Positive electrode for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

Disclosed are a positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same, the positive electrode comprising: a positive electrode current collector; the positive electrode comprises a positive electrode current collector, a safety function layer located on the positive electrode current collector, and a positive electrode active material layer located on the safety function layer, and the safety function layer comprises a first safety function layer containing a lithium iron phosphate compound and a second safety function layer containing a heat absorption material.

Description

TECHNICAL FIELD

[0001] Disclosed are a positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same. BACKGROUND

[0002] As electronic devices using batteries, such as mobile phones, laptop computers, electric vehicles, etc., are becoming widespread, the demand for rechargeable batteries having high energy density and high capacity is increasing.

[0003] A rechargeable lithium battery includes an electrolyte and a positive electrode and a negative electrode including an active material capable of intercalating and deintercalating lithium ions, and generates electric energy through oxidation and reduction reactions when lithium ions intercalate / deintercalate from the positive electrode and the negative electrode.

[0004] When a sharp object (e.g., a nail) penetrates a rechargeable lithium battery, a short circuit occurs when the negative electrode and the positive electrode come into contact. This short circuit can cause internal heating in the rechargeable lithium battery and further cause a fire.

[0005] Meanwhile, when a rechargeable lithium battery is exposed to a high-temperature environment, the structure of the positive electrode active material collapses, and oxygen radicals are generated, causing oxidative decomposition of the electrolyte solution. This oxidative decomposition of the electrolyte can be another cause of internal heating and a fire of the rechargeable lithium battery.

[0006] Therefore, a method of reducing or inhibiting internal heating and a fire of a rechargeable lithium battery and ensuring safety in various situations such as penetration by a sharp object and exposure to high temperatures would be advantageous. SUMMARY

[0007] Some example embodiments include a positive electrode that reduces or inhibits internal heating and a fire of a rechargeable lithium battery and ensures safety in various situations such as penetration by a sharp object or exposure to high temperatures.

[0008] Some example embodiments include a rechargeable lithium battery including the positive electrode.

[0009] Some example embodiments include a positive electrode for a rechargeable lithium battery, the positive electrode including a positive electrode current collector, a safety function layer on the positive electrode current collector, and a positive electrode active material layer on the safety function layer, wherein the safety function layer includes a first safety function layer including a lithium iron phosphate-based compound and a second safety function layer including a heat absorbing material.

[0010] Some example embodiments include a rechargeable lithium battery including the positive electrode, a negative electrode, and an electrolyte.

[0011] The positive electrode according to some example embodiments can ensure safety by reducing or suppressing heat generation and ignition of a rechargeable lithium battery in various situations such as penetration by a sharp object or exposure to high temperatures. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figures 1 to 4 is a schematic diagram illustrating a rechargeable lithium battery according to some example embodiments. DETAILED DESCRIPTION

[0013] Hereinafter, example embodiments will be described in detail. However, these embodiments are examples, the present disclosure is not limited thereto, and the present disclosure is defined by the scope of claims.

[0014] As used herein, when a specific definition is not otherwise provided, it will be understood that when an element such as a layer, film, region, or substrate is referred to as "on" another element, it can be directly on the other element or an intervening element can also be present.

[0015] As used herein, the singular can include the plural unless it is clear that it is meant otherwise. In addition, "A or B" can mean "including A, including B, or including A and B" unless otherwise indicated.

[0016] As used herein, "combinations thereof" can mean a stack of components, a composite, a copolymer, an alloy, a blend, and a mixture of reactants.

[0017] As used herein, D50 particle diameter and D90 particle diameter can mean the diameter of particles of which the cumulative volume is 50% by volume (D50) and the diameter of particles of which the cumulative volume is 90% by volume (D90) in a particle size distribution, respectively. The D50 particle diameter and the D90 particle diameter can be measured by a method well known to those skilled in the art, for example, by measuring with a particle size analyzer, a transmission electron microscope, or a scanning electron microscope. Alternatively, data analysis is performed using a dynamic light scattering measuring device, and the number of particles for each particle size range is counted. Thereby, the D50 particle diameter and the D90 particle diameter can be obtained. Laser diffraction method can also be used. When measured by laser diffraction, for example, particles to be measured are dispersed in a dispersion medium using ultrasonic waves of about 28 kHz, then introduced into a commercially available laser diffraction particle size measuring device (for example, MT 3000 available from Microtrac, Inc.), and after irradiation with an output power of 60 W, the D50 particle diameter based on a 50% particle size distribution and the D90 particle diameter based on a 90% particle size distribution in the measuring device can be calculated. When the term "about" or "substantially" is used in connection with a numerical value in the present specification, it means that the relevant numerical value includes a tolerance of ±10% around the stated numerical value. When a range is specified, the range includes all values therebetween, such as all values with an increment of 0.1%.

[0018] Positive electrode Some example embodiments include a positive electrode for a rechargeable lithium battery, the positive electrode including a positive electrode current collector, a safety function layer on the positive electrode current collector, and a positive electrode active material layer on the safety function layer, wherein the safety function layer includes a first safety function layer including a lithium iron phosphate-based compound and a second safety function layer including a heat absorption material.

[0019] A positive electrode according to some example embodiments is obtained by disposing a first safety function layer having a current reduction function when a short circuit occurs and / or is exposed to high temperatures and a second safety function layer having a heat absorption function between a positive electrode current collector and a positive electrode active material layer.

[0020] The lithium iron phosphate-based compound is or includes a positive electrode active material having a high resistance and can reduce current when a short circuit occurs due to penetration of a rechargeable lithium battery by a sharp object.

[0021] In addition, even when heat is generated inside a rechargeable lithium battery due to penetration by a sharp object, exposure to high temperatures, or the like, the heat absorption material, which is a material having a heat absorption function, can absorb the heat.

[0022] Therefore, since a first safety function layer having a current reduction function when a short circuit occurs and / or is exposed to high temperatures and a second safety function layer having a heat absorption function are interposed between a positive electrode current collector and a positive electrode active material layer, a positive electrode according to some example embodiments can ensure safety by reducing or inhibiting heat release and ignition of a rechargeable lithium battery in various situations such as penetration by a sharp object, exposure to high temperatures, or the like.

[0023] The order in which the first safety function layer and the second safety function layer are disposed is not limited, but compared to the order in which the positive electrode current collector / second safety function layer / first safety function layer / positive electrode active material layer is disposed, the order in which the positive electrode current collector / first safety function layer / second safety function layer / positive electrode active material layer is disposed can be desirable.

[0024] For the latter, when penetrated by a sharp object, the first safety function layer can first contact the sharp object and effectively exhibit a current reduction function, and when a short circuit occurs, the second safety function layer can first contact heat generated inside a rechargeable lithium battery and effectively exhibit a heat absorption function.

[0025] Heat-absorbing material The heat absorption material can be or include composite particles including a metal hydroxide and a phosphorus (P)-based flame retardant.

[0026] The metal hydroxide has a heat absorption function, and the phosphorus-based flame retardant has an oxygen radical capturing function and an anti-combustion function.

[0027] Accordingly, the endothermic material captures oxygen radicals generated due to structural collapse of the positive electrode active material when the rechargeable lithium battery is exposed to a high-temperature environment (oxygen radical capturing function), and even when heat is generated inside the rechargeable lithium battery, the endothermic material absorbs heat (endothermic function) and delays combustion of the rechargeable lithium battery to reduce or suppress ignition (anti-combustion function).

[0028] Here, "complex" means that the functional group (e.g., hydroxyl group) of the metal hydroxide and the functional group (e.g., phosphoric acid group) of the phosphorus-based flame retardant are chemically bonded to each other to form a state of a plurality of particles of a single substance.

[0029] In addition, "chemical bond" includes various types of bonds such as covalent bond, ionic bond, coordinate bond, and metallic bond. The bonding between the particles can be confirmed by, for example, X-ray photoelectron spectroscopy.

[0030] In detail, the plurality of metal hydroxide particles and the plurality of phosphorus-based flame retardant particles can be chemically bonded to each other to form secondary particles, and within the secondary particles, the phosphorus-based flame retardant particles can exist on the surface and internal pores of the metal hydroxide particles.

[0031] When the endothermic material is analyzed using a mass spectrometer according to thermal desorption spectroscopy (TDS), the amount (MS1) of P2 gas desorbed from 80℃ to 1400℃ can be about 200×10 -6 mol / g to about 2500×10 -6 mol / g, about 300×10 -6 mol / g to about 2000×10 -6 mol / g, or about 400×10 -6 mol / g to about 1800×10 -6 mol / g.

[0032] When the endothermic material is analyzed using a mass spectrometer according to thermal desorption spectroscopy (TDS), the amount (MS2) of H2O gas desorbed from 80℃ to 200℃ can be about 50×10 -6 mol / g to about 1000×10 -6 mol / g, about 100×10 -6 mol / g to about 9500×10 -6 mol / g, or about 300×10 -6 mol / g to about 900×10 -6 mol / g.

[0033] The endothermic material can satisfy Equation 1: Equation 1 0.5 ≤ (MS1 / MS2) ≤ 10.0 For example, the endothermic material can satisfy the following Equation 1-1: Equation 1-1 0.5 ≤ (MS1 / MS2) ≤ 5.0 For example, the endothermic material can satisfy the following Equation 1-2: Equation 1-2 0.8 ≤ (MS1 / MS2) ≤ 3.0 When the endothermic material satisfies Equation 1, Equation 1-1, or Equation 1-2, the safety can be improved without deteriorating the performance of the rechargeable lithium battery.

[0034] The endothermic material desirably has a content of Al (aluminum) and P (phosphorus) elements measured during analysis using inductively coupled plasma atomic emission spectrometry (ICP-AES) in the following ranges.

[0035] Based on 100 wt% of the total amount of the endothermic material, the aluminum element can be included in an amount of about 5 wt% to about 30 wt%, or about 5 wt% to about 25 wt%; and the phosphorus element can be included in an amount of about 5 wt% to about 30 wt%, or about 5 wt% to about 25 wt%.

[0036] The content of the aluminum element and the phosphorus element in the endothermic material can be controlled by the type and amount of the metal hydroxide and the flame retardant used in the production of the endothermic material.

[0037] The metal hydroxide can be or include at least one of aluminum hydroxide, boehmite, pseudoboehmite, alumina, kaolinite, and combinations thereof. For example, the metal hydroxide can be or include aluminum hydroxide.

[0038] The D50 particle size of the metal hydroxide can be about 10 nm to about 10 µm, about 50 nm to about 5 µm, or about 0.1 to about 3 µm.

[0039] The phosphorus-based flame retardant includes at least one of phosphoric acid, phosphoric acid ester, phosphonic acid, phosphinic acid, and combinations thereof. For example, the flame retardant can be or include at least one of phosphoric acid, phenyl phosphonate, phenyl phosphinic acid, methyl phosphinic acid, phenyl phosphinic acid, methyl phosphinic acid, phenyl phosphinic acid, and combinations thereof.

[0040] Based on 100 wt% of the total amount of the endothermic material, the metal hydroxide can be included in an amount of about 1 wt% to about 60 wt%, about 5 wt% to about 50 wt%, or about 10 wt% to about 40 wt%; and the phosphorus-based flame retardant can be included in an amount of about 0.1 wt% to about 25 wt%, about 0.5 wt% to about 20 wt%, or about 1 wt% to about 15 wt%.

[0041] The Brunauer, Emmett, and Teller (BET) specific surface area of the endothermic material, calculated from the adsorption isotherm measured by adsorbing nitrogen, can be about 8 m 2 / g to about 150 m 2 / g, about 10 m 2 / g to about 120 m 2 / g, or about 35 m 2 / g to about 100 m 2 / g.

[0042] The BET specific surface area of the endothermic material tends to decrease as the amount of the flame retardant increases when compared to the metal hydroxide, or the reaction time is lengthened when the metal hydroxide and the flame retardant are combined.

[0043] In order to prepare the composite particles including more flame retardant, it is desirable to use a metal hydroxide having as large a specific surface area as possible as a starting material. The specific surface area of the metal hydroxide can be about, for example, 100 m 2 / g to about 500 m 2 / g.

[0044] The D50 particle diameter of the endothermic material can be about 0.05 μm to about 3 μm, about 0.1 μm to about 2 μm, or about 0.5 μm to about 1.5 μm. In addition, the D90 particle diameter of the endothermic material can be about 0.05 μm to about 5 μm, about 2 μm to about 5 μm, or about 2.5 μm to about 5 μm.

[0045] The smaller the D50 particle diameter and the D90 particle diameter of the endothermic material, the thinner and more uniform the thickness of the safety function layer can be made.

[0046] The D50 particle diameter and the D90 particle diameter of the endothermic material can each be controlled by adjusting the preparation conditions of the endothermic material. For example, when the endothermic material is prepared, increasing the temperature or increasing the stirring speed can decrease the D50 particle diameter and the D90 particle diameter of the endothermic material, respectively.

[0047] Method for preparing endothermic material The endothermic material can be manufactured by heating a dispersion of a metal hydroxide and a flame retardant.

[0048] As the solvent of the dispersion, a mixed solvent of water and an organic solvent can be used. As the organic solvent, an alcoholic organic solvent such as ethanol or 2-propanol can be used.

[0049] The heating can be performed at a temperature range of about 40°C to about 100°C, or about 60°C to about 80°C, for about 1 hour to about 48 hours, or about 5 hours to about 30 hours.

[0050] The dispersion can be stirred at a speed of about 50 m / min to about 1000 m / min, or about 200 m / min to about 800 m / min during heating.

[0051] After heating, the endothermic material can be finally obtained by filtering with filter paper.

[0052] The endothermic material can be finally obtained based on whether the P2 gas mass and the H2O gas mass according to thermal desorption spectroscopy satisfy the above ranges, respectively.

[0053] Lithium iron phosphate-based compound The lithium iron phosphate-based compound can be represented by Chemical Formula 1: Chemical Formula 1 Li a Fe 1-x1 M x1 PO4 In Chemical Formula 1, 0.90 ≤ a ≤ 1.8, 0 ≤ x1 ≤ 0.7, and M is Mg, Co, Ni, or a combination thereof.

[0054] For example, the lithium iron phosphate-based compound can be or include LiFePO4.

[0055] Heat-absorbing material First binder The first safety function layer can further include a first binder.

[0056] The first binder can be included in an amount of about 1 wt% to about 30 wt%, about 3 wt% to about 20 wt%, or about 5 wt% to about 10 wt%, based on 100 wt% of the total amount of the first safety function layer.

[0057] The first binder is configured to secure adhesion of components of the first safety function layer to each other, and also to the positive electrode current collector or the second safety function layer, and representative examples can include at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but is not limited thereto.

[0058] Second binder The second safety function layer can further include a second binder.

[0059] The second binder can be included in an amount of about 1 wt% to about 30 wt%, or about 1 wt% to about 20 wt%, based on 100 wt% of the total amount of the second safety function layer.

[0060] The second binder is configured to attach components of the second safety function layer to each other and to the positive electrode current collector or the first safety function layer, and representative examples can include at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, an epoxy resin, nylon, etc., but is not limited thereto.

[0061] Thickness of the first and second safety function layers The total thickness of the first safety function layer and the second safety function layer can be about 0.1 µm to about 3 µm, about 1 µm to about 3 µm, or about 2 µm to about 3 µm.

[0062] The thickness ratio of the first safety function layer to the second safety function layer can be about 10:1 to about 1:10, about 5:1 to about 1:5, or about 5:1 to about 1:1.

[0063] Within the above-described ranges, the cycle life of the rechargeable lithium battery can be improved while reducing the probability of fire and reducing the interfacial resistance.

[0064] Rechargeable lithium battery Some example embodiments include a rechargeable lithium battery including: a positive electrode; a negative electrode; and an electrolyte.

[0065] Since the rechargeable lithium battery according to some example embodiments includes the positive electrode, heat generation and fire can be reduced or suppressed and safety can be ensured even in various situations such as penetration by a sharp object or exposure to high temperatures.

[0066] Hereinafter, a description overlapping the above-described description will be omitted, and the rechargeable lithium battery according to some example embodiments will be described in detail.

[0067] Positive electrode active material The positive electrode active material can be or include a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). For example, one or more types of composite oxides of lithium and a metal including at least one of cobalt, manganese, nickel, and combinations thereof can be used.

[0068] The complex oxide can be or include a lithium transition metal complex oxide, and examples can include at least one of a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free lithium nickel manganese-based oxide, and combinations thereof.

[0069] As an example, a compound represented by any one of the following chemical formulas can be used. 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-c Co 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-gG 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).

[0070] In the above chemical formula, A is Ni, Co, Mn or a combination thereof; X is or includes at least one of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and a combination thereof; D is or includes at least one of O, F, S, P and a combination thereof; G is or includes at least one of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and a combination thereof; and L 1 It is or includes at least one of Mn, Al and combinations thereof.

[0071] For example, the positive electrode active material may include at least one of lithium nickel-based oxide represented by Chemical Formula 11, lithium cobalt-based oxide represented by Chemical Formula 12, lithium iron phosphate-based compound represented by Chemical Formula 13, lithium nickel manganese-based oxide not containing cobalt represented by Chemical Formula 14, and combinations thereof.

[0072] Chemical formula 11 Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In Chemical Formula 11, 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, M 1 and M 2 Each independently is or includes one or more elements including at least one of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is or includes one or more of F, P, and S.

[0073] In Chemical Formula 1, 0.6≤x1≤1, 0≤y1≤0.4, and 0≤z1≤0.4, or 0.8≤x1≤1, 0≤y1≤0.2, and 0≤z1≤0.2.

[0074] Chemical formula 12 Li a2 Co x2 M 3 y2 O 2-b2 Xb2 In Chemical Formula 12, 0.9≤a2≤1.8, 0.7≤x2≤1, 0≤y2≤0.3, 0.9≤x2+y2≤1.1, and 0≤b2≤0.1, M 3 is or includes one or more 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 or includes one or more of F, P, and S.

[0075] Chemical Formula 13 Li a3 Fe x3 M 4 y3 PO 4-b3 X b3 In Chemical Formula 13, 0.9≤a3≤1.8, 0.6≤x3≤1, 0≤y3≤0.4, and 0≤b3≤0.1, M 4 is or includes one or more of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is or includes one or more of F, P, and S.

[0076] Chemical Formula 14 Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4 In Chemical Formula 14, 0.9≤a2≤1.8, 0.8≤x4<1, 0<y4≤0.2, 0≤z4≤0.2, 0.9≤x4+y4+z4≤1.1, and 0≤b4≤0.1, M 5 is or includes one or more of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is or includes one or more of F, P, and S.

[0077] As an example, the positive electrode active material may be or include a high-nickel positive electrode active material having a nickel content of greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol%, and less than or equal to about 99 mol%, based on 100% of the metal other than lithium in the lithium transition metal composite oxide. The high-nickel positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density rechargeable lithium batteries.

[0078] Positive electrode The positive electrode may include: a positive electrode current collector; a safety function layer located on the positive electrode current collector; and a positive electrode active material layer located on the safety function layer.

[0079] The positive electrode active material layer may include a positive electrode active material and may further include a binder and / or a conductive material.

[0080] For example, the positive electrode may further include an additive capable of constituting a sacrificial positive electrode.

[0081] The amount of the positive electrode active material may be about 90 wt % to about 99.5 wt % based on 100 wt % of the positive electrode active material layer, and the amount of each or at least one of the binder and the conductive material may be about 0.5 wt % to about 5 wt % based on 100 wt % of the positive electrode active material layer.

[0082] The binder is configured to attach the positive electrode active material particles to each other and also to attach the positive electrode active material to the current collector. Examples of the binder include, but are not limited to, at least one of 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, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0083] A conductive material is included to provide electrode conductivity. Unless the conductive material causes chemical changes in the battery, any conductive material can be an electrically conductive material. Examples of the conductive material can include or include: carbon-based materials such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials such as at least one of copper, nickel, aluminum, and silver in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0084] The current collector can include Al, but is not limited thereto.

[0085] Negative electrode active material The negative electrode active material can be or include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0086] The material that reversibly intercalates / deintercalates lithium ions can include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon can be or include graphite such as at least one of natural graphite (or artificial graphite) in an amorphous, flaky, sheet, spherical, or fibrous form. The amorphous carbon can be or include soft carbon, hard carbon, meso-phase pitch carbonization products, calcined coke, or the like.

[0087] The lithium metal alloy can include lithium and a metal containing at least one selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0088] The material capable of doping / undoping lithium can be or include a Si-based negative electrode active material or a Sn-based negative electrode active material. The Si-based negative electrode active material can include silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2), Si-Q alloy (wherein Q is or includes at least one of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof). The Sn-based negative electrode active material can include Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0089] The silicon-carbon composite can be or include a composite of silicon and amorphous carbon. According to some example embodiments, the silicon-carbon composite can be in a form in which amorphous carbon is coated on the surface of silicon particles. For example, the silicon-carbon composite can include secondary particles (cores) assembled of primary silicon particles and an amorphous carbon coating (shell) on the surface of the secondary particles. The amorphous carbon can also be between the primary silicon particles, for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed in an amorphous carbon matrix.

[0090] The silicon-carbon composite can further include crystalline carbon. For example, the silicon-carbon composite can include a core including crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core.

[0091] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used in combination with the carbon-based negative electrode active material.

[0092] Negative electrode The negative electrode for a rechargeable lithium battery includes a current collector and a negative electrode mixture layer located on the current collector. The negative electrode mixture layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0093] For example, the negative electrode active mixture layer may include about 90 wt % to about 99 wt % of a negative electrode active material, about 0.5 wt % to about 5 wt % of a binder, and about 0 wt % to about 5 wt % of a conductive material.

[0094] The binder can attach the negative electrode active material particles to each other and also attach the negative electrode active material to the current collector. The binder can include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0095] The non-aqueous binder may include at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and combinations thereof.

[0096] The aqueous binder may be or include at least one of styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0097] When the aqueous binder is a negative electrode binder, the aqueous binder may further include a cellulose compound capable of imparting viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and alkali metal salts thereof. The alkali metal may be or include one or more of Na, K, and Li.

[0098] The dry binder may be or include a polymer material capable of being fiberized, and may be or include, for example, at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, and combinations thereof.

[0099] The electrically conductive material to provide the electrode conductivity can be any electrically conductive material except for the case where the electrically conductive material causes a chemical change of the battery. Examples of the electrically conductive material can be or include at least one of: carbon-based materials such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, and the like; metal-based materials such as at least one of copper, nickel, aluminum, silver, and the like in the form of a metal powder or a metal fiber; electrically conductive polymers such as polyphenylene derivatives; or a mixture thereof.

[0100] The negative electrode current collector can include at least one of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with an electrically conductive metal, and a combination thereof, but is not limited thereto.

[0101] Electrolyte solution The electrolyte for the rechargeable lithium battery includes a non-aqueous organic solvent and a lithium salt.

[0102] The non-aqueous organic solvent constitutes a medium for transporting ions participating in an electrochemical reaction of the battery.

[0103] The non-aqueous organic solvent can be or include at least one of carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, aprotic solvents, and a combination thereof.

[0104] The carbonate-based solvents can include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like. The ester-based solvents can include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, methyl hydroxy valerate, valerolactone, caprolactone, and the like. The ether-based solvents can include at least one of dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyl tetrahydrofuran, 2,5-dimethyl tetrahydrofuran, tetrahydrofuran, and the like. The ketone-based solvents can include cyclohexanone. The alcohol-based solvents can include ethanol, isopropyl alcohol, and the like, and the aprotic solvents can include at least one of nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, or includes a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane or 1,4-dioxolane; sulfolane; and the like.

[0105] The non-aqueous organic solvent can be used alone or as a mixture of two or more.

[0106] In addition, when a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can be used in mixture, and the cyclic carbonate and the chain carbonate can be mixed at a volume ratio of about 1:1 to about 1:9.

[0107] The lithium salt dissolved in the organic solvent supplies lithium ions in the battery, enabling the rechargeable lithium battery to operate substantially, and improving the transport of lithium ions between the positive electrode and the negative electrode. Examples of the lithium salt can include at least one of 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) (wherein x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), lithium difluoro(oxalato)borate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0108] Separator Depending on the type of the battery, the rechargeable lithium battery can further include a separator between the negative electrode and the positive electrode. Examples of suitable separator materials include at least one of polyethylene, polypropylene, polyvinylidene fluoride, and a multilayer such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene triple-layer separator, and a polypropylene / polyethylene / polypropylene triple-layer separator.

[0109] The separator can include a porous substrate and a coating layer including an organic material, an inorganic material, or a combination thereof on one or both surfaces of the porous substrate.

[0110] The porous substrate can be or include a polymeric film formed of (or including) any one of the following polymers or a copolymer or mixture of two or more of them: a polyolefin (including at least one of polyethylene and polypropylene), a polyester (such as polyethylene terephthalate or polybutylene terephthalate), a polyacetal, a polyamide, a polyimide, a polycarbonate, a polyether ketone, a polyaryletherketone, a polyetherimide, a polyamideimide, a polybenzimidazole, a polyether sulfone, a polyphenylene ether, a cyclic olefin copolymer, a polyphenylene sulfide, a polyethylene naphthalate, a glass fiber, Teflon (tetrafluoroethylene), and polytetrafluoroethylene.

[0111] The organic material can include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0112] The inorganic material can include inorganic particles including at least one of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof, but is not limited thereto.

[0113] The organic material and the inorganic material can be mixed in one coating layer, or a coating layer including the organic material and a coating layer including the inorganic material can be stacked.

[0114] Rechargeable lithium battery The rechargeable lithium battery can be classified into a cylindrical, a prismatic, a pouch, or a coin type battery, etc. according to a shape of the battery. Figures 1 to 4 is a schematic diagram illustrating a rechargeable lithium battery according to an example embodiment. Figure 1 is illustrated a cylindrical battery, Figure 2 is illustrated a prismatic battery, Figure 3 and Figure 4 is illustrated a pouch battery. Referring to Figures 1 to 4 The rechargeable lithium battery 100 includes an electrode assembly 40 in which a separator 30 is interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is accommodated. The positive electrode 10, the negative electrode 20, and the separator 30 can be impregnated with an electrolyte (not shown). As shown in Figure 1 The rechargeable lithium battery 100 can include a sealing member 60 that seals the case 50. In addition, in Figure 2 The rechargeable lithium battery 100 can include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in Figure 3 and Figure 4 The rechargeable lithium battery 100 includes Figure 4 the electrode tab 70 shown in Figure 3 the positive electrode tab 71 and the negative electrode tab 72 shown in

[0115] The rechargeable lithium battery according to some example embodiments can be applied to a car, a mobile phone, and / or various types of electrical devices, but the present disclosure is not limited thereto.

[0116] Hereinafter, examples and comparative examples of the present disclosure are described. However, these examples should not be construed as limiting the scope of the disclosure in any sense.

[0117] Preparation Example 1 1.0 g of aluminum hydroxide (D50: 1.2 µm, BET: 212 m2 / g) and 5.0 g of methyl phosphinic acid were dispersed in 50 cc of a solvent prepared by mixing distilled water and ethanol at a volume ratio of 1:1.

[0118] After stirring the dispersion at 300 m / min at 70°C for 24 hours, the solid formed therein was filtered, washed with water and ethanol, and vacuum-dried to obtain the endothermic material.

[0119] Reference Example The endothermic material of Preparation Example 1 was analyzed as follows.

[0120] (1) Desorbed gas mass The amount of desorbed P2 gas (MS1) from 80°C to 1400°C and the amount of desorbed H2O gas (MS2) from 80°C to 200°C of the endothermic material of Preparation Example 1 were measured by using a mass spectrometer (product name: TDS-1200, manufacturer: ESCO Co., Ltd.) according to thermal desorption spectroscopy.

[0121] For example, 1 mg of the endothermic material of Preparation Example 1 was taken as a sample, and the sample was corrected to the actual weight. The sample was placed in a sample pan made of SiC on a sample stage made of quartz. The surface temperature of the sample was increased from 80°C to 1400°C at 60°C / min.

[0122] The mass of the gas desorbed from the sample was measured by using a quadrupole mass spectrometer at a voltage of 1000 V. However, the amount of P2 gas (MS1) was measured as a cumulative value from 80°C to 1400°C, and the amount of H2O gas (MS2) was measured as a cumulative value from 80°C to 200°C. The measurement value was explained by using the mass number [M / z] of H2O as 18.

[0123] The measurement result showed that the MS1 of the endothermic material of Preparation Example 1 was 1195 μmol / g, the MS2 was 558, and the MS1 / MS2 was 2.1.

[0124] (2) Elemental analysis The amount of aluminum element and the amount of phosphorus element of the endothermic material of Preparation Example 1 were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES, product name: Agilent 5110 VDV, manufacturer: Agilent Technologies) based on 100 wt% of the total weight of the endothermic material.

[0125] The measurement result showed that the aluminum element content of the endothermic material of Preparation Example 1 was 17 wt% and the phosphorus element content was 20 wt% based on 100 wt% of the total amount of the endothermic material.

[0126] (3) BET specific surface area The BET specific surface area of the heat storage material of Preparation Example 1 was measured according to JIS K 6217-2 by using a gas adsorption measuring device (product name: BELSORP, manufacturer: MicrotracBEL Co., Ltd.).

[0127] The measurement results show that the heat storage material of Preparation Example 1 has a BET specific surface area of 35 m 2 / g.

[0128] (4) D50 particle diameter and D90 particle diameter The D50 particle diameter at 50% of the particle size distribution and the D90 particle diameter at 90% of the particle size distribution of the heat storage material of Preparation Example 1 were measured according to the laser diffraction method by using a particle size measuring device (product name: MT3300, manufacturer: MicrotracBEL Co., Ltd.) under the following conditions.

[0129] Permeability: permeable Shape: non-spherical Circulation speed: 7 Measurement time: 30 seconds Number of repetitions: 3 Refractive index: a. Heat storage material: 1.65; b. Ethanol solvent: 1.36 As a result of the measurement, the heat storage material of Preparation Example 1 has a D50 particle diameter of 0.8 μm and a D90 particle diameter of 3.5 μm.

[0130] Example 1 (1) Production of positive electrode LiFePO4 (D50: 1.2 μm) and polyvinylidene fluoride as a first binder were mixed at a weight ratio of 92.5:7.5, and then dispersed in N-methylpyrrolidone to prepare a first safety function layer slurry.

[0131] The first safety function layer slurry was coated on a 10-μm-thick Al foil and dried at 110°C to form a first safety function layer.

[0132] The heat storage material of Preparation Example 1 and polyvinylidene fluoride as a second binder were mixed at a weight ratio of 87:13, and then dispersed in N-methylpyrrolidone to prepare a second safety function layer slurry.

[0133] The second safety function layer slurry was coated on the first safety function layer, and then dried at 110°C to form a second safety function layer.

[0134] LiCoO2 as a positive electrode active material, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material were mixed at a weight ratio of 98.5:0.75:0.75, and then dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0135] The positive electrode active material slurry was coated on the second safety function layer, and then dried at 110°C to form a positive electrode active material layer.

[0136] As shown above, the first safety function layer, the second safety function layer, and the positive electrode active material layer were sequentially formed on the Al foil and pressed to obtain a positive electrode.

[0137] Finally, in the obtained positive electrode, the thickness of the first safety function layer was 2.5 μm, the thickness of the second safety function layer was 0.5 μm, and the thickness of the positive electrode active material layer was 40 μm.

[0138] (2) Manufacture of rechargeable lithium battery cell A mixture of artificial graphite and silicon particles as a negative electrode active material, a styrene-butadiene rubber binder, and carboxymethyl cellulose at a weight ratio of 97:1:2 were mixed, and then dispersed in distilled water to prepare a negative electrode active material slurry.

[0139] The negative electrode active material slurry was coated on a 6-μm-thick Cu foil, dried at 100°C, and pressed to manufacture a negative electrode.

[0140] The manufactured positive electrode and negative electrode were assembled with a 10-μm-thick polyethylene separator to manufacture an electrode assembly, the electrode assembly was inserted into a pouch having a width of 5.9 cm, a length of 7.8 cm, and a thickness of 5.4 mm as a battery case, and an electrolyte was injected into the battery case to manufacture a rechargeable lithium battery cell.

[0141] The electrolyte was prepared by dissolving 1.3 M LiPF6 in a mixed solvent in which ethylene carbonate (EC), polypropylene (PP), and propylene carbonate (PC) were mixed at a volume ratio of 1:1:1.

[0142] Example 2 A positive electrode and a rechargeable lithium battery cell were manufactured in the same manner as in Example 1, except that the thickness of the first safety function layer was changed to 2 μm, and the thickness of the second safety function layer was changed to 1 μm.

[0143] Example 3 A positive electrode and a rechargeable lithium battery cell were manufactured in the same manner as in Example 1, except that the thickness of the first safety function layer was changed to 1.5 μm, and the thickness of the second safety function layer was changed to 1.5 μm.

[0144] Example 4 A positive electrode and a rechargeable lithium battery cell were manufactured in the same manner as in Example 1, except that the thickness of the first safety function layer was changed to 1 μm, and the thickness of the second safety function layer was changed to 2 μm.

[0145] Example 5 A positive electrode and a rechargeable lithium battery cell were manufactured in the same manner as in Example 1, except that the thickness of the first safety function layer was changed to 0.5 μm, and the thickness of the second safety function layer was changed to 2.5 μm.

[0146] Example 6 A positive electrode and a rechargeable lithium battery cell were manufactured in the same manner as in Example 2, except that the second safety function layer, the first safety function layer, and the positive electrode active material layer were sequentially formed on the Al foil.

[0147] Comparative Example 1 (1) Manufacture of a positive electrode LiCoO2positive electrode active material, polyvinylidene fluoride binder, and Ketjen black conductive material were mixed in a weight ratio of 98.5:0.75:0.75, and then dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0148] The positive electrode active material slurry was coated on an Al foil, and then dried at 110°C and pressed to obtain a positive electrode.

[0149] In the obtained positive electrode, the thickness of the positive electrode active material layer was 45 μm.

[0150] (2) Manufacture of a rechargeable lithium battery cell A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that the positive electrode was used.

[0151] For reference, the positive electrodes according to Examples 1 to 6 and Comparative Example 1 are summarized in Table 1 below.

[0152] Table 1

[0153] Evaluation Example 1: nail penetration test Ten (10) groups of the rechargeable lithium battery cells of Examples 1 to 6 and Comparative Example 1, each of which was made to have a state of charge (SoC) of 100%, were prepared.

[0154] A nail having a diameter of 3 mm was penetrated into the center portion of the rechargeable lithium battery cell at 150 mm / s. Each of 10 rechargeable lithium battery cells was tested to evaluate the ratio (%) of the rechargeable lithium battery cell which caught fire after being penetrated by the nail, and the results are shown in Table 2 below.

[0155] Evaluation Example 2: Electrode Interface Resistance Measurement For the rechargeable lithium battery cells of Example 1 to Example 6 and Comparative Example 1, the interface resistance of the positive electrode was obtained by a resistance analyzer (Analyzer product name: 46-pin resistance meter, manufacturer: Hioki E.E. Co., Ltd.). The interface resistance of the positive electrode is shown in Table 2 below.

[0156] Evaluation Example 3: Room Temperature Cycle Life and High Temperature Cycle Life Evaluation The rechargeable lithium battery cells of Example 1 to Example 6 and Comparative Example 1 were charged and discharged under the following conditions to evaluate the cycle characteristics, and the results are shown in Table 2 below.

[0157] The cells were cycled 200 times at 25°C with 1.0C charging (CC / CV, 4.47V, cut-off at 0.1C) and 1.0C discharging (CC, cut-off at 2.75V) to calculate the capacity retention according to Equation 2.

[0158] Independently, the cells were cycled 200 times at 45°C with 1.0C (CC / CV, 4.47V, cut-off at 0.1C) charging and 1.0C discharging (CC, cut-off at 2.75V) to calculate the capacity retention according to Equation 2.

[0159] [Equation 2] Capacity retention = (discharge capacity after 200 cycles / discharge capacity after 1 cycle) x 100 Table 2

[0160] Summary Referring to Table 2, the positive electrode according to some example embodiments represented by Example 1 to Example 6 ensures safety by reducing or suppressing the heat generation and ignition of the rechargeable lithium battery cell in various situations such as penetration by a sharp object, exposure to high temperature, etc.

[0161] The positive electrode of Comparative Example 1 does not include a safety function layer, but the positive electrodes of Example 1 to Example 6 include a safety function layer including a first safety function layer including a lithium iron phosphate-based compound and a second safety function layer including a heat-absorbing material.

[0162] For example, the positive electrode of Comparative Example 1 exhibits a low interface resistance due to the absence of a lithium iron phosphate-based compound, and exhibits a 100% ignition probability in the nail penetration test due to the absence of a heat-absorbing material.

[0163] In contrast, the positive electrode of Example 1 to Example 6 exhibited a high interfacial resistance due to the presence of the lithium iron phosphate-based compound and exhibited a 50% or less probability of ignition in the nail penetration test due to the presence of the endothermic material.

[0164] Accordingly, the positive electrode according to some example embodiments represented by Example 1 to Example 6 improves safety by reducing or suppressing heat generation and ignition of the rechargeable lithium battery cell in various situations such as penetration with a sharp object, exposure to high temperature, etc.

[0165] For reference, the higher the interfacial resistance of the positive electrode, the more the safety of the rechargeable lithium battery is improved, but the more the cycle life characteristics are deteriorated due to a trade-off relationship between safety and cycle life characteristics. Accordingly, the thickness ratio of the first safety function layer to the second safety function layer can be appropriately controlled in consideration of the trade-off characteristics.

[0166] For example, the thickness ratio of the first safety function layer to the second safety function layer can be 10:1 to 1:10, 5:1 to 1:5, or 5:1 to 1:1.

[0167] In any of the above ranges, not only is the probability of ignition reduced, but the interfacial resistance is also reduced, improving the cycle life of the rechargeable lithium battery cell.

[0168] While the disclosure has been described in connection with what is presently considered to be the practical example embodiments, it is to be understood that the disclosure is not limited to the disclosed example embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0169] <Description of reference numerals> 100: rechargeable lithium battery 10: positive electrode 11: positive electrode lead tab 12: positive electrode terminal 20: negative electrode 21: negative electrode lead tab 22: negative electrode terminal 30: separator 40: electrode assembly 50: case 60: sealing member 70: electrode tab 71: positive electrode tab 72: negative electrode tab

Claims

1. A positive electrode for a rechargeable lithium battery, the positive electrode comprising: a positive electrode current collector; a safety function layer on the positive electrode current collector; and a positive electrode active material layer on the safety function layer, wherein the safety function layer comprises a first safety function layer including a lithium iron phosphate-based compound and a second safety function layer including an endothermic material. The endothermic material comprises composite particles including a metal hydroxide and a phosphorus-based flame retardant.

2. The positive electrode according to claim 1, wherein, In the endothermic material, 3. The positive electrode of claim 2, wherein, when the endothermic material is analyzed using a mass spectrometer according to thermal desorption spectroscopy (TDS), the endothermic material satisfies Equation 1: The amount of P2 gas desorbed from 80°C to 1400°C MS1 is 200 x 10 -6 mol / g to 2500 x 10 -6 mol / g, and The amount of H2O gas desorbed from 80°C to 200°C MS2 is 50 x 10 -6 mol / g to 1000 x 10 -6 mol / g.

4. The positive electrode of claim 3, wherein, 0.5 ≤ (MS1 / MS2) ≤ 10.0 Equation 1. During analysis using inductively coupled plasma atomic emission spectrometry (ICP-AES), the endothermic material includes 5 wt% to 30 wt% of an aluminum element and 5 wt% to 30 wt% of a phosphorus element, based on 100 wt% in total.

5. The positive electrode of claim 2, wherein, 6.The positive electrode of claim 2, wherein: the metal hydroxide includes at least one of aluminum hydroxide, boehmite, pseudoboehmite, alumina, and kaolinite, and the phosphorus-based flame retardant includes at least one of phosphoric acid, phosphate ester, phosphonic acid, phosphinic acid, and derivatives thereof. The D50 particle diameter of the endothermic material is 0.05 μm to 3 μm.

7. The positive electrode of claim 1, wherein, The heat absorbing material has a BET specific surface area of 8 m 2 / g to 150 m 2 / g.

8. The positive electrode of claim 1, wherein, The lithium iron phosphate-based compound is represented by Chemical Formula 1:

9. The positive electrode of claim 1, wherein, wherein, in Chemical Formula 1, Li a Fe 1-x1 M x1 PO4 formula 1 0 ≤ x1 ≤ 0.7, and 0.90≤a≤1.8， M includes at least one of Mg, Co, and Ni. The first safety function layer further includes a first binder.

10. The positive electrode of claim 1, wherein, The first binder is included in an amount of about 1 wt% to 30 wt%, based on 100 wt% in total of the first safety function layer.

11. The positive electrode of claim 10, wherein, The second safety function layer further includes a second binder.

12. The positive electrode of claim 1, wherein, The second binder is included in an amount of 1 wt% to 30 wt%, based on 100 wt% in total of the second safety function layer.

13. The positive electrode of claim 12, wherein, The total thickness of the first safety function layer and the second safety function layer is 0.1 μm to 3 μm.

14. The positive electrode of claim 1, wherein, The thickness ratio of the first safety function layer to the second safety function layer is 10:1 to 1:

10.

15. The positive electrode of claim 1, wherein, 16.A rechargeable lithium battery, the rechargeable lithium battery comprising: the positive electrode of claim 1; a negative electrode; and an electrolyte. ​ ​

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