode active material layer 110 and the second positive electrode active material layer 120 can each further include a dot-shaped conductive material or a linear conductive material. Thereby, the electrical conductivity of the positive electrode 100 can be further improved.

[0080] As used herein, the term "dot-shaped conductive material" can mean a conductive material having an aspect ratio of 0.5 to 1.5. For example, the dot-shaped conductive material can include substantially spherical or elliptical shapes. The aspect ratio can mean the length of the dot-shaped conductive material with respect to its diameter.

[0081] As used herein, the term "linear conductive material" can mean a conductive material having an aspect ratio of 2 to 20. The aspect ratio can mean the length of the linear conductive material with respect to its diameter.

[0082] In some embodiments, the dot-shaped conductive material may include at least one selected from the group consisting of graphite, carbon black, graphene, tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0083] In some embodiments, the linear conductive material may include carbon nanotubes (CNTs). Thereby, the electrical conductivity, crystallinity, and stability of the positive electrode 100 can be improved.

[0084] For example, the linear conductive material may include at least one selected from the group consisting of single-walled CNTs (SWCNTs), double-walled CNTs (DWCNTs), multi-walled CNTs (MWCNTs), and rope CNTs.

[0085] In some embodiments, the length of the linear conductive material may be 10 μm to 55 μm. Within this range, while improving the electron mobility of the positive electrode 100, the distance between particles and the volume of the positive electrode 100 can be appropriately maintained.

[0086] According to one embodiment, the first positive electrode active material layer 110 may include a dot-shaped conductive material, and the second positive electrode active material layer 120 may include a linear conductive material. Thereby, the stability of the positive electrode can be improved while improving the electrical conductivity.

[0087] In some embodiments, the total content of the dot-shaped conductive material and the linear conductive material included in the first positive electrode active material layer 110 may be 1 wt% to 5 wt% based on the total weight of the first positive electrode active material layer 110. Within this range, the energy density and life characteristics of the positive electrode 100 can be improved.

[0088] In some embodiments, the total content of the dot-shaped conductive material and the linear conductive material contained in the second positive electrode active material layer 120 may be 1 wt% to 5 wt% based on the total weight of the second positive electrode active material layer 110. Within this range, the energy density and life characteristics of the positive electrode 100 can be improved.

[0089] FIG. 2 and FIG. 3 are a schematic plan view and a cross-sectional view showing a lithium secondary battery according to an exemplary embodiment, respectively. For example, FIG. 3 is a cross-sectional view taken along the thickness direction of "I-I'" in FIG. 2.

[0090] Referring to FIGS. 2 and 3, the lithium secondary battery may include the positive electrode 100 described above and a negative electrode 130 facing the positive electrode 100.

[0091] The first positive electrode active material layer 110 can be disposed on at least one surface of the positive electrode current collector 105, and the second positive electrode active material layer 120 can be disposed on the first positive electrode active material layer 110.

[0092] The first positive electrode active material described above can be mixed in a solvent to produce a first positive electrode slurry. After coating / vapor-depositing the first positive electrode slurry on at least one surface of the positive electrode current collector 105, it can be dried and rolled to produce the first positive electrode active material layer 110. The coating can include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc.

[0093] The second positive electrode active material described above can be mixed in a solvent to produce a second positive electrode slurry. After coating / vapor-depositing the second positive electrode slurry on the first positive electrode active material layer 110, it can be dried and rolled to produce the second positive electrode active material layer 120. The coating can be performed using a method substantially the same as the above-described coating method for the first positive electrode active material layer 110.

[0094] The first and second positive electrode active material layers 110 and 120 may each further contain a binder, and may selectively further contain a thickener or the like.

[0095] As the solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. can be used.

[0096] The binder may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethylmethacrylate, acrylonitrile-butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These can be used alone or in combination of two or more.

[0097] In one embodiment, a PVDF-based binder can be used as the positive electrode binder. In this case, the amount of the binder for forming the positive electrode active material layers 110 and 120 can be reduced, and the amount of the positive electrode active material can be relatively increased. Thereby, the output characteristics and capacity characteristics of the secondary battery can be improved.

[0098] The first and second positive electrode slurries may further contain a thickener and / or a dispersant or the like. In one embodiment, the first positive electrode slurry and / or the second positive electrode slurry may further contain a thickener such as carboxymethyl cellulose (CMC).

[0099] The negative electrode 130 can include a negative electrode current collector 135 and a negative electrode active material layer 140 formed on at least one surface of the negative electrode current collector 135.

[0100] For example, the negative electrode current collector 135 can include a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, and the like. These can be used alone or in combination of two or more. For example, the thickness of the negative electrode current collector 135 may be 10 μm to 50 μm.

[0101] The negative electrode active material layer 140 can include a negative electrode active material. As the negative electrode active material, a material capable of adsorbing and desorbing lithium ions can be used. For example, the negative electrode active material can be a carbon-based material such as crystalline carbon, amorphous carbon, carbon composite, carbon fiber; lithium metal; lithium alloy; silicon (Si)-containing substance or tin (Sn)-containing substance, etc. These can be used alone or in combination of two or more.

[0102] The amorphous carbon can include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), and the like.

[0103] The crystalline carbon can include graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like.

[0104] The lithium metal can include pure lithium metal and / or lithium metal with a protective layer formed for dendrite growth suppression. In one embodiment, a lithium metal-containing layer vapor-deposited or coated on the negative electrode current collector 135 can be used as the negative electrode active material layer 140. In one embodiment, a lithium thin film layer can also be used as the negative electrode active material layer 140.

[0105] Examples of the elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc. These can be used alone or in combination of two or more.

[0106] The silicon-containing substance can provide higher capacity characteristics. The silicon-containing substance can be Si, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), and can include silicon-carbon composites, etc.

[0107] The metal can include lithium and / or magnesium, and metal-doped SiO x (0 < x < 2) can include metal silicates.

[0108] The negative electrode active material can be mixed in a solvent to produce a negative electrode slurry. After coating / vapor depositing the negative electrode slurry on the negative electrode current collector 135, it can be dried and rolled to produce a negative electrode active material layer 140. The coating can include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc. The negative electrode active material layer 140 can further include a binder, and can selectively further include a conductive material, a thickener, etc.

[0109] Examples of the solvent contained in the negative electrode slurry can include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc. These can be used alone or in combination of two or more.

[0110] As the binder, conductive material, and thickener, the aforementioned substances that can be used during the manufacture of the positive electrode 100 can be used.

[0111] In some embodiments, as the negative electrode binder, a styrene-butadiene-rubber (SBR) based binder, carboxymethyl cellulose (CMC), a polyacrylic acid based binder, a poly(3,4-ethylenedioxythiophene) (PEDOT) based binder, etc. can be used. These can be used alone or in combination of two or more.

[0112] In an exemplary embodiment, a separator 150 can be interposed between the positive electrode 100 and the negative electrode 130. The separator 150 can be configured to prevent an electrical short circuit between the positive electrode 100 and the negative electrode 130 and allow the flow of ions to occur. For example, the thickness of the separator may be 10 μm to 20 μm.

[0113] For example, the separator 150 can include a porous polymer film or a porous nonwoven fabric.

[0114] The porous polymer film can include polyolefin-based polymers such as an ethylene polymer, a propylene polymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc. These can be used alone or in combination of two or more.

[0115] The porous nonwoven fabric can include high melting point glass fibers, polyethylene terephthalate fibers, etc.

[0116] The separation membrane 150 can also contain a ceramic-based material. For example, inorganic particles can be coated on the polymer film or dispersed in the polymer film to improve heat resistance.

[0117] The separation membrane 150 can have a single-layer or multi-layer structure including the above-described polymer film and / or nonwoven fabric.

[0118] According to an exemplary embodiment, an electrode cell is defined by the positive electrode 100, the negative electrode 130, and the separation membrane 150, and a plurality of electrode cells can be stacked to form, for example, a jelly roll type electrode assembly 160. For example, the electrode assembly 160 can be formed by winding, stacking, Z-folding, stack-folding, etc. of the separation membrane 150.

[0119] A lithium secondary battery can be defined by housing the electrode assembly 160 together with an electrolyte in a case 170. According to an exemplary embodiment, a non-aqueous electrolyte can be used as the electrolyte.

[0120] The non-aqueous electrolyte can contain a lithium salt as an electrolyte and an organic solvent. For example, the lithium salt can be represented by Li + X - . For example, as the anion (X - ) of the lithium salt, 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 - etc. can be mentioned.

[0121] Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl 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), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), and 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, propylene sulfite, etc. These can be used alone or in combination of two or more.

[0122] The non-aqueous electrolyte can further contain an additive. The additive can include, for example, cyclic carbonate compounds, fluorine-substituted carbonate compounds, sultone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, borate compounds, and the like. These can be used alone or in combination of two or more.

[0123] The cyclic carbonate compounds can include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and the like.

[0124] The fluorine-substituted cyclic carbonate compounds can include fluoroehtylene carbonate (FEC), and the like.

[0125] The sultone compounds can include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, and the like.

[0126] The cyclic sulfate compounds can include 1,2-ethylene sulfate, 1,2-propylene sulfate, and the like.

[0127] The cyclic sulfite compounds can include ethylene sulfite, butylene sulfite, and the like.

[0128] The phosphate compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.

[0129] The borate compound may include lithium bis(oxalate)borate, etc.

[0130] In some embodiments, a solid electrolyte can also be used instead of the aforementioned non-aqueous electrolyte. In this case, the lithium secondary battery can be manufactured in the form of an all-solid-state battery. Also, a solid electrolyte layer may be disposed between the positive electrode 100 and the negative electrode 130 instead of the aforementioned separator 150.

[0131] The solid electrolyte may include a sulfide-based electrolyte. As non-limiting examples, the sulfide-based electrolyte includes 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, Li2S-P2S5-Z m S n (m, n are positive numbers, and Z is Ge, Zn, or Ga.), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p, q are positive numbers, and 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 xIt can include, for example, (0≤x≤2). These can be used alone or in combination of two or more.

[0132] In one embodiment, the solid electrolyte can also include, for example, oxide-based amorphous solid electrolytes such as Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li2O-B2O3-ZnO.

[0133] As shown in FIGS. 2 and 3, electrode tabs (a positive electrode tab and a negative electrode tab) can protrude from the positive electrode current collector 105 and the negative electrode current collector 135 belonging to each electrode cell, respectively, and extend to one side of the case 170. The electrode tabs can be fused together with the one side of the case 170 to form electrode leads (a positive electrode lead 107 and a negative electrode lead 137) extending or exposed outside the case 170.

[0134] The lithium secondary battery can be manufactured, for example, in a cylindrical shape, a square shape, a pouch type, or a coin type using a can.

[0135] Hereinafter, specific examples are presented to assist in understanding the present invention. However, these examples are merely illustrative of the present invention and do not limit the appended claims. It is obvious to those skilled in the art that various changes and modifications can be made within the scope of the present invention and the scope of the technical idea, and it is natural that these modifications and changes belong to the appended claims.

[0136] Example 1 (1) Manufacture of the positive electrode 1) Manufacture of the first positive electrode active material layer NiSO4, CoSO4, and MnSO4 were added and mixed in a molar ratio of 0.88:0.09:0.03 to distilled water that had been bubbled with N2 for 24 hours to remove dissolved oxygen inside to produce a mixed solution. The mixed solution was introduced into a reactor at 55°C, and a coprecipitation reaction was carried out for 36 hours using NaOH and NH3H2O as a precipitating agent and a chelating agent, respectively, to obtain Ni as a transition metal precursor 0.88 Co0.09 Mn 0.03 (OH)2 was obtained. The transition metal precursor was dried at 80°C for 12 hours and then re-dried at 110°C for 12 hours.

[0137] Lithium hydroxide and the transition metal precursor were added to a dry high-speed mixer in a ratio of 1.05:1 and mixed uniformly for 5 minutes. The mixture was placed in a calcination furnace in an oxygen atmosphere, heated to 950°C at a heating rate of 2°C / min, and maintained at 950°C for 12 hours. During heating and calcination, oxygen was continuously passed through at a flow rate of 10 mL / min. After calcination, the mixture was naturally cooled to room temperature, crushed, and classified to obtain a product with a composition of LiNi 0.88 Co 0.09 Mn 0.03 A spare positive electrode active material of O2 was obtained (average particle size (D50): 10 μm).

[0138] The preliminary positive electrode active material was mixed with an aqueous solution of boron (B) as a coating / doping solution, and the mixture was fired at 200° C. to prepare a first positive electrode active material containing boron. The content of boron was 1.5 wt % based on the total weight of the first positive electrode active material.

[0139] The first positive electrode active material, carbon black as a dot-like conductive material, and PVDF as a binder were mixed in a mass ratio of 95:3:2 to prepare a first positive electrode slurry. The first positive electrode slurry was coated on an aluminum current collector, and then dried and rolled to form a first positive electrode active material layer.

[0140] The carbon black has an average particle size (D50) of 30 nm and a specific surface area of 254 m 2 / g.

[0141] 2) Preparation of the second positive electrode active material layer The boron-free preliminary positive electrode active material was used as a second positive electrode active material. The second positive electrode active material, carbon nanotubes (CNT) as a linear conductive material, and PVDF as a binder were mixed at a mass ratio of 95:3:2 respectively to produce a second positive electrode slurry. After coating the second positive electrode slurry on the first positive electrode active material layer, it was dried and rolled to form a second positive electrode active material layer. A positive electrode including an aluminum current collector, a first positive electrode active material layer, and a second positive electrode active material layer was formed. The length of the CNT was 10 μm to 55 μm, and the specific surface area was 173 m 2 / g.

[0142] (2) Manufacture of Lithium Secondary Battery A negative electrode slurry containing 93% by weight of natural graphite as a negative electrode active material, 5% by weight of flake type graphite (KS6) as a conductive material, 1% by weight of styrene-butadiene rubber (SBR) as a binder, and 1% by weight of carboxymethyl cellulose (CMC) as a thickener was produced. The negative electrode slurry was coated on a copper substrate, dried and rolled to manufacture a negative electrode.

[0143] Fourteen of the positive electrodes and fifteen of the negative electrodes were each notched to a predetermined size and laminated, and a separator (polyethylene, thickness 25 μm) was interposed between the positive electrode and the negative electrode to form an electrode cell. Thereafter, the tab portions of the positive electrode and the negative electrode were welded respectively. The welded positive electrode / separator / negative electrode combination was placed in a pouch, and three sides except the electrolyte injection surface were sealed. At this time, the portion having the electrode tab was included in the seal portion. Electrolyte was injected from the electrolyte injection surface, the electrolyte injection surface was also sealed, and then it was impregnated for 12 hours or more to manufacture a lithium secondary battery.

[0144] The electrolyte used was a 1M LiPF6 solution prepared using a mixed solvent of EC / EMC (25 / 75; volume ratio), to which 1% by weight of vinylene carbonate (VC) and 0.5% by weight of 1,3-propane sultone (PRS) were added based on the total weight of the solution.

[0145] The lithium secondary battery was pre-charged for 36 minutes at a current corresponding to 0.25C (5A). Degassing was performed 1 hour later, and after aging for 24 hours or more, formation charge and discharge were carried out (charging conditions: CC-CV 0.2C 4.2V 0.05C CUT-OFF, discharging conditions: CC 0.2C 2.5V CUT-OFF).

[0146] Example 2 The preliminary cathode active material was mixed with an aqueous solution containing Ti, Zr, Ba, and Co, and fired at 200 °C to produce a second-1 cathode active material having Ti, Zr, Ba, and Co coated on the surface portion.

[0147] A cathode and a lithium secondary battery were produced in the same manner as in Example 1, except that an aqueous solution of Ti, Al, Zr, and B was used as the coating / doping solution during the production of the first cathode active material, and the second-1 cathode active material was used instead of the second cathode active material during the production of the second cathode active material layer.

[0148] Example 3 The preliminary cathode active material was mixed with an aqueous solution containing Al, Zr, and Co, and fired at 200 °C to produce a second-2 cathode active material.

[0149] A cathode and a lithium secondary battery were produced in the same manner as in Example 1, except that an aqueous solution of Al, Zr, and B was used as the coating / doping solution during the production of the first cathode active material layer, and a mixture of the first cathode active material and the second-2 cathode active material in a weight ratio of 6:4 was used instead of the second cathode active material during the production of the second cathode active material layer.

[0150] Example 4 A cathode and a lithium secondary battery were produced in the same manner as in Example 1, except that the first cathode slurry was produced by mixing the first cathode active material, carbon black as a punctiform conductive material, and PVDF as a binder in a mass ratio of 97:1:2.

[0151] Example 5 A positive electrode and a lithium secondary battery were produced in the same manner as in Example 1, except that the same amount of CNTs was used instead of carbon black.

[0152] Example 6 A positive electrode and a lithium secondary battery were produced in the same manner as in Example 1, except that the same amount of carbon black was used instead of CNTs.

[0153] Example 7 A positive electrode and a lithium secondary battery were produced in the same manner as in Example 1, except that the second positive electrode active material, carbon nanotubes (CNTs) as a linear conductive material, and PVDF as a binder were mixed at a mass ratio of 93:5:2 to produce a second positive electrode slurry.

[0154] Example 8 A positive electrode and a lithium secondary battery were produced in the same manner as in Example 1, except that the first positive electrode active material, carbon black as a dot-like conductive material, and PVDF as a binder were mixed at a mass ratio of 93:5:2 to produce a first positive electrode slurry.

[0155] Example 9 A positive electrode and a lithium secondary battery were produced in the same manner as in Example 1, except that the second positive electrode active material, carbon nanotubes (CNTs) as a linear conductive material, and PVDF as a binder were mixed at a mass ratio of 97:1:2 to produce a second positive electrode slurry.

[0156] Examples 10 to 13 A positive electrode and a lithium secondary battery were produced in the same manner as in Example 1, except that the boron content with respect to the total weight of the first positive electrode active material was adjusted as shown in Table 1.

[0157] Comparative Example 1 A positive electrode and a lithium secondary battery were produced in the same manner as in Example 1, except that the second positive electrode active material layer was not formed (single-layer positive electrode active material layer), and the preliminary positive electrode active material containing no boron was used as the first positive electrode active material.

[0158] Comparative Example 2 A positive electrode and a lithium secondary battery were produced in the same manner as in Example 1, except that the second positive electrode active material layer was not formed (positive electrode active material layer having a single layer structure).

[0159] Comparative Example 3 A positive electrode and a lithium secondary battery were produced in the same manner as in Example 1, except that the spare positive electrode active material not containing boron was used as the first positive electrode active material.

[0160] Comparative Example 4 The preliminary positive electrode active material was mixed with an aqueous boron solution and baked at 200° C. to prepare a second positive electrode active material having a boron coating on the surface thereof. The content of the coating was 1.5 wt % based on the weight of the second positive electrode active material.

[0161] A positive electrode and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-boron-coated preliminary positive electrode active material was used as a first positive electrode active material, and the 2-3 positive electrode active material was used as a second positive electrode active material.

[0162] Comparative Example 5 A positive electrode and a lithium secondary battery were produced in the same manner as in Example 1, except that the same amount of CNTs was used instead of carbon black during the production of the first positive electrode active material layer, and the same amount of carbon black was used instead of CNTs during the production of the second positive electrode active material layer.

[0163] Experimental Example (1) Measurement of the first Raman peak intensity ratio and the second Raman peak intensity ratio The positive electrodes manufactured according to the above examples and comparative examples were cut into samples. The second positive electrode active material layer, which was the outermost layer of the sample, was measured for a second Raman peak intensity ratio using a 532 nm laser Raman spectroscopy (model name: Invia, manufacturer: RENISHAW).

[0164] The specific measurement method of the Raman analyzer is as follows. i) Turned on the power of the Raman analyzer. ii) Opened the Spectral acquisition setup window. iii) Selected "Static" as the Grating Scan Type and entered 1000 (Raman Shift (cm -1 )) as the Center value. iv) In the Configuration, selected 532nm edge as the laser, 1800 / mm (vis) as the grating, and Renishaw 1024 StreamLine CCD as the detector. v) In the Acquisition condition settings, set the Exposure time (s) to 10, the Objective to 50, the Accumulation to 5, the Laser power (%) to 10, and the scan to 20 times. vi) After positioning the sample on the sample stage and confirming the measurement site, the Raman spectroscopy spectrum of the sample was obtained.

[0165] The peak intensity (ID2) at the band (for example, the D band) with a wavenumber of 1300 cm -1 ~1400 cm -1 in the Raman spectroscopy spectrum, and the peak intensity (IG2) at the band (for example, the G band) with a wavenumber of 1550 cm -1 ~1650 cm -1 were measured. The measured peak intensities were applied to Equation 2 to calculate the second Raman peak intensity ratio.

[0166] 3M tape was repeatedly adhered and detached to the upper surface of the sample to partially remove the second cathode active material layer. For the first cathode active material layer separated from the cathode by adhering to the 3M tape, a Raman spectroscopy spectrum was obtained using the same apparatus and the same method as the measurement of the second Raman peak intensity ratio.

[0167] The wavenumber in the Raman spectroscopy spectrum is 1300 cm-1 ~1400 cm -1 The peak intensity (ID1) in the band (e.g., D band) of ~1550 cm -1 ~1650 cm -1 and the peak intensity (IG1) in the band (e.g., G band) of were measured. The measured peak intensities were applied to Equation 1 to calculate the first Raman peak intensity ratio.

[0168] (2) Evaluation of capacity retention rate For the lithium secondary batteries of the above Examples and Comparative Examples, charging (CC-CV 0.5C 4.3V 0.05C CUT-OFF) and discharging (CC 1.0C 2.5V CUT-OFF) were repeated 200 times in a chamber at 25 °C, and the discharge capacity at 200 cycles was divided by the discharge capacity at one cycle and multiplied by 100 to evaluate it as the general capacity retention rate.

[0169] (3) Evaluation of high-temperature resistance increase rate For the lithium secondary batteries of the above Examples and Comparative Examples, charging and discharging were repeated 200 times in the same manner as in Experimental Example (2) in a chamber at 45 °C.

[0170] For the lithium secondary battery after one discharge, the DCIR was measured for 10 seconds at a SOC of 50%, and for the lithium secondary battery after 200 discharges, the DCIR was measured for 10 seconds at a SOC of 50%. The DCIR after 200 discharges was divided by the DCIR after one discharge and multiplied by 100 to evaluate it as the high-temperature resistance increase rate. The results of the measurement and evaluation are shown in Tables 1 and 2 below.

[0171] The content of the coating with respect to the weight of the first positive electrode active material and the types of conductive materials in each layer are shown in Table 1 below.

[0172] In Table 1, "dot-like" indicates a dot-like conductive material (carbon black), and "linear" indicates a linear conductive material (CNT).

[0173]

Table 1

[0174]

Table 2

[0175] Referring to Table 1 and Table 2, in the examples having a two-layer structure, where the first positive electrode active material layer contains a first positive electrode active material containing a boron coating and the first Raman peak intensity ratio is smaller than the second Raman peak intensity ratio, the capacity retention rate was improved and the high-temperature resistance increase rate was decreased as compared with the comparative examples.

[0176] In Example 4 where the first Raman peak intensity ratio was less than 0.5, the capacity retention rate was relatively decreased as compared with other examples.

[0177] In Examples 5 and 8 where the first Raman peak intensity ratio exceeded 1.1, the high-temperature resistance increase rate was relatively increased as compared with other examples.

[0178] In Examples 6 and 9 where the second Raman peak intensity ratio was less than 1.0, the capacity retention rate was relatively decreased as compared with other examples.

[0179] In Example 7 where the second Raman peak intensity ratio exceeded 1.2, the high-temperature resistance increase rate was relatively increased as compared with other examples.

[0180] In Example 12 where the content of the boron-containing coating was less than 0.5% by weight based on the weight of the first positive electrode active material, the capacity retention rate was relatively decreased and the high-temperature resistance increase rate was increased as compared with other examples.

[0181] In Example 13 where the content of the boron-containing coating exceeded 3.0% by weight based on the weight of the first positive electrode active material, the capacity retention rate was relatively decreased as compared with other examples.

Claims

1. a positive current collector, a first positive electrode active material layer disposed on at least one surface of the positive current collector and containing a first positive electrode active material, a second positive electrode active material layer disposed on the first positive electrode active material layer and containing a second positive electrode active material different from the first positive electrode active material, wherein the first positive electrode active material contains boron, a positive electrode for a lithium secondary battery, wherein a first Raman peak intensity ratio defined by the following formula 1 is smaller than a second Raman peak intensity ratio defined by the following formula 2. [Formula 1] First Raman peak intensity ratio = ID1 / IG1 [Formula 2] Second Raman peak intensity ratio = ID2 / IG2 (In Formula 1 and Formula 2, ID1 is the maximum peak intensity in the wavenumber range of 1300 cm －１ to 1400 cm －１ , IG1 is the maximum peak intensity in the wavenumber range of 1550 cm －１ to 1650 cm －１ , ID2 is the maximum peak intensity in the wavenumber range of 1300 cm －１ to 1400 cm －１ , and IG2 is the maximum peak intensity in the wavenumber range of 1550 cm －１ to 1650 cm －１ .)

2. The positive electrode for a lithium secondary battery according to claim 1, wherein the first positive electrode active material further contains at least one of titanium, aluminum, barium, cobalt, and zirconium.

3. The positive electrode for a lithium secondary battery according to claim 1, wherein the second positive electrode active material does not contain boron.

4. The positive electrode for a lithium secondary battery according to claim 1, wherein the first Raman peak intensity ratio is 0.5 to 1.

1.

5. The positive electrode for a lithium secondary battery according to claim 1, wherein the second Raman peak intensity ratio is 1.0 to 1.

2.

6. The positive electrode for a lithium secondary battery according to claim 1, wherein the first positive electrode active material layer and the second positive electrode active material layer each further contain a dot-shaped conductive material or a linear conductive material.

7. The positive electrode for a lithium secondary battery according to claim 6, wherein the first positive electrode active material layer contains the dot-shaped conductive material, and the second positive electrode active material layer contains the linear conductive material.

8. The dot-shaped conductive material is at least one selected from the group consisting of graphite, carbon black, graphene, tin, tin oxide, titanium oxide, LaSrCoO ３ and LaSrMnO ３ The positive electrode for a lithium secondary battery according to claim 6, comprising at least one selected from the group consisting of

9. The positive electrode for a lithium secondary battery according to claim 6, wherein the linear conductive material includes carbon nanotubes.

10. The positive electrode for a lithium secondary battery according to claim 1, wherein the content of boron is 0.5% by weight to 3% by weight based on the weight of the first positive electrode active material.

11. A lithium secondary battery including the positive electrode for a lithium secondary battery according to claim 1, and a negative electrode facing the positive electrode.

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