Positive electrode for rechargeable lithium batteries and rechargeable lithium batteries

Abstract

The present invention relates to a positive electrode for a rechargeable lithium batteries and rechargeable lithium batteries, the positive electrode comprising: a positive electrode current collector; and a positive electrode active material layer positioned on the positive electrode current collector and containing a positive electrode active material and pseudo boehmite. The purpose of the present invention is to improve the stability of the rechargeable lithium batteries by reducing the amount of heat generation and blocking or delaying thermal runaway, during an abnormal reaction of the batteries.

Description

Cathode for lithium secondary batteries and lithium secondary batteries

[0001] It relates to a cathode for a lithium secondary battery and a lithium secondary battery.

[0002] Lithium secondary batteries, which boast high energy density and portability, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research is underway to utilize high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles, or as power storage devices.

[0003] To develop lithium secondary batteries suitable for these applications, various cathode active materials are being studied. Among them, lithium nickel oxide, lithium nickel manganese cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium cobalt oxide are mainly used as cathode active materials.

[0004] Lithium secondary batteries can suffer from short circuits due to various causes, which can generate heat and lead to thermal runaway. Therefore, research is needed to improve battery safety.

[0005] Improves the safety of lithium secondary batteries by reducing the amount of heat generated and blocking or delaying thermal runaway in the event of an abnormal reaction in the battery.

[0006] In one embodiment, a positive electrode for a lithium secondary battery is provided, comprising a positive electrode current collector, and a positive electrode active material layer positioned on the positive electrode current collector and including a positive electrode active material and pseudo Boehmite.

[0007] In another embodiment, a lithium secondary battery is provided including the positive electrode, the negative electrode, and the electrolyte.

[0008] According to one embodiment, the cathode can improve the safety of a lithium secondary battery by reducing the amount of heat generated during an abnormal reaction and blocking or delaying thermal runaway.

[0009] Figures 1 to 4 are cross-sectional views schematically showing a lithium secondary battery according to one embodiment.

[0010] Figure 5 is a schematic drawing showing a cross-section of a positive electrode according to an embodiment.

[0011] Figure 6 is a differential scanning calorimetry (DSC) analysis graph for pseudo boehmite and universal boehmite of Example 1.

[0012] Below, specific implementation examples are described in detail to facilitate their implementation by those skilled in the art. However, the present invention may be implemented in various different forms and is not limited to the implementation examples described herein.

[0013] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0014] Here, “combination of these” means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of the components.

[0015] It should be understood that the terms "include," "comprising," or "having" herein are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0016] To clearly illustrate various layers and regions in the drawings, their thicknesses are enlarged, and similar parts are designated by the same drawing reference numerals throughout the specification. When an element such as a layer, film, region, or plate is said to be "over" or "on" another element, this includes not only the case where it is "directly over" the other element, but also the case where there are other elements in between. Conversely, when an element is said to be "directly over" another element, it means that there are no other elements in between.

[0017] Also, here, “layer” includes not only the shape formed on the entire surface when observed in a plan view, but also the shape formed on a portion of the surface.

[0018] The average particle size can be measured by methods well known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with transmission electron microscope images or scanning electron microscope images. Alternatively, the average particle size can be obtained by measuring using dynamic light scattering, performing data analysis, counting the number of particles for each particle size range, and calculating from the counted number. Unless otherwise defined, the average particle size is the diameter (D) of the particles in the particle size distribution that have a cumulative volume of 50% by volume. 50 ) can mean. In addition, unless otherwise defined, the average particle size is obtained by measuring the size (diameter or length of major axis) of about 20 particles randomly in a scanning electron microscope image to obtain a particle size distribution, and the diameter (D) of the particle having a cumulative volume of 50% by volume in the particle size distribution 50 ) may be taken as the average particle diameter.

[0019] “Or” is not interpreted as exclusive, for example, “A or B” is interpreted as including A, B, A+B, etc.

[0020] “Metal” is interpreted as a concept that includes common metals, transition metals, and metalloids (semi-metals).

[0021] anode

[0022] In one embodiment, a positive electrode for a lithium secondary battery is provided, comprising a positive electrode current collector, and a positive electrode active material layer positioned on the positive electrode current collector and including a positive electrode active material and pseudoboehmite.

[0023] Unlike general boehmite, pseudoboehmite may contain hydroxyl groups, carboxyl groups, or a combination thereof on the particle surface. Such pseudoboehmite may exhibit a maximum endothermic peak in the temperature range of 60°C to 200°C in differential scanning calorimetry (DSC) analysis, for example, in the temperature ranges of 60°C to 180°C, 70°C to 160°C, 80°C to 140°C, and 90°C to 120°C. This means that it can function as a heat absorber in the corresponding temperature range. General boehmite does not exhibit an endothermic peak in the range of 60°C to 200°C, and therefore, it is difficult to function as a heat absorber. It has been confirmed that the pseudoboehmite can reduce the amount of heat generated by inducing an endothermic reaction when the temperature of the battery increases due to an abnormal reaction. In the DSC analysis of the positive electrode including the above pseudoboehmite, the calorific value at the first peak may be 120 J / g or less, for example, 110 J / g or less, 100 J / g or less, 50 J / g to 100 J / g, or 70 J / g to 90 J / g. In this way, when the temperature of the positive electrode including the pseudoboehmite rises due to an abnormal reaction of the battery, the pseudoboehmite undergoes an endothermic reaction at a temperature of about 200°C or less, thereby reducing the calorific value, thereby improving the thermal stability and fire safety of the lithium secondary battery.

[0024] The BET surface area of ​​the above pseudoboehmite is approximately 200 m 2 / g to 600 m 2 / g can be, for example, 300 m 2 / g to 500 m 2 / g, or 350 m 2 / g to 550 m 2 / g. Here, the BET specific surface area may be a specific surface area calculated by an adsorption isotherm measured by adsorbing water vapor on pseudoboehmite particles, or may be a specific surface area calculated by an adsorption isotherm measured by adsorbing nitrogen on pseudoboehmite particles.

[0025] The above pseudo boehmite may have a particle surface modified with a type of surface treatment agent, and the surface treatment agent may include, for example, a silane coupling agent, a titanate coupling agent, an aluminate coupling agent, a fatty acid surface treatment agent, a phosphonic acid, or a combination thereof.

[0026] The pseudoboehmite may be included in an amount of 0.1 wt% to 5 wt% based on 100 wt% of the positive electrode active material layer, for example, 0.1 wt% to 4 wt%, 0.1 wt% to 3 wt%, or 0.5 wt% to 3 wt%. When the pseudoboehmite is included in the above range, the thermal safety can be effectively improved without reducing the capacity or energy density of the positive electrode.

[0027] The above positive electrode active material may be a general positive electrode active material used in a lithium secondary battery, and may specifically include a lithium transition metal composite oxide.

[0028] The above lithium transition metal composite oxide can be expressed by, for example, any one of the following chemical formulas: Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-cCo b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni b Co c L 1 d G e O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li a NiG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2); Li a FePO4(0.90≤a≤1.8).

[0029] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al or a combination thereof.

[0030] The above lithium transition metal composite oxide may include, for example, a lithium nickel-based composite oxide, a lithium cobalt-based composite oxide, a lithium manganese-based composite oxide, or a combination thereof.

[0031] For example, the positive electrode active material may include a lithium nickel-based composite oxide represented by chemical formula 1, a lithium cobalt-based composite oxide represented by chemical formula 2, or a combination thereof.

[0032] [Chemical Formula 1]

[0033] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0034] In the above chemical formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, 0≤z1≤0.7, 0.9≤x1+y1+z1≤1.1, and 0≤b1≤0.1, and M 1 and M 2 are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0035] [Chemical Formula 2]

[0036] Li a2 Co x2 M 3 y2 O 2-b2 X b2

[0037] In the above chemical formula 2, 0.9≤a2≤1.8, 0.7≤x2≤1, 0≤y2≤0.3, 0.9≤x2+y2≤1.1, and 0≤b2≤0.1, and M 3is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is one or more elements selected from the group consisting of F, P and S.

[0038] In Chemical Formula 1, 0.9≤a1≤1.5, 0.9≤a1≤1.2, or 1.01≤a1≤1.2 may be satisfied, and 0.6≤x1≤1, 0≤y1≤0.4, and 0≤z1≤0.4 may be satisfied, or 0.8≤x1≤1, 0≤y1≤0.2, and 0≤z1≤0.2 may be satisfied. For example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less, based on 100 mol% of metals excluding lithium in the lithium transition metal composite oxide. The high-nickel positive electrode active material may be applied to a high-capacity, high-density lithium secondary battery because it can realize a high capacity.

[0039] In the above chemical formula 2, 0.9≤a2≤1.5, 0.9≤a2≤1.2, or 1.01≤a2≤1.2 may be satisfied, 0.8≤x2≤1, and 0≤y2≤0.2, or 0.9≤x2≤1, and 0≤y2≤0.1 may be satisfied. For example, the positive electrode active material may include a lithium cobalt-based composite oxide, and in this case, excellent capacity and lifespan characteristics may be realized in a high voltage range.

[0040] The above positive electrode active material layer may further include a binder.

[0041] The binder serves to adhere the positive electrode active material particles well to each other and also to adhere the positive electrode active material well to the current collector, and representative examples thereof include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0042] The above positive electrode active material layer may further include a conductive material.

[0043] The conductive material is used to provide conductivity to the electrode, and any material that does not cause a chemical change and is electronically conductive can be used in the battery to be constructed. Examples of conductive materials that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0044] For example, the conductive material in the positive electrode may be carbon nanofibers, carbon nanotubes, or a combination thereof. In this case, even if the content of the conductive material in the positive electrode active material layer is reduced, excellent conductivity can be achieved, and by reducing the content of the conductive material, the capacity can be maximized. For example, when the conductive material is carbon nanofibers, carbon nanotubes, or a combination thereof, it may be included in an amount of 1 wt% or less with respect to 100 wt% of the positive electrode active material layer, and may be included in an amount of, for example, 0.1 to 0.9 wt%.

[0045] The thickness of the positive electrode active material layer may be approximately 10 μm to 300 μm, for example, 20 to 250 μm, or 50 to 200 μm.

[0046] The above positive electrode collector may include, but is not limited to, Al, SUS, etc.

[0047] In one embodiment, when the positive electrode active material layer includes an A side adjacent to the positive electrode current collector and an upper B side not adjacent to the positive electrode current collector, the pseudo boehmite may be distributed more on the B side than on the A side. The A side and the B side may be in contact with each other or may be spaced apart from each other. That is, the pseudo boehmite may be distributed more on the upper side opposite in the thickness direction (for example, the area adjacent to the separator) than on the area adjacent to the current collector. The pseudo boehmite may have a concentration gradient in which the content increases from the A side to the B side, for example. In this way, when the pseudo boehmite is included in a higher content on the upper side, the effect of reducing the amount of heat generated when the temperature rises due to an abnormal reaction of the battery can be further enhanced.

[0048] According to one embodiment, a positive electrode may include a positive electrode current collector, a first layer positioned on the positive electrode current collector and containing a positive electrode active material but not containing pseudoboehmite, and a second layer positioned on the first layer and containing the positive electrode active material and pseudoboehmite. According to this structure, since pseudoboehmite is concentratedly distributed in an upper portion of the positive electrode active material layer that does not contact the current collector, the effect of reducing the amount of heat generated by causing an endothermic reaction of pseudoboehmite when the temperature of the battery rises can be further enhanced.

[0049] The pseudoboehmite may be included in an amount of 0.1 wt% to 5 wt% based on 100 wt% of the second layer, for example, 0.5 wt% to 4 wt%, or 1 wt% to 3 wt%.

[0050] At this time, the thickness ratio of the first layer and the second layer is not particularly limited, but may be, for example, 20:80 to 80:20, for example, 30:70 to 70:30, 40:60 to 80:20, 50:50 to 80:20, or 60:40 to 80:20. By appropriately controlling the thickness of the first layer and the second layer, the safety of the battery can be improved while maximizing the capacity.

[0051] functional layer

[0052] According to one embodiment, the positive electrode may further include a functional layer located between the positive electrode current collector and the positive electrode active material layer and containing a lithium transition metal phosphate. For example, when a short circuit occurs in the battery, the functional layer may induce current to flow in the form of positive electrode active material layer ↔ functional layer ↔ positive electrode current collector instead of directly to the positive electrode current collector, thereby reducing Joule heat, thereby lowering the overall amount of heat generation and further improving the safety of the battery. For example, when the functional layer is included in the positive electrode, the battery may not explode or catch fire in a penetration or impact test and may be maintained in good condition. Furthermore, when the functional layer is included, the phenomenon of the positive electrode current collector being damaged during the rolling process of the positive electrode can be effectively suppressed.

[0053] The functional layer may be positioned on the surface of the positive electrode current collector, or may be positioned between the positive electrode current collector and the positive electrode active material layer. The functional layer may serve to improve the thermal safety of the battery and protect the positive electrode current collector, while at the same time allowing the lithium transition metal phosphate to function as a positive electrode active material, thereby further increasing the capacity.

[0054] The above lithium transition metal phosphate can be represented by Chemical Formula 3, Chemical Formula 4, Chemical Formula 5, Chemical Formula 6, or Chemical Formula 7.

[0055] [Chemical Formula 3]

[0056] Li a3 Fe (1-x3) M3 x3 PO4

[0057] In chemical formula 3, 0.90≤a3≤1.5, 0≤x3≤0.4, and M 3 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof,

[0058] [Chemical Formula 4]

[0059] Li a4 Mn x4 Fe (1-x4-y4) M 4 y4 PO4

[0060] In chemical formula 4, 0.90≤a4≤1.5, 0.1≤x4≤0.9, M 4 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof,

[0061] [Chemical Formula 5]

[0062] Li a5 Mn (1-x5) M 5 x5 PO4

[0063] In chemical formula 5, 0.90≤a5≤1.5, 0≤x5≤0.4, and M 5 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof,

[0064] [Chemical Formula 6]

[0065] Li a6 Ti (2-x6) M 6 x6 (PO4)3

[0066] In chemical formula 6, 0.90≤a6≤1.5, 0≤x6≤0.4, and M 6is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof,

[0067] [Chemical Formula 7]

[0068] Li a7 Ti (1-x7) M 7 x7 PO5

[0069] In chemical formula 7, 0.90≤a7≤1.5, 0≤x7≤0.4, and M 7 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof.

[0070] Lithium transition metal phosphates include LiFePO4, LiMn, and other specific examples. 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 It may include PO4, LiMnPO4, LiTiPO5, LiTi2(PO4)3, or a combination thereof.

[0071] Lithium transition metal phosphate is in particle form, and the average particle diameter (D) of the particles is 50 ) may be 0.01 ㎛ to 2 ㎛, for example 0.1 ㎛ to 1 ㎛, or 0.2 ㎛ to 0.9 ㎛.

[0072] The above functional layer may further include a binder and a conductive material.

[0073] The above binder can serve to adhere the materials within the functional layer to each other and to adhere the functional layer to the current collector. The binder may be an insoluble binder, a water-soluble binder, or a combination thereof.

[0074] The above-mentioned non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, an ethylene propylene copolymer, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0075] The water-soluble binder may be a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber (ABR), acrylic rubber, butyl rubber, fluoroelastomer, and combinations thereof. The polymer resin binder may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0076] When using a water-soluble binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0077] The binder may be included in an amount of 0.1 to 15 wt% based on 100 wt% of the functional layer, for example, 0.5 to 11 wt%, 0.5 to 5 wt%, or 0.5 to 3 wt%.

[0078] The conductive material in the functional layer may be a conductive material including, for example, a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or carbon nanotube; a metal-based material containing copper, nickel, aluminum, or silver in the form of metal powder or metal fiber; a conductive polymer such as a polyphenylene derivative; or a mixture thereof.

[0079] The conductive agent may be included in an amount of 0.1 to 5 wt% based on 100 wt% of the functional layer, for example, 0.1 to 3 wt%, 0.1 to 2 wt%, 0.1 to 1 wt%, or 0.1 to 0.9 wt%.

[0080] For example, the conductive material in the functional layer may be carbon nanofibers, carbon nanotubes, or a combination thereof. In this case, even if the content of the conductive material in the functional layer is reduced, excellent conductivity can be achieved, and by reducing the content of the conductive material, the capacity can be increased and heat resistance can be further improved. For example, when the conductive material is carbon nanofibers, carbon nanotubes, or a combination thereof, it may be included in an amount of 1 wt% or less with respect to 100 wt% of the functional layer, and for example, it may be included in an amount of 0.1 to 0.9 wt%.

[0081] When the functional layer includes a conductive material and a binder, the functional layer may contain 80 to 99.8 wt% of the lithium transition metal phosphate, 0.1 to 15 wt% of the first binder, and 0.1 to 5 wt% of the conductive material, based on 100 wt% of the functional layer. When each component of the functional layer satisfies the above content range, the capacity of the battery can be maximized while improving heat resistance.

[0082] The thickness of the functional layer may be 1 to 30 μm, for example, 1 to 20 μm, 1 to 10 μm, or 2 to 8 μm. When this range is satisfied, the functional layer can sufficiently contribute to ensuring heat resistance, safety, and reliability while minimizing a decrease in energy density while the lithium secondary battery is being operated.

[0083] The area of ​​the functional layer may be equal to or smaller than the area of ​​one side of the positive electrode current collector. For example, the ratio of the area of ​​the functional layer to the area of ​​the positive electrode current collector may be 0.7 to 0.99, or 0.8 to 0.9. Accordingly, a portion of the surface of the positive electrode current collector may be exposed without being covered by the functional layer, and a ceramic insulating layer described below may be applied to a portion of the surface of the positive electrode current collector exposed without the functional layer applied, thereby maximizing the stability of the lithium secondary battery.

[0084] In addition, the area of ​​the functional layer may be equal to or greater than the area of ​​the positive electrode active material layer. For example, the ratio of the area of ​​the functional layer to the area of ​​the positive electrode active material layer may be 1 to 1.5, or 1.1 to 1.4. Accordingly, a portion of the surface of the functional layer may be exposed without being covered by the positive electrode active material layer, and when the battery is short-circuited, current may flow in the form of positive electrode active material ↔ functional layer ↔ positive electrode current collector, thereby inducing a reduction in Joule heat. Accordingly, a lithium secondary battery including the positive electrode may secure safety and reliability while reducing the overall heat generation when a short circuit occurs.

[0085] Ceramic insulating layer

[0086] According to one embodiment, the positive electrode may further include a ceramic insulating layer located on a non-coated portion on the positive electrode current collector layer to which the positive electrode active material layer (or the functional layer) is not applied.

[0087] The ceramic insulating layer can be said to be a layer that is located on the non-conductive portion of the surface of the positive electrode collector and includes inorganic particles to perform an insulating function.

[0088] The inorganic particles may include, for example, aluminum oxide, silicon dioxide, magnesium oxide, titanium dioxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, or combinations thereof.

[0089] The average particle diameter of the above inorganic particles (D 50 ) may be 0.1 ㎛ to 20 ㎛, for example, 0.1 ㎛ to 10 ㎛, 0.1 ㎛ to 5 ㎛, and for example, may be more than 2 ㎛, for example, 2.1 ㎛ to 5 ㎛. By appropriately adjusting the size of the inorganic particles, the adhesion and heat resistance of the ceramic insulating layer can be improved.

[0090] The inorganic particles may be included in an amount of 50 wt% to 99.9 wt% based on 100 wt% of the ceramic insulating layer, for example, 65 wt% to 99 wt%, 70 wt% to 98 wt%, 80 wt% to 97 wt%, or 90 wt% to 96 wt%. When the inorganic particles are included in the above content range, the ceramic insulating layer can realize excellent insulating performance, heat resistance, and fire safety.

[0091] The above ceramic insulating layer may further include a binder in addition to the inorganic particles.

[0092] The binder can serve to ensure good adhesion of materials within the ceramic insulating layer to each other and to the positive electrode current collector. The binder can be an insoluble binder, a water-soluble binder, or a combination thereof. The description of these materials is the same as that of the binder within the functional layer.

[0093] The above binder may be included in an amount of 0.1 to 15 wt% based on 100 wt% of the above ceramic insulating layer, for example, 4 to 11 wt%.

[0094] The thickness of the ceramic insulating layer may be 5 μm to 100 μm, for example, 5 μm to 80 μm, 5 μm to 60 μm, 10 μm to 50 μm, or 20 μm to 50 μm. In this case, the ceramic insulating layer can sufficiently contribute to the insulating effect during operation of the lithium secondary battery.

[0095] The area of ​​the ceramic insulating layer may be smaller than the area of ​​the positive electrode current collector. For example, the ratio of the area of ​​the ceramic insulating layer to the area of ​​the positive electrode current collector may be 0.01 to 0.3, or 0.1 to 0.2.

[0096] For example, the ceramic insulating layer and the functional layer may be spaced apart from each other or may be in contact with each other. Similarly, the ceramic insulating layer and the positive electrode active material layer may be spaced apart from each other or may be in contact with each other. When each layer is in contact with each other, a mixed region in which the components of each layer are mixed may exist at the interface. When the ceramic insulating layer and each layer are spaced apart from each other, the separation distance between the ceramic insulating layer and the functional layer may be shorter than the separation distance between the ceramic insulating layer and the positive electrode active material layer.

[0097] lithium secondary battery

[0098] In one embodiment, a lithium secondary battery is provided comprising the aforementioned positive electrode, negative electrode, and electrolyte. As an example, the lithium secondary battery may comprise a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrolyte.

[0099] Lithium secondary batteries can be classified into cylindrical, square, pouch, coin, etc. shapes according to their form. FIGS. 1 to 4 are schematic diagrams illustrating lithium secondary batteries according to one embodiment, wherein FIG. 1 can be said to be a circular battery shape, FIG. 2 a square battery shape, and FIGS. 3 and 4 a pouch battery shape. Referring to FIGS. 1 to 4, a lithium secondary battery (100) may include an electrode assembly (40) having a separator (30) interposed between a positive electrode (10) and a negative electrode (20), and a case (50) in which the electrode assembly (40) is built. The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown). The lithium secondary battery (100) may include a sealing member (60) that seals the case (50) as shown in FIG. 1. In addition, in FIG. 2, the lithium secondary battery (100) may include a positive lead tab (11), a positive terminal (12), a negative lead tab (21), and a negative terminal (22). As in FIGS. 3 and 4, the lithium secondary battery (100) may include electrode tabs (70), i.e., a positive tab (71) and a negative tab (72), which serve as electrical paths for inducing current formed in the electrode assembly (40) to the outside.

[0100] cathode

[0101] The negative electrode may include a current collector and a negative electrode active material layer positioned on the current collector, and the negative electrode active material layer includes a negative electrode active material and may further include a binder, a conductive material, or a combination thereof.

[0102] Negative active material

[0103] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0104] The material capable of reversibly intercalating / deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0105] As the above lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0106] As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, silicon-carbon composite, SiOx(0 <x<2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소(Si를 제외함), 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합에서 선택되는 원소이며, 예컨대 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, 및 이들의 조합에서 선택됨), 또는 이들의 조합일 수 있다. 상기 Sn계 음극 활물질로는 Sn, SnO2, Sn 합금 또는 이들의 조합일 수 있다.

[0107] The above silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle diameter (D) of the silicon-carbon composite particles50 ) may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it may include secondary particles (cores) in which silicon primary particles are assembled and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the silicon primary particles, so that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0108] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles, and an amorphous carbon coating layer positioned on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon may include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0109] When the above silicon-carbon composite includes silicon and amorphous carbon, the content of silicon may be 10 wt% to 50 wt%, and the content of amorphous carbon may be 50 wt% to 90 wt%, based on 100 wt% of the silicon-carbon composite. In addition, when the composite includes silicon, amorphous carbon, and crystalline carbon, the content of silicon may be 10 wt% to 50 wt%, the content of crystalline carbon may be 10 wt% to 70 wt%, and the content of amorphous carbon may be 20 wt% to 40 wt%, based on 100 wt% of the silicon-carbon composite.

[0110] In addition, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle diameter (D) of the silicon particles (primary particles) 50) may be 10 nm to 1 ㎛, or 10 nm to 200 nm. The silicon particles may exist as silicon alone, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is SiO x (0 <x<2)로 표시될 수 있다. 이때, 산화 정도를 나타내는 Si:O의 원자 함량 비율은 99:1 내지 33:67일 수 있다. 본 명세서에서, 별도의 정의가 없는 한, 평균 입경(D 50 ) means the diameter of the particle whose cumulative volume is 50% by volume in the particle size distribution.

[0111] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material. When the Si-based negative electrode active material or Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio can be 1:99 to 90:10 by weight.

[0112] bookbinder

[0113] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0114] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0115] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0116] When using an aqueous binder as the cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0117] The dry binder is a polymeric material capable of being fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0118] Challenge

[0119] Conductive materials are used to impart conductivity to electrodes, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, and silver in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0120] The content of the negative active material may be 95 wt% to 99.5 wt% with respect to 100 wt% of the negative active material layer, and the content of the binder may be 0.5 wt% to 5 wt% with respect to 100 wt% of the negative active material layer. For example, the negative active material layer may include 90 wt% to 99 wt% of the negative active material, 0.5 wt% to 5 wt% of the binder, and 0.5 wt% to 5 wt% of the conductive material.

[0121] Whole house

[0122] The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, and may be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0123] electrolyte

[0124] An electrolyte for a lithium secondary battery may be, for example, an electrolyte solution, which may include a non-aqueous organic solvent and a lithium salt.

[0125] Non-aqueous organic solvents serve as a medium through which ions involved in the electrochemical reactions of a battery can move. Non-aqueous organic solvents can be carbonate, ester, ether, ketone, or alcohol solvents, aprotic solvents, or combinations thereof.

[0126] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, and caprolactone. Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. In addition, examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol, and examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0127] Non-aqueous organic solvents can be used alone or in combination of two or more, and when two or more are used in combination, the mixing ratio can be appropriately adjusted depending on the desired battery performance, which is widely understood by those working in the relevant field.

[0128] When using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0129] The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent. For example, a carbonate-based solvent and an aromatic hydrocarbon-based organic solvent may be mixed and used in a volume ratio of 1:1 to 30:1.

[0130] The electrolyte may further contain vinylethyl carbonate, vinylene carbonate or ethylene carbonate compounds to improve battery life.

[0131] Representative examples of the above ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0132] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions in the battery, enabling the basic operation of lithium secondary batteries and promoting the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), lithium bis(oxalato)borate (LiBOB).

[0133] It is recommended that the concentration of lithium salt be within the range of 0.1 M to 2.0 M. When the concentration of lithium salt is within the above range, the electrolyte can exhibit excellent performance due to its appropriate ionic conductivity and viscosity, and lithium ions can move effectively.

[0134] separator

[0135] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films comprising two or more layers thereof. Furthermore, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0136] The above separator may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof, positioned on one or both sides of the porous substrate.

[0137] The above porous substrate may be a polymer film formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyarylether ketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more thereof.

[0138] The porous substrate may have a thickness of about 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0139] The organic material may include a (meth)acrylic copolymer comprising a first structural unit derived from (meth)acrylamide, and a second structural unit comprising at least one of a structural unit derived from (meth)acrylic acid or a (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0140] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include inorganic particles selected from SrTiO3, BaTiO3, Mg(OH)2, boehmite and combinations thereof, but is not limited thereto. The average particle diameter (D) of the inorganic particles 50 ) can be from 1 nm to 2000 nm, for example, from 100 nm to 1000 nm, from 100 nm to 700 nm.

[0141] The organic and inorganic substances may be mixed and present in one coating layer, or a coating layer including an organic substance and a coating layer including an inorganic substance may be present in a laminated form.

[0142] The thickness of the above coating layer may be 0.5 ㎛ to 20 ㎛, for example, 1 ㎛ to 10 ㎛, or 1 ㎛ to 5 ㎛.

[0143] Hereinafter, examples and comparative examples of the present invention are described. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0144] Example 1

[0145] 1. Manufacturing of the anode

[0146] A functional layer slurry was prepared by mixing 98 wt% LiFeO4 as a lithium transition metal phosphate, 1.5 wt% polyvinylidene fluoride as a binder, and 0.5 wt% carbon nanotubes as a conductive material in an N-methylpyrrolidone (NMP) solvent. This was applied to one surface of an aluminum current collector using a micrograver facility and dried to form a 4 ㎛ thick functional layer.

[0147] A slurry was prepared by mixing 98 wt% of LiCoO2 as a positive electrode active material, 1.5 wt% of polyvinylidene fluoride as a binder, and 0.5 wt% of carbon nanotubes as a conductive material in an NMP solvent, which was then applied onto a safety functional layer and dried to form a first layer of a positive electrode active material layer having a thickness of approximately 50 μm.

[0148] Next, 97 wt% of LiCoO2 as a cathode active material, 1.5 wt% of polyvinylidene fluoride as a binder, 0.5 wt% of carbon nanotubes as a conductive material, and pseudo boehmite (BET) 1 : 407 m 2 / g, BET 2 : 377 m 2 / g, CIS Chemical Co., Ltd.) was mixed in an NMP solvent to prepare a slurry, which was applied onto the first layer and dried to form a second layer having a thickness of about 50 μm.

[0149] A ceramic insulating layer slurry was prepared by mixing 90 wt% of boehmite as a ceramic particle and 10 wt% of polyvinylidene fluoride as a binder in a water solvent. On one side of the aluminum current collector to which the functional layer, the first layer, and the second layer were applied, the ceramic insulating layer slurry was applied using a gravure coater to the uncoated area of ​​one end to which these layers were not applied, and dried to form a ceramic insulating layer having a thickness of 10 μm.

[0150] 2. Manufacturing of lithium secondary batteries

[0151] An electrode assembly was manufactured by interposing a polytetrafluoroethylene separator between the prepared positive electrode and the lithium metal counter electrode, inserting it into a case, and injecting an electrolyte solution containing 1 M LiPF6 dissolved in a solvent mixed with ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7, thereby manufacturing a half-cell in a conventional manner.

[0152] Example 2

[0153] A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the content of pseudoboehmite in the second layer of the positive electrode active material layer was changed to 2 wt% and the content of the positive electrode active material was changed to 96 wt%.

[0154] Example 3

[0155] A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the content of pseudoboehmite in the second layer of the positive electrode active material layer was changed to 3 wt% and the content of the positive electrode active material was changed to 95 wt%.

[0156] Example 4

[0157] A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 3, except that the order of the first and second layers of the positive electrode active material layer was changed and the functional layer, second layer, and first layer were laminated in that order.

[0158] Comparative Example 1

[0159] A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that only the first layer was formed to a thickness of approximately 100 μm without forming a second layer in the positive electrode active material layer.

[0160] The bipolar design details of the examples and comparative examples are briefly shown in Table 1 below.

[0161] Functional layer 1st layer 2nd layer PB content (weight %) Anode DSC (J / g, 1) stPeak) Penetration safety Maximum penetration temperature (℃) Example 1 LFPLCOLCO+PB1870.K101 Example 2 LFPLCOLCO+PB2850.K102 Example 3 LFPLCOLCO+PB3860.K81 Example 4 LFPLCOLCO+PBLCO3990.K109 Comparative example 1 LFPLCOLCO0128 N.G≥ 300

[0162] Evaluation Example 1: DSC

[0163] First, differential scanning calorimetry (DSC) analysis was performed on the positive electrode of Example 1 using pseudoboehmite and the positive electrode using general-purpose boehmite, respectively, and the results are shown in Fig. 6. Referring to Fig. 6, the general-purpose boehmite does not exhibit an endothermic peak in the temperature range below 400°C, whereas the pseudoboehmite of the Example exhibits a strong endothermic peak at about 100°C. Accordingly, it is thought that the pseudoboehmite of the Example can function as an endothermic material by inducing an endothermic reaction around 100°C, thereby preventing overheating in the event of an abnormal reaction of the battery and improving safety.

[0164] In addition, DSC analysis was performed on the positive electrodes manufactured in Examples 1 to 4 and Comparative Example 1 to calculate the amount of heat generated at the first peak, and the results are shown in Table 1 above.

[0165] Referring to Table 1 above, in the case of Comparative Example 1, the calorific value at the first peak was high at 128 J / g, while Examples 1 to 4 showed significantly lower calorific values. Accordingly, it was confirmed that in the cases of the Examples, when the temperature rapidly rises due to an abnormal reaction of the battery and the materials within the positive electrode react, the calorific value within the positive electrode can be reduced, thereby improving thermal safety and fire safety.

[0166] Evaluation Example 2: Penetration Evaluation

[0167] After fully charging the half-cells of Examples 1 to 4 and Comparative Example 1 to 4 at 4.45 V, an experiment was conducted to completely penetrate the center of the battery at a penetration speed of 5 mm / s and a pin thickness of 2.5 mmΦ. At this time, the maximum temperature inside the battery was measured and shown in Table 1 above. If there was no effect on the appearance of the battery or the external temperature was less than 150°C, it was judged as OK, and if the external temperature was 150°C or higher or there was an abnormal reaction such as smoke, flame, or explosion, it was judged as NG and the results were shown in Table 1 above.

[0168] Referring to the results in Table 1 above, in the case of Comparative Example 1, the maximum temperature upon penetration exceeded 300°C and abnormal effects such as flames were observed, whereas in the cases of the Examples, the maximum temperature upon penetration was within a low range of 109°C or less and the Examples also passed the penetration safety evaluation. This shows that the batteries of the Examples have improved safety.

[0169] Evaluation Example 3: Battery Performance Evaluation

[0170] For the batteries manufactured in Examples 1 and 3, an initial charge / discharge was performed by charging to 4.47 V at 0.2 C, then cutting off at 0.02 C for an initial charge, and then initially discharging to 2.75 V at 0.2 C. Subsequently, the batteries were charged to 4.16 V at 1.3 C, then cut off at 1.0 C, then charged to 4.28 V at 1.0 C, then cut off at 0.8 C, then charged to the maximum voltage at 0.8 C, then cut off at 0.1 C for an initial charge, and then discharged to 3.2 V at 0.5 C. This cycle was repeated 1200 times. Figure 7 shows the discharge capacity retention rate (left vertical axis) according to the number of cycles, and the thickness change rate (right vertical axis) of the batteries. Referring to FIG. 7, it can be confirmed that both Examples 1 and 3 have excellent capacity retention rates up to 1200 cycles and exhibit low thickness change rates, thereby achieving excellent electrochemical performance.

[0171] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention.

[0172] [Explanation of symbols]

[0173] 100: Lithium secondary battery 10: Cathode

[0174] 11: Positive lead tab 12: Positive terminal

[0175] 20: Negative lead tab 21: Negative lead tab

[0176] 22: Negative terminal 30: Separator

[0177] 40: Electrode assembly 50: Case

[0178] 60: Sealing member 70: Electrode tab

[0179] 71: Positive tab 72: Negative tab

Claims

1. Anode current collector, and A positive electrode for a lithium secondary battery comprising a positive electrode active material layer positioned on the positive electrode current collector and including a positive electrode active material and pseudoboehmite.

2. In paragraph 1, The above pseudoboehmite is a positive electrode for a lithium secondary battery that exhibits a maximum endothermic peak in a temperature range of 60°C to 200°C in differential scanning calorimetry (DSC).

3. In paragraph 1, The above pseudoboehmite contains hydroxyl groups, carboxyl groups, or a combination thereof on the particle surface, and has a BET specific surface area of ​​200 m 2 / g to 600 m 2 / g positive electrode for lithium secondary battery.

4. In paragraph 1, A positive electrode for a lithium secondary battery, wherein the pseudoboehmite is included in an amount of 0.1 wt% to 5 wt% based on 100 wt% of the positive electrode active material layer.

5. In paragraph 1, The above positive electrode active material includes a lithium transition metal composite oxide, The above lithium transition metal composite oxide is a positive electrode for a lithium secondary battery comprising a lithium nickel-based composite oxide, a lithium cobalt-based composite oxide, a lithium manganese-based composite oxide, or a combination thereof.

6. In paragraph 1, The positive electrode active material is a positive electrode for a lithium secondary battery comprising a lithium nickel-based composite oxide represented by chemical formula 1, a lithium cobalt-based composite oxide represented by chemical formula 2, or a combination thereof: [Chemical Formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In the above chemical formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, 0≤z1≤0.7, 0.9≤x1+y1+z1≤1.1, and 0≤b1≤0.1, and M 1 and M 2 are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S, [Chemical Formula 2] Li a2 Co x2 M 3 y2 O 2-b2 X b2 In the above chemical formula 2, 0.9≤a2≤1.8, 0.7≤x2≤1, 0≤y2≤0.3, 0.9≤x2+y2≤1.1, and 0≤b2≤0.1, and M 3 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is one or more elements selected from the group consisting of F, P and S.

7. In paragraph 1, The above positive electrode active material layer includes an A side adjacent to the positive electrode current collector and an upper B side not adjacent to the positive electrode current collector, A positive electrode for a lithium secondary battery in which the above pseudoboehmite is distributed more on the B side than on the A side.

8. In paragraph 1, A positive electrode for a lithium secondary battery having a concentration gradient in which the content of pseudoboehmite increases from side A to side B.

9. In paragraph 1, positive current collector, A first layer located on the positive electrode current collector and containing a positive electrode active material but not containing pseudoboehmite, and A positive electrode for a lithium secondary battery comprising a second layer positioned on a first layer and containing a positive electrode active material and pseudoboehmite.

10. In paragraph 9, A positive electrode for a lithium secondary battery, wherein the pseudoboehmite is included in an amount of 0.1 wt% to 5 wt% based on 100 wt% of the second layer.

11. In paragraph 9, A positive electrode for a lithium secondary battery, wherein the thickness ratio of the first layer and the second layer is 20:80 to 80:

20.

12. In paragraph 1, A positive electrode for a lithium secondary battery further comprising a functional layer located between the positive electrode current collector and the positive electrode active material layer and containing a lithium transition metal phosphate.

13. In paragraph 12, The above lithium transition metal phosphate is a positive electrode for a lithium secondary battery represented by Chemical Formula 3, Chemical Formula 4, Chemical Formula 5, Chemical Formula 6, or Chemical Formula 7: [Chemical Formula 3] Li a3 Fe (1-x3) M 3 x3 PO4 In chemical formula 3, 0.90≤a3≤1.5, 0≤x3≤0.4, and M 3 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof, [Chemical Formula 4] Li a4 Mn x4 Fe (1-x4-y4) M 4 y4 PO4 In chemical formula 4, 0.90≤a4≤1.5, 0.1≤x4≤0.9, M 4 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof, [Chemical Formula 5] Li a5 Mn (1-x5) M 5 x5 PO4 In chemical formula 5, 0.90≤a5≤1.5, 0≤x5≤0.4, and M 5 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof, [Chemical Formula 6] Li a6 You (2-x6) M 6 x6 (PO4)3 In chemical formula 6, 0.90≤a6≤1.5, 0≤x6≤0.4, and M 6 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof, [Chemical Formula 7] Li a7 You (1-x7) M 7 x7 PO5 In chemical formula 7, 0.90≤a7≤1.5, 0≤x7≤0.4, and M 7 is Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof.

14. In paragraph 13, The above lithium transition metal phosphates are LiFePO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 A cathode for a lithium secondary battery comprising PO4, LiMnPO4, LiTiPO5, LiTi2(PO4)3, or a combination thereof.

15. In paragraph 13, The thickness of the positive electrode active material layer is 10 ㎛ to 300 ㎛, A positive electrode for a lithium secondary battery, wherein the thickness of the functional layer is 1 ㎛ to 30 ㎛.

16. In paragraph 13, A positive electrode for a lithium secondary battery, wherein the ratio of the area of ​​the positive electrode active material layer to the area of ​​the functional layer is 1 to 1.

5.

17. In paragraph 1, A positive electrode for a lithium secondary battery further comprising a ceramic insulating layer located on a non-coated portion on the positive electrode current collector layer to which the positive electrode active material layer is not applied.

18. In paragraph 17, The above ceramic insulating layer includes inorganic particles and a binder, The above inorganic particles include aluminum oxide, silicon dioxide, magnesium oxide, titanium dioxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, or a combination thereof, The average particle diameter of the above inorganic particles (D 50 ) is a positive electrode for a lithium secondary battery exceeding 2 μm.

19. In paragraph 15, The thickness of the above ceramic insulating layer is 5 ㎛ to 100 ㎛, A positive electrode for a lithium secondary battery, wherein the ceramic insulating layer is spaced apart from or in contact with the positive electrode active material layer.

20. The anode according to any one of paragraphs 1 to 19; cathode, and A lithium secondary battery containing an electrolyte.

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