Positive electrode for lithium secondary battery and lithium secondary battery comprising same

Abstract

A positive electrode for a lithium secondary battery according to an exemplary embodiment may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes over-lithiated oxide particles. The electrochemically active surface area of the positive electrode may be 0.5 m2 / g to 2.5 m2 / g.

Description

Technical Field

[0001] The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery comprising the positive electrode, and more particularly to a positive electrode for a lithium secondary battery comprising overlithiated oxide particles and a lithium secondary battery comprising the positive electrode. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged, and are widely used as a power source for portable electronic devices such as mobile phones and laptops.

[0003] Lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and lightness, and thus are being actively developed and applied.

[0004] Lithium secondary batteries can store electrical energy by using the difference in chemical potential when lithium ions are intercalated and deintercalated between the positive and negative electrodes. Therefore, lithium secondary batteries can use substances that can reversibly intercalate and deintercalate lithium ions as positive and negative electrode active materials.

[0005] For example, as the positive electrode active material, lithium metal oxide particles having a layered crystal structure of ABO2 (e.g., lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), lithium nickel cobalt manganese oxide (NCM), lithium nickel aluminum manganese oxide (NCA), etc.) are used. The lithium metal oxide particles can achieve a reversible capacity of about 100 mAh / g to 230 mAh / g.

[0006] In addition, as lithium secondary batteries are applied to electric vehicles (EVs) and the like, lithium metal oxide particles having a higher capacity than the lithium metal oxide particles are being researched and developed.

[0007] It is known that the perlithiated oxide particles have a structure in which lithium is embedded in the transition metal site of the lithium metal oxide particles having an ABO2 layered crystal structure. Therefore, the perlithiated oxide particles can be represented as Li a M b O2 (M is a transition metal such as Mn, Ni, Co, etc., and 1.8≤a+b≤2.2 and a / b≥1.05).

[0008] According to the XRD analysis results of the perlithiated oxide particles, the perlithiated oxide particles may contain Li2MnO3 domains (C2 / m space group) and LiMO2 domains (R3m space group, M is Mn, Ni, Co, etc.). Therefore, the perlithiated oxide particles may also be expressed as xLi2MnO3·(1-x)LiMO2(0.05 <x<1)。

[0009] The overlithiated oxide particles can exhibit a reversible capacity of more than 250 mAh / g through the electrochemical reaction of Li2MnO3.

[0010] For example, although Li2MnO3 is electrochemically inactive, as shown in the following reaction formula 1, Li2MnO3 can be activated by an activation process (e.g., a lithium secondary battery using over-lithiated oxide particles at 4.4 V (vs. Li / Li + ) is charged and discharged above) and converted into LiMnO2. As shown in the following reaction formula 2, the LiMnO2 can reversibly intercalate and deintercalate lithium ions. Therefore, the over-lithiated oxide particles can exhibit a high reversible capacity based on the LiMO2 domain and the Li2MnO3 domain.

[0011] [Reaction 1]

[0012] (Charging) Li2MnO3→MnO2+2Li + +1 / 2O2+2e -

[0013] (Discharge) MnO2+Li + +e - →LiMnO2

[0014] [Reaction 2]

[0015] (Charging) LiMnO2→MnO2+Li + +e -

[0016] (Discharge) MnO2+Li + +e - →LiMnO2

[0017] However, the overlithiated oxide particles have poor operating reliability (eg, life characteristics, etc.). Summary of the invention

[0018] 1. Technical issues to be resolved

[0019] A technical problem of the present invention is to provide a positive electrode for a lithium secondary battery having improved capacity and operating reliability.

[0020] A technical problem of the present invention is to provide a lithium secondary battery with improved capacity and operating reliability.

[0021] (II) Technical solution

[0022] A positive electrode for a lithium secondary battery according to an exemplary embodiment may include a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, the positive electrode active material including perlithiated oxide particles represented by the following chemical formula 1. The electrochemically active surface area of ​​the positive electrode represented by the following formula 1 may be 0.5 m 2 / g to 2.5m 2 / g.

[0023] [Chemical formula 1]

[0024] Li a [M x Ni y Mn z ]O b

[0025] In Chemical Formula 1, M may be at least one of Co, Mg, V, Ti, Al, Fe, Ru, Zr, W, Sn, Nb, Mo, Cu, Zn, Cr, Ga, V, and Bi, and may be 0≤x≤0.9, 0≤y≤0.9, x+y>0, 0.1≤z≤0.9, 1.8≤a+x+y+z≤2.2, 1.05≤a / (x+y+z)≤1.95, and 1.8≤b≤2.2.

[0026] [Formula 1]

[0027] Electrochemically active surface area (m 2 / g)=C(F) / [W(g)×{0.2(F / m 2 )}]

[0028] In Formula 1, C is the capacitance of one side of the positive electrode measured by analyzing a two-electrode symmetrical battery manufactured using two of the positive electrodes by cyclic voltammetry, and W is the weight of the positive electrode active material contained in one positive electrode in the two-electrode symmetrical battery.

[0029] In one embodiment, the positive electrode may have a 1.1 m 2 / g to 1.8m 2 / g of the electrochemically active surface area.

[0030] In one embodiment, the XRD peak intensity ratio of the positive electrode represented by the following Formula 2 may be 4% or more.

[0031] [Formula 2]

[0032] XRD peak intensity ratio (%) = 100 × I (110) / [I (110) + I (003)]

[0033] In Formula 2, I(110) is the maximum height of the (110) peak in the XRD spectrum of the positive electrode active material layer, and I(003) is the maximum height of the (003) peak in the XRD spectrum.

[0034] In one embodiment, the content of the over-lithiated oxide particles may be 80 wt % or more in the total weight of the positive electrode active material layer.

[0035] In one embodiment, the positive electrode active material layer may have a density of 2.5 g / cubic centimeter (cc) to 3.8 g / cc.

[0036] In one embodiment, in the perlithiated oxide particles, the molar fraction of manganese relative to all elements except lithium and oxygen may be from 0.5 to 0.75.

[0037] In one embodiment, in the perlithiated oxide particles, the molar fraction of cobalt relative to all elements except lithium and oxygen may be from 0 to 0.02.

[0038] In one embodiment, the overlithiated oxide particles may have a form of secondary particles in which a plurality of primary particles are aggregated, and the plurality of primary particles may include plate-like particles having an aspect ratio of 3 to 9.

[0039] In one embodiment, in a scanning electron microscope (SEM) image measuring a cross section of the perlithiated oxide particle, a ratio of a total area of ​​the flaky particles to an area of ​​the perlithiated oxide particle may be 0.8 or more.

[0040] In one embodiment, the perlithiated oxide particles may include perlithiated oxide particles satisfying Formula 3.

[0041] [Formula 3]

[0042] P h / P f <0.2

[0043] In formula 3, P f P is the total area of ​​pores present in the perlithiated oxide particle measured in a scanning electron microscope (SEM) image of a cross section of the perlithiated oxide particle. h When the radius of the perlithiated oxide particle is defined as R, it is the total area of ​​pores existing in the region from the surface to a thickness of 0.5R of the perlithiated oxide particle.

[0044] In one embodiment, the perlithiated oxide particles may comprise Li2MnO3 domains and / or domains derived from the Li2MnO3 domains.

[0045] In one embodiment, the domains derived from the Li2MnO3 domains may include at least one of MnO2, Mn2O4, LiMnO2, LiMn2O4, and Li2Mn2O4.

[0046] In one embodiment, the positive electrode may satisfy Formula 4.

[0047] [Formula 4]

[0048] (Rct2 / Rct1)×100≤220%

[0049] In Formula 4, when a half-cell is manufactured using the positive electrode and the lithium counter electrode, Rct1 is the charge transfer resistance value of the positive electrode measured by electrochemical impedance spectroscopy after the half-cell is repeatedly charged and discharged at 1C for 100 times in a voltage range of 2V to 4.3V at 45°C. Rct2 is the charge transfer resistance value of the positive electrode measured by electrochemical impedance spectroscopy after the half-cell is repeatedly charged and discharged at 1C for 100 times in a voltage range of 2V to 4.5V at 45°C.

[0050] A lithium secondary battery according to an exemplary embodiment may include: the positive electrode; and a negative electrode disposed opposite to the positive electrode.

[0051] In one embodiment, the operating upper limit voltage of the lithium secondary battery may be 4.5 V or less relative to the redox potential of lithium.

[0052] (III) Beneficial effects

[0053] The positive electrode for a lithium secondary battery according to an exemplary embodiment of the present invention includes overlithiated oxide particles, thereby can exhibit high capacity. In addition, the positive electrode for a lithium secondary battery satisfies the following Formula 1, thereby can exhibit improved life characteristics.

[0054] A positive electrode for a lithium secondary battery according to some embodiments includes overlithiated oxide particles having a prescribed morphology, and thus may have improved power characteristics.

[0055] The lithium secondary battery according to the exemplary embodiment includes the positive electrode, and thus may have improved lifespan characteristics and power characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is a schematic cross-sectional view of a positive electrode for a lithium secondary battery according to an exemplary embodiment.

[0057] Figure 2 and Figure 3 1 and 2 are respectively a schematic plan view and a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment.

[0058] Figure 4 , Figure 6 , Figure 8 and Fig.10 The images are respectively obtained by measuring the surfaces of the perlithiated oxide particles of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 using a scanning electron microscope (SEM).

[0059] Figure 5 , Figure 7 , Fig. 9 and Fig.11 These are images of cross sections of perlithiated oxide particles of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 measured using a scanning electron microscope (SEM). DETAILED DESCRIPTION

[0060] According to an exemplary embodiment of the present invention, there is provided a positive electrode for a lithium secondary battery, the positive electrode comprising over-lithiated oxide particles (OLO) and having improved capacity, life characteristics, power characteristics, and the like.

[0061] In addition, a lithium secondary battery is provided, the lithium secondary battery including the positive electrode.

[0062] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, but these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described exemplarily.

[0063] Positive electrode for lithium secondary battery

[0064] Figure 1 is a schematic cross-sectional view showing a positive electrode for a lithium secondary battery according to an exemplary embodiment.

[0065] Reference Figure 1 The positive electrode 100 for a lithium secondary battery may include a positive electrode collector 105 and a positive electrode active material layer 110 formed on the positive electrode collector 105 .

[0066] For example, the positive electrode active material layer 110 may be formed on one surface or both surfaces of the positive electrode current collector 105 .

[0067] For example, the positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, copper, or alloys thereof.

[0068] The positive electrode active material layer 110 may include a positive electrode active material that can reversibly intercalate and deintercalate lithium ions. For example, the positive electrode active material may include lithium metal oxide particles.

[0069] According to an exemplary embodiment, the positive active material may include overlithiated oxide particles.

[0070] In one embodiment, the perlithiated oxide particles may comprise Li2MnO3 domains (C2 / m space group) and Li a M b O c Domain (R3m space group, M is at least one of Ni, Mn, Co, Mg, V, Ti, Al, Fe, Ru, Zr, W, Sn, Nb, Mo, Cu, Zn, Cr, Ga, V and Bi, and 1.8≤a+b≤2.2, 0.9≤a / b<1.05 and 1.9≤c≤2.1).

[0071] In some embodiments, in the perlithiated oxide particles, the molar ratio of the Li2MnO3 domains to the LiMO2 domains may be expressed as w:1-w, and w may be 0.05 to 0.7 or 0.1 to 0.7.

[0072] For example, the perlithiated oxide particles can be prepared by a co-precipitation method.

[0073] For example, a plurality of metal salts, chelating agents (e.g., ammonia, ammonium carbonate, etc.) and coprecipitating agents (e.g., sodium hydroxide, sodium carbonate, etc.) may be mixed and subjected to a coprecipitation reaction to prepare metal hydroxide particles. For example, the molar ratio between the plurality of metal salts may be adjusted according to the chemical formula of the predetermined perlithiated oxide particles.

[0074] For example, the metal hydroxide particles and the lithium source may be mixed so that the ratio of the mole number of the lithium source to the mole number of the metal hydroxide particles is 1.05 to 1.95, 1.1 to 1.95, 1.15 to 1.95, or 1.2 to 1.95, and calcined to prepare the perlithiated oxide particles.

[0075] In one embodiment, the lithium source may include lithium hydroxide or lithium carbonate. In some embodiments, the lithium source may include lithium hydroxide.

[0076] In one embodiment, the calcination may be performed at 400-1100° C. For example, the calcination may be performed for 2-16 hours.

[0077] In some embodiments, the calcination may include a primary calcination at 200-300°C and a secondary calcination at 700-1100°C.

[0078] For example, the overlithiated oxide particles can be charged to a voltage of 4.4 V (vs. Li / Li +) or above (e.g., 4.4 V to 4.8 V) to activate the perlithiated oxide particles (see the following reaction formula 1-1). Alternatively, the lithium secondary battery containing the perlithiated oxide particles can be activated by heating the lithium secondary battery containing the perlithiated oxide particles at 4.4 V (relative to Li / Li + ) or above to activate the overlithiated oxide particles (see the following reaction formula 1-1 and reaction formula 1-2).

[0079] In one embodiment, the activated particles may comprise domains derived from Li2MnO3 domains in the perlithiated oxide particles.

[0080] In some embodiments, the domains derived from the Li2MnO3 domains may include at least one of MnO2, Mn2O4, LiMnO2, LiMn2O4, and Li2Mn2O4.

[0081] For example, as shown in the following reaction formula 1-1 and the following reaction formula 1-2, at least a portion of Li2MnO3 in the over-lithiated oxide particles can be converted into MnO2 and LiMnO2 by the activation. As shown in the following reaction formula 2, the MnO2 and LiMnO2 can reversibly intercalate and deintercalate lithium ions. Therefore, the over-lithiated oxide particles can exhibit high capacity.

[0082] [Reaction formula 1-1]

[0083] (Charging) Li2MnO3→MnO2+2Li + +1 / 2O2+2e -

[0084] [Reaction 1-2]

[0085] (Discharge) MnO2+Li + +e - →LiMnO2

[0086] [Reaction 2]

[0087] (Charging) LiMnO2→MnO2+Li + +e -

[0088] (Discharge) MnO2+Li + +e - →LiMnO2

[0089] In some embodiments, the LiMnO2 in the activated particles may further react and be converted into Mn2O4, LiMn2O4 or Li2Mn2O4.

[0090] In some embodiments, the activated particles may comprise the Li a M b O c domains, Li2MnO3 domains, and / or domains derived from the Li2MnO3 domains.

[0091] In an exemplary embodiment, the over-lithiated oxide particles and / or the activated particles may be represented by Chemical Formula 1 below.

[0092] [Chemical Formula 1]

[0093] Li a [M x Ni y Mn z O b

[0094] In Chemical Formula 1, M may be at least one of Co, Mg, V, Ti, Al, Fe, Ru, Zr, W, Sn, Nb, Mo, Cu, Zn, Cr, Ga, V, and Bi.

[0095] And, 0≤x≤0.9, 0≤y≤0.9 (where x + y>0), 0.1≤z≤0.9, 1.8≤a + x + y + z≤2.2, 1.05≤a / (x + y + z)≤1.95, and 1.8≤b≤2.2.

[0096] In some embodiments, it may be 0<x≤0.9, 0.05≤x≤0.9, 0.1≤x≤0.9, 0<x≤0.8, 0.05≤x≤0.8, or 0.1≤x≤0.8.

[0097] In some embodiments, it may be 0<y≤0.9, 0.05≤y≤0.9, 0.1≤y≤0.9, 0<y≤0.8, 0.05≤y≤0.8, or 0.1≤y≤0.8.

[0098] In some embodiments, it may be 1.1≤a / (x + y + z)≤1.95, 1.15≤a / (x + y + z)≤1.95, 1.2≤a / (x + y + z)≤1.95, or 1.3≤a / (x + y + z)≤1.95.

[0099] In some embodiments, in the over-lithiated oxide particles, the molar fraction of manganese relative to all elements other than lithium and oxygen may be 0.5 to 0.75. For example, it may be 0.5≤z / (x + y + z)≤0.75.

[0100] In some embodiments, it may be 0.25≤(x + y) / (x + y + z)≤0.5.

[0101] In some embodiments, in the perlithiated oxide particles, the mole fraction of cobalt relative to all elements except lithium and oxygen may be 0 to 0.02. In some embodiments, the perlithiated oxide particles may be free of cobalt.

[0102] In some embodiments, it may be 1.9≤b≤2.1 or 1.95≤b≤2.05.

[0103] For example, the composition of the perlithiated oxide particles and the activated particles can be confirmed by inductively coupled plasma (ICP). For example, the perlithiated oxide particles and / or the activated particles can be analyzed by ICP, and the number of oxygen atoms can be normalized to 1.8-2.2 (preferably, 2) to obtain the chemical formula of the perlithiated oxide particles and / or the activated particles.

[0104] In one embodiment, the positive active material layer 110 may further include a binder and a conductive material.

[0105] In one embodiment, the adhesive may include organic adhesives such as polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, and water-based adhesives such as styrene-butadiene rubber (SBR). In some embodiments, the adhesive may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0106] In one embodiment, the conductive material may include carbon-based conductive materials such as graphite, carbon nanotube (CNT), carbon black, graphene, etc.; metal-based conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3 and other perovskite materials.

[0107] In one embodiment, the content of the over-lithiated oxide particles may be 80 wt % or more, 85 wt % or more, or 90 wt % or more of the total weight of the positive electrode active material layer 110. In some embodiments, the content of the over-lithiated oxide particles may be 98 wt % or less, or 95 wt % or less of the total weight of the positive electrode active material layer 110.

[0108] In one embodiment, the loading amount of the positive electrode active material layer 110 may be 5-28 mg / cm 2 , 7-25mg / cm 2 , 8-20mg / cm 2 or 9-15 mg / cm 2 .

[0109] In one embodiment, the density of the positive active material layer 110 may be 2.5-3.8 g / cm 3 , 2.6-3.7 g / cm 3 , or 2.7-3.6 g / cm 3 .

[0110] In addition, due to the unique electrochemical reaction of the Li 2 MnO 3 domains in the overlithiated oxide particles, a lithium secondary battery using the overlithiated oxide particles may have poor lifespan characteristics.

[0111] In addition, in the case of a lithium secondary battery using the over-lithiated oxide particles, a relatively high voltage operating range can be provided compared to a lithium secondary battery using conventional lithium metal oxide particles. At high voltage, the side reaction of the over-lithiated oxide particles and the electrolyte may be aggravated, and thus the life characteristics of the lithium secondary battery may be deteriorated.

[0112] In an exemplary embodiment, the electrochemical active surface area of ​​the positive electrode 100 represented by the following formula 1 may be 0.5-2.5 m 2 Therefore, the lifespan characteristics of the lithium secondary battery can be improved.

[0113] [Formula 1]

[0114] Electrochemically active surface area (m 2 / g)=C(F) / [W(g)×{0.2(F / m 2 )}]

[0115] In Formula 1, C is the electrochemical double layer capacitance (EDLC) value of one side (one) positive electrode measured by cyclic voltammetry analysis of a two-electrode symmetry cell made using two positive electrodes 100. W is the weight of the positive electrode active material contained in one positive electrode in the two-electrode symmetry cell.

[0116] For example, the electrochemically active surface area of ​​the positive electrode 100 can be measured according to Evaluation Example 2 described below.

[0117] Unlike the specific surface area (BET), the electrochemically active surface area can substantially obtain information related to the electrochemical reaction on the electrode surface and near the electrode surface. Therefore, by adjusting the electrochemically active surface area, the reduction in the life characteristics of the lithium secondary battery caused by the over-lithiated oxide particles can be effectively prevented.

[0118] For example, when the electrochemically active surface area of ​​the positive electrode 100 is less than 0.5 m 2 / g, the power characteristics of the lithium secondary battery may be excessively reduced. In addition, when the electrochemically active surface area of ​​the positive electrode 100 exceeds 2.5 m 2 / g, the life characteristics of the lithium secondary battery may be deteriorated.

[0119] In one embodiment, the electrochemically active surface area of ​​the positive electrode 100 may be 0.5-2.4 m 2 / g, 0.6-2.3m 2 / g, 0.7-2.2m 2 / g, 0.8-2.1m 2 / g, 0.9-2m 2 / g, 1-1.9m 2 / g or 1.1-1.8m 2 Within the above range, the life characteristics of the lithium secondary battery can be further improved.

[0120] In one embodiment, the XRD peak intensity ratio of the positive electrode 100 represented by the following Formula 2 may be 4% or more or 5% or more. In some embodiments, the XRD peak intensity ratio may be 10% or less, 9% or less, 8% or less, or 7% or less.

[0121] [Formula 2]

[0122] XRD peak intensity ratio (%) = 100 × I (110) / [I (110) + I (003)]

[0123] In Formula 2, I(110) is the maximum height of the (110) peak in the XRD spectrum of the positive electrode active material layer, and I(003) is the maximum height of the (003) peak.

[0124] When the positive electrode 100 satisfies the XRD peak intensity ratio within the above range, the lifespan characteristics and power performance of the lithium secondary battery may be improved at the same time.

[0125] In one embodiment, the perlithiated oxide particles (and the activated particles) may be in the form of secondary particles formed by aggregation of a plurality of primary particles.

[0126] In some embodiments, the plurality of primary particles may include flaky particles having an aspect ratio of 2.5 to 12, 3 to 9, or 4 to 7. For example, the aspect ratio may be defined as the length of the long side (or long axis) of the flaky particle divided by the thickness. For example, the aspect ratio may be measured in a scanning electron microscope (SEM) image measuring the over-lithiated oxide particles. For example, when the electrochemically active surface area of ​​the positive electrode is reduced, the power characteristics of the lithium secondary battery may be reduced. However, by adjusting the morphology of the primary particles to the flaky form, the reduction in power performance can be prevented.

[0127] In some embodiments, the particle size D of the perlithiated oxide particles (the secondary particles) is 50 The particle size D 50 It may be a particle size at 50% of the volume particle size distribution, and can be measured using a laser diffraction method.

[0128] In some embodiments, the perlithiated oxide particles (the secondary particles) may have a sphericity of 0.7 or more, 0.8 or more, or 0.9 or more.

[0129] In some embodiments, in a scanning electron microscope (SEM) image measuring the surface of the over-lithiated oxide particles, the length of the long side of the flaky particles may be 0.1-3 μm, 0.3-2.5 μm, 0.5-2 μm, 0.75-1.5 μm or 0.8-1.2 μm. In addition, the thickness of the flaky particles may be 100-200 nm. Within the above range, the power performance of the lithium secondary battery can be further improved.

[0130] In some embodiments, in a scanning electron microscope (SEM) image measuring a cross-section of the perlithiated oxide particle, a ratio of the total area of ​​the flaky particles to the area of ​​the perlithiated oxide particle (excluding pore portions) may be 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more.

[0131] In one embodiment, the perlithiated oxide particles may include perlithiated oxide particles satisfying the following Formula 3. Therefore, the lifespan characteristics of the lithium secondary battery may be further improved.

[0132] [Formula 3]

[0133] P h / P f <0.2

[0134] In formula 3, P f P is the total area of ​​pores present in the perlithiated oxide particle measured in a scanning electron microscope (SEM) image of a cross section of the perlithiated oxide particle. hWhen the radius of the perlithiated oxide particle is defined as R, it is the total area of ​​pores existing in the region from the surface to a thickness of 0.5R of the perlithiated oxide particle.

[0135] In some embodiments, P h / P f It may be less than 0.15, less than 0.1, or less than 0.05. In some embodiments, P h / P f It may be 0.01 or more or 0.02 or more.

[0136] In one embodiment, the positive electrode 100 may satisfy Formula 4 below.

[0137] [Formula 4]

[0138] (Rct2 / Rct1)×100≤220%

[0139] In Formula 4, when a half-cell is manufactured using the positive electrode and the lithium counter electrode, Rct1 is the charge transfer resistance value of the positive electrode measured by electrochemical impedance spectroscopy after the half-cell is repeatedly charged and discharged at 1C for 100 times in a voltage range of 2V to 4.3V at 45°C. Rct2 is the charge transfer resistance value of the positive electrode measured by electrochemical impedance spectroscopy after the half-cell is repeatedly charged and discharged at 1C for 100 times in a voltage range of 2V to 4.5V at 45°C.

[0140] In some embodiments, (Rct2 / Rct1)×100 may be 200% or less, 180% or less, 150% or less, or 130% or less.

[0141] Lithium secondary battery

[0142] Figure 2 is a schematic plan view showing a lithium secondary battery according to an exemplary embodiment. Figure 3 It is along Figure 2 Schematic cross-sectional view of a lithium secondary battery taken along line I-I'.

[0143] Reference Figure 2 and Figure 3 The lithium secondary battery may include an electrode assembly 150 and a case 160 accommodating the electrode assembly 150 .

[0144] The electrode assembly 150 may include a positive electrode 100 and a negative electrode 130 disposed opposite to the positive electrode 100. In one embodiment, the electrode assembly 150 may further include a separator 140 interposed between the positive electrode 100 and the negative electrode 130.

[0145] In one embodiment, the positive electrode 100 may be the positive electrode for the above-described lithium secondary battery.

[0146] For example, the negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 on the negative electrode current collector 125. For example, the negative electrode active material layer 120 may be formed on one or both surfaces of the negative electrode current collector 125.

[0147] For example, the negative electrode active material layer 120 may contain a negative electrode active material, the binder, and the conductive material.

[0148] For example, the negative electrode current collector 125 may include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof.

[0149] In one embodiment, the negative electrode active material may be a material that allows lithium ions to be intercalated and deintercalated. For example, the negative electrode active material may include a lithium alloy, a carbon-based active material, a silicon-based active material, etc.

[0150] For example, the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0151] For example, the carbon-based active material may include crystalline carbon, amorphous carbon, a carbon composite, carbon fiber, etc.

[0152] For example, the amorphous carbon may include hard carbon, coke, mesocarbon microbeads, mesophase pitch-based carbon fiber, etc.

[0153] For example, the crystalline carbon may include natural graphite, artificial graphite, graphitized coke, graphitized mesocarbon microbeads (MCMB), graphitized mesophase pitch-based carbon fiber (MPCF), etc.

[0154] For example, the silicon-based active material may include Si, SiO x (0 < x < 2), Si / C, SiO / C, Si Metal, etc.

[0155] In some embodiments, the area of the negative electrode 130 may be larger than the area of the positive electrode 100.

[0156] In one embodiment, the positive electrode current collector 105 may include a positive electrode tab 106 that protrudes to one side of the positive electrode current collector 105.

[0157] For example, the positive electrode tab 106 may be integrally formed with the positive electrode current collector 105, or may be electrically connected to the positive electrode current collector 105 by welding or the like. The positive electrode current collector 105 and the positive electrode lead 107 may be electrically connected through the positive electrode tab 106.

[0158] In one embodiment, the negative electrode collector 125 may include a negative electrode tab 126 protruding to one side of the negative electrode collector 125 .

[0159] For example, the negative electrode tab 126 may be formed integrally with the negative electrode collector 125 , or may be electrically connected to the negative electrode collector 125 by welding, etc. The negative electrode collector 125 and the negative electrode lead 127 may be electrically connected through the negative electrode tab 126 .

[0160] For example, the separator 140 may include a porous polymer film made of a polyolefin-based polymer such as polyethylene, polypropylene, ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-methacrylate copolymer, etc. For example, the separator 140 may include a non-woven fabric formed of high melting point glass fiber, polyethylene terephthalate fiber, etc.

[0161] For example, the electrode assembly 150 and the electrolyte may be housed together in the case 160 of the pouch to form a lithium secondary battery.

[0162] In one embodiment, the electrolyte may include a lithium salt and an organic solvent.

[0163] In one embodiment, the lithium salt may include Li + X - For example, X - It can be F - , Cl - Br - ,I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2- 、SCN - and (CF3CF2SO2)2N - Any of .

[0164] In one embodiment, the organic solvent may include carbonate-based solvents such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); ester-based solvents such as methyl propionate, ethyl propionate, ethyl acetate, propyl acetate, butyl acetate, butyrolactone, caprolactone, and valerolactone; ether-based solvents such as dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), and tetrahydrofuran (THF); alcohol-based solvents such as ethanol and isopropanol; ketone-based solvents such as cyclohexanone; aprotic solvents such as amide-based solvents (e.g., dimethylformamide), dioxolane-based solvents (e.g., 1,3-dioxolane), sulfolane-based solvents, and nitrile-based solvents, etc.

[0165] In one embodiment, the upper limit voltage of the lithium secondary battery can be relative to the redox potential of lithium (relative to Li / Li + The “operating upper limit voltage” refers to the upper limit voltage of the lithium secondary battery during actual operation (i.e., during actual use), which can be distinguished from the activation voltage of the activation process in the manufacturing process of the lithium secondary battery.

[0166] In some embodiments, the upper limit voltage of the lithium secondary battery can be relative to the redox potential of lithium (relative to Li / Li + ) below 4.5V. In some embodiments, the operating upper limit voltage may be 4.3V to 4.5V. Within the above range, the life characteristics of the lithium secondary battery can be further improved.

[0167] In one embodiment, the lower limit voltage of the lithium secondary battery can be relative to the redox potential of lithium (relative to Li / Li + ) is above 1.8V, above 1.9V or above 2.0V. In some embodiments, the lower limit operating voltage may be 1.8V to 2.2V.

[0168] In some embodiments, the operating voltage range (i.e., operating voltage interval) of the lithium secondary battery may be 2V (relative to Li / Li + ) to 4.5V (relative to Li / Li + ).

[0169] The embodiments of the present invention are further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only used to illustrate the present invention and are not used to limit the scope of the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and the technical concept, which is obvious to those skilled in the art, and it is natural that such variations and modifications belong to the scope of the claims.

[0170] Example 1

[0171] (1) Preparation of perlithiated oxide particles

[0172] Distilled water from which dissolved oxygen had been removed was added to the closed reactor, and NiSO4·6H2O and MnSO4·H2O were further added at a molar ratio of 41:59.

[0173] NaOH (precipitant) and NH 4 OH (chelating agent) were further added to the reactor, and a coprecipitation reaction was performed for 60 hours, thereby preparing metal hydroxide particles.

[0174] The metal hydroxide particles were dried at 100° C. for 12 hours.

[0175] The metal hydroxide particles and lithium hydroxide are added to a dry mixer, thereby preparing a mixture.

[0176] The mixing ratio of the metal hydroxide particles and the lithium hydroxide is adjusted so that the prepared lithium metal oxide particles satisfy the composition according to the following ICP analysis.

[0177] The mixture was put into a calcining furnace, the temperature of the calcining furnace was increased to 250° C. at 2° C. / min, and maintained at 250° C. for 3 hours to perform primary calcination.

[0178] After the primary calcination, the temperature of the calcination furnace was increased to 850° C. at a rate of 2° C. / min and maintained at 850° C. for 8 hours to perform secondary calcination.

[0179] During the primary calcination and the secondary calcination, oxygen was continuously introduced into the calcination furnace at 10 mL / min.

[0180] After the calcination, the calcined product is naturally cooled to room temperature, and then crushed and classified to prepare perlithiated oxide particles.

[0181] The results of ICP analysis of the overlithiated oxide particles (normalizing the number of oxygen atoms to 2) confirmed that Li 1.09 Ni 0.38 Mn 0.54 O2.

[0182] (2) Manufacturing of initial lithium secondary battery (coin-type half-cell)

[0183] The perlithiated oxide particles, carbon black, and polyvinylidene fluoride (PVDF) were dispersed in N-methyl-2-pyrrolidone (NMP) at a weight ratio of 92:5:3 to prepare a positive electrode slurry.

[0184] The positive electrode slurry was coated on an aluminum foil, dried and rolled to manufacture a positive electrode having a positive electrode active material layer. When manufacturing the positive electrode, the loading amount of the positive electrode active material layer was adjusted to 11 mg / cm 2 , and the density of the positive electrode active material layer was adjusted to 2.8 g / cm3. As the counter electrode (negative electrode), lithium metal was used.

[0185] The positive electrode and the negative electrode are cut into circular shapes with diameters of Φ14 and Φ16, respectively, and stacked, and a separator (polyethylene (PE), with a thickness of 13 µm) cut into Φ19 is arranged between the positive electrode and the negative electrode to form an electrode assembly.

[0186] The electrode assembly was housed in a coin-type battery case (2016 specification), and an electrolyte was injected into the coin-type battery case, thereby manufacturing an initial lithium secondary battery.

[0187] As the electrolyte solution, an electrolyte solution prepared by dissolving 1 M LiPF6 in a mixed solvent of EC / EMC (30:70 v / v) was used.

[0188] (3) Production of lithium secondary batteries (initial lithium secondary battery activation step)

[0189] At 25° C., the initial lithium secondary battery was subjected to CC / CV charging (0.1 C constant current, CC interval cut-off condition: 4.6 V, CV interval cut-off condition: 0.05 C) and CC discharging (0.1 C constant current, 2.0 V cut-off).

[0190] The above charging and discharging were repeated twice to activate the superlithiated oxide particles.

[0191] Example 2

[0192] The molar ratio of NiSO4·6H2O to MnSO4·H2O was adjusted to 27.5:72.5 to prepare the overlithiated oxide particles (Li 1.19 Ni 0.22 Mn 0.59 O2).

[0193] A lithium secondary battery was manufactured in the same manner as in Example 1 except for the above.

[0194] Comparative Example 1

[0195] Lithium carbonate was used as the lithium source.

[0196] The primary calcination was not performed, and only the secondary calcination was performed for 11 hours, thereby preparing perlithiated oxide particles.

[0197] A lithium secondary battery was manufactured in the same manner as in Example 1 except for the above.

[0198] Comparative Example 2

[0199] The added molar ratio of NiSO4·6H2O and MnSO4·H2O was adjusted to 38.1:61.9, and lithium carbonate was used as the lithium source.

[0200] Instead of performing the primary calcination, the secondary calcination was performed at 1000°C for 11 hours to prepare the over-lithiated oxide particles (Li 1.11 Ni 0.34 Mn 0.55 O2).

[0201] A lithium secondary battery was manufactured in the same manner as in Example 1 except for the above.

[0202] Evaluation Example 1: Measurement of morphology

[0203] (1) Morphology of primary particles

[0204] The surfaces and cross sections of the perlithiated oxide particles of Examples and Comparative Examples were observed using a scanning electron microscope (SEM).

[0205] Figure 4 , Figure 6 , Figure 8 and Fig.10 The SEM images of the surfaces of the perlithiated oxide particles of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were measured respectively. Figure 5 , Figure 7 , Fig. 9 and Fig.11 The SEM images of the cross sections of the perlithiated oxide particles of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were measured respectively.

[0206] Reference Figure 4 and Figure 6 The perlithiated oxide particles of Examples 1 and 2 are in the form of secondary particles formed by aggregation of flaky primary particles. Figure 8 and Fig.10 The perlithiated oxide particles of Comparative Examples 1 and 2 have the form of secondary particles formed by aggregation of circular polygonal primary particles.

[0207] In the above SEM surface image, three primary particles were randomly selected from one perlithiated oxide particle, the aspect ratios of the selected primary particles were measured, and the average of the measured aspect ratios was calculated. When measuring the aspect ratio, in the case of the flaky primary particles, the length / thickness of the long side was measured, and in the case of the circular polygonal primary particles, the length of the major axis / the length of the minor axis was measured.

[0208] (2) Evaluation of primary particle density

[0209] In the SEM cross-sectional image, it is confirmed whether perlithiated oxide particles satisfying the following formula 3 are observed.

[0210] When particles satisfying the following formula 3 were observed, it was marked as ○, and when particles satisfying the following formula 3 were not observed, it was marked as ×.

[0211] [Formula 3]

[0212] P h / P f <0.2

[0213] In formula 3, P f P is the total area of ​​pores present in the perlithiated oxide particle in a SEM cross-sectional image (e.g., a cross-sectional image through the center of the particle) of the perlithiated oxide particle. h When the radius of the perlithiated oxide particle is defined as R, it is the total area of ​​pores existing in the region from the surface to a thickness of 0.5R of the perlithiated oxide particle.

[0214] The radius R is calculated as the average of the major radius and the minor radius of the perlithiated oxide particle in the above SEM cross-sectional image.

[0215] Evaluation Example 2: Measurement of the electrochemically active surface area of ​​the positive electrode

[0216] 1) Fabrication of dual-electrode symmetric battery

[0217] Prepare two lithium secondary batteries of Example 1. Disassemble the two lithium secondary batteries to obtain two positive electrodes.

[0218] A separator (polypropylene (PP), 14 μm thick, Celgard, PP1410) cut into Φ19 was placed between the two positive electrodes to form an electrode assembly.

[0219] The electrode assembly was housed in a coin-type battery case (2016 specification), and an electrolyte was injected into the coin-type battery case, thereby manufacturing a symmetrical battery.

[0220] As the electrolyte, a 1 M LiPF6 solution (solvent: EC / EMC / DEC=25 / 45 / 30 v / v%) was used.

[0221] 2) Measurement of electrochemical double layer capacitance of the positive electrode

[0222] The symmetrical battery was analyzed by cyclic voltammetry to measure the electrochemical double layer capacitance (EDLC, hereinafter referred to as capacitance) of the positive electrode.

[0223] The specific measurement method is as follows.

[0224] i) The symmetrical cell was connected to a potentiostat (VMP-3 from Biologic).

[0225] A voltage is applied to the symmetrical battery so that the potential is reciprocated in a voltage interval where no Faraday current flows (i.e., a non-Faraday voltage interval; -0.10 V to +0.10 V) (initial potential→upper limit potential→initial potential→lower limit potential→initial potential), and a cyclic voltammogram (CV curve) is measured. When measuring the CV curve, the voltage scan rate is adjusted to 10 mV / sec.

[0226] ii) Obtaining the response peak current from the CV curve.

[0227] iii) The voltage scan rate was changed to 20 mV / sec, 30 mV / sec, 40 mV / sec and 50 mV / sec, and i) and ii) were further performed.

[0228] iv) Setting the voltage scan rate as the x-axis and the peak current response according to the voltage scan rate as the y-axis to draw a linear graph. Obtain a slope value from the linear graph (linear regression analysis). The slope value is the total capacitance C of the two positive electrodes in the symmetrical battery. tot .

[0229] v) In a symmetrical battery, C=2C tot (C is the capacitance of the positive electrode on one side) is established, so by tot Substitute the above formula to calculate the capacitance C of one positive electrode.

[0230] 3) Calculation of the electrochemically active surface area of ​​the positive electrode

[0231] The capacitance of a platinum (Pt) electrode (i.e. 0.2 F / m 2) was used as a reference, and the electrochemical active surface area (EASA) of the positive electrode of Example 1 was calculated according to the following formula 1.

[0232] [Formula 1]

[0233] Electrochemically active surface area (m 2 / g)=C(F) / [W(g)×{0.2(F / m 2 )}]

[0234] In Formula 1, C is the capacitance value of the positive electrode on one side calculated in 2) above, and W is the total weight of the positive electrode active material contained in one positive electrode in the symmetrical battery.

[0235] The active surface areas of the positive electrodes of Example 2, Comparative Example 1, and Comparative Example 2 were measured by the same method as described above.

[0236] Evaluation Example 3: X-ray diffraction (XRD) analysis

[0237] The lithium secondary batteries of the examples and comparative examples were disassembled to obtain positive electrodes, and the positive electrode active material layer of the positive electrodes was analyzed using XRD. The XRD spectra were analyzed to calculate the XRD peak intensity ratio represented by the following formula 2.

[0238] The XRD analysis equipment and conditions are described in Table 1 below.

[0239] [Table 1]

[0240]

[0241] [Formula 2]

[0242] XRD peak intensity ratio (%) = 100 × I (110) / [I (110) + I (003)]

[0243] In Formula 2, I(110) is the maximum height of the (110) peak in the XRD spectrum, and I(003) is the maximum height of the (003) peak in the XRD spectrum.

[0244] Evaluation Example 4: Evaluation of the surface resistance (charge transfer resistance, Rct) of the positive electrode

[0245] Two lithium secondary batteries of Example 1 (hereinafter, referred to as a first battery and a second battery, respectively) were prepared.

[0246] At 45° C., the first battery was charged and discharged at 1C in a voltage range of 2.0 V to 4.3 V. The above charging and discharging were repeated 100 times.

[0247] The electrochemical impedance of the first battery was measured using a potentiostat (Biologic, VMP-3) to confirm the surface resistance Rct1 of the positive electrode.

[0248] At 45° C., the second battery was charged and discharged at 1C in a voltage range of 2.0 V to 4.5 V. The above charging and discharging were repeated 100 times.

[0249] The electrochemical impedance of the second battery was measured to confirm the surface resistance Rct2 of the positive electrode.

[0250] According to the following formula 4, the Rct ratio (RR, %) of the voltage range cycle from 2.0 V to 4.5 V and the voltage range cycle from 2.0 V to 4.3 V is calculated.

[0251] [Formula 4]

[0252] RR(%)=(Rct2 / Rct1)×100

[0253] The surface resistance of the positive electrodes of Example 2, Comparative Example 1 and Comparative Example 2 was measured by the same method as described above, and the RR value of Formula 4 was calculated.

[0254] Evaluation Example 5: Evaluation of Life Characteristics (45°C)

[0255] The lithium secondary batteries of the examples and comparative examples were subjected to CC / CV charging (1 C constant current, 4.5 V and 0.05 C cut-off) and CC discharging (1 C constant current, 2.0 V cut-off).

[0256] The above charging and discharging were repeated 100 times, and the second discharge capacity D2 and the 100th discharge capacity D 100 .

[0257] The capacity retention rate was calculated according to the following formula.

[0258] Capacity retention rate (%) = D 100 / D2×100(%)

[0259] [Table 2]

[0260]

[0261] Referring to Table 2, the lithium secondary battery of the example exhibits improved lifespan characteristics compared to the lithium secondary battery of the comparative example.

[0262] Furthermore, the lithium secondary battery of the example exhibited a low surface resistance (charge transfer resistance) of the positive electrode even at a high voltage, compared with the lithium secondary battery of the comparative example.

[0263] The above-described contents are merely examples of applying the principles of the present invention, and other configurations may be further included without departing from the scope of the present invention.

Claims

1. A positive electrode for a lithium secondary battery, comprising: Positive electrode current collector; as well as A positive electrode active material layer, the positive electrode active material layer is formed on the positive electrode current collector, the positive electrode active material layer contains a positive electrode active material, the positive electrode active material contains perlithiated oxide particles represented by Chemical Formula 1, The electrochemically active surface area of ​​the positive electrode for the lithium secondary battery represented by Formula 1 is 0.5 m 2 / g to 2.5m 2 / g, [Chemical formula 1] Li a [M x Ni y Mr z ]O b In Chemical Formula 1, M is at least one of Co, Mg, V, Ti, Al, Fe, Ru, Zr, W, Sn, Nb, Mo, Cu, Zn, Cr, Ga, V, and Bi, and 0≤x≤0.9, 0≤y≤0.9, x+y>0, 0.1≤z≤0.9, 1.8≤a+x+y+z≤2.2, 1.05≤a / (x+y+z)≤1.95, and 1.8≤b≤2.2, [Formula 1] Electrochemically active surface area (m 2 / g)=C(F) / [W(g)×{0.2(F / m 2 )}] In Formula 1, C is the capacitance of one side of the positive electrode measured by analyzing a two-electrode symmetrical battery manufactured using two of the positive electrodes by cyclic voltammetry, and W is the weight of the positive electrode active material contained in one positive electrode in the two-electrode symmetrical battery.

2. The positive electrode for a lithium secondary battery according to claim 1, wherein The positive electrode for a lithium secondary battery has a 1.1 m 2 / g to 1.8m 2 / g of the electrochemically active surface area.

3. The positive electrode for a lithium secondary battery according to claim 1, wherein The XRD peak intensity ratio of the positive electrode for the lithium secondary battery represented by Formula 2 is 4% or more, [Formula 2] XRD peak intensity ratio (%) = 100 × I (110) / [I (110) + I (003)] In Formula 2, I(110) is the maximum height of the (110) peak in the XRD spectrum of the positive electrode active material layer, and I(003) is the maximum height of the (003) peak in the XRD spectrum.

4. The positive electrode for a lithium secondary battery according to claim 1, wherein The content of the over-lithiated oxide particles is 80 wt % or more in the total weight of the positive electrode active material layer.

5. The positive electrode for a lithium secondary battery according to claim 1, wherein The density of the positive electrode active material layer is 2.5 g / cubic centimeter to 3.8 g / cubic centimeter.

6. The positive electrode for a lithium secondary battery according to claim 1, wherein In the perlithiated oxide particles, the molar fraction of manganese relative to all elements except lithium and oxygen is from 0.5 to 0.

75.

7. The positive electrode for a lithium secondary battery according to claim 1, wherein In the perlithiated oxide particles, the molar fraction of cobalt relative to all elements except lithium and oxygen is from 0 to 0.

02.

8. The positive electrode for a lithium secondary battery according to claim 1, wherein The perlithiated oxide particles have a secondary particle form in which a plurality of primary particles are aggregated, and the plurality of primary particles include plate-like particles having an aspect ratio of 3 to 9.

9. The positive electrode for a lithium secondary battery according to claim 8, wherein In a scanning electron microscope (SEM) image measuring a cross section of the perlithiated oxide particle, a ratio of a total area of ​​the flaky particles to an area of ​​the perlithiated oxide particle is 0.8 or more.

10. The positive electrode for a lithium secondary battery according to claim 8, wherein The perlithiated oxide particles include perlithiated oxide particles satisfying Formula 3, [Formula 3] P h / P f <0.2 In formula 3, P f To measure the total area of ​​pores present in the perlithiated oxide particle in a scanning electron microscope (SEM) image of a cross section of the perlithiated oxide particle, P h When the radius of the perlithiated oxide particle is defined as R, it is the total area of ​​pores existing in the region from the surface to a thickness of 0.5R of the perlithiated oxide particle.

11. The positive electrode for a lithium secondary battery according to claim 1, wherein The overlithiated oxide particles include at least one of Li2MnO3 domains and domains derived from the Li2MnO3 domains.

12. The positive electrode for a lithium secondary battery according to claim 11, wherein The domain derived from the Li2MnO3 domain includes at least one selected from MnO2, Mn2O4, LiMnO2, LiMn2O4 and Li2Mn2O4.

13. The positive electrode for a lithium secondary battery according to claim 1, wherein The positive electrode for the lithium secondary battery satisfies Formula 4, [Formula 4] (Rct2 / Rct1)×100≤220% In Formula 4, when a half-cell is manufactured using the positive electrode and the lithium counter electrode, Rct1 is the charge transfer resistance value of the positive electrode measured by electrochemical impedance spectroscopy after the half-cell is repeatedly charged and discharged at 1C for 100 times in a voltage range of 2V to 4.3V at 45°C, Rct2 is the charge transfer resistance value of the positive electrode measured by electrochemical impedance spectroscopy after the half-cell is subjected to 100 cycles of 1C charging and 1C discharging in the voltage range of 2V to 4.5V at 45°C.

14. A lithium secondary battery comprising: The positive electrode according to claim 1; as well as A negative electrode is arranged opposite to the positive electrode.

15. The lithium secondary battery according to claim 14, wherein: The upper limit voltage of the lithium secondary battery is 4.5 V or less relative to the oxidation-reduction potential of lithium.

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