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, which is formed on the positive electrode current collector, and which contains over-lithiated oxide particles. The D value represented by formula 1 of the positive electrode may exceed 5.

Description

Technical Field

[0001] The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the positive electrode. More specifically, the present invention relates to a positive electrode for a lithium secondary battery comprising overlithiated oxide particles and a lithium secondary battery including 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 therefore, lithium secondary batteries 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, 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 over-lithiated 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 formula 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 operational stability (eg, lifespan characteristics, etc.) of the overlithiated oxide particles may be low. 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 stability.

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

[0021] (II) Technical solution

[0022] The 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 contains over-lithiated oxide particles represented by the following Chemical Formula 1.

[0023] The D value of the positive electrode represented by the following Formula 1 may exceed 5.

[0024] [Chemical Formula 1]

[0025] Li a [M x Ni y Mn z O b

[0026] 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, 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.

[0027] [Formula 1]

[0028] D = [(I 006 / I 003 ) / C] × 100

[0029] In Formula 1, I 006 is the intensity of the 006 plane peak in the XRD spectrum of the positive electrode active material layer measured after charging and discharging a coin-type half-cell including the positive electrode and a lithium counter electrode twice in a voltage range of 2 V to 4.6 V, I 003 is the intensity of the 003 plane peak in the XRD spectrum, and C is the molar fraction of nickel in the positive electrode active material layer relative to all metal elements except lithium.

[0030] In one embodiment, the D of the positive electrode may be 6 to 12.

[0031] In one embodiment, I 006 / I 003 may be 0.019 to 0.035.

[0032] In one embodiment, C may be 0.25 to 0.45.

[0033] In one embodiment, in the over-lithiated oxide particles, the molar fraction of manganese relative to all elements except lithium and oxygen may be 0.5 to 0.75.

[0034] In one embodiment, in the over-lithiated oxide particles, the molar fraction of cobalt relative to all elements other than lithium and oxygen may be more than 0 and 0.02 or less.

[0035] In one embodiment, the over-lithiated oxide particles may be cobalt-free.

[0036] In one embodiment, in the total weight of the positive electrode active material layer, the content of the over-lithiated oxide particles may be 80% by weight or more.

[0037] A lithium secondary battery according to an exemplary embodiment may include: a positive electrode including 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 over-lithiated oxide particles represented by Chemical Formula 1 below, and D represented by Formula 2 of the positive electrode active material layer A has a value exceeding 5; and a negative electrode disposed opposite to the positive electrode.

[0038] [Chemical Formula 1]

[0039] Li a [M x Ni y Mn z O b

[0040] 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, 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.

[0041] [Formula 2]

[0042] D A =[(I 006 / I 003 ) / C]×100

[0043] In Formula 2, I 006 is the intensity of the 006 plane peak in the XRD spectrum obtained by analyzing the positive electrode active material layer, I 003 is the intensity of the 003 plane peak in the XRD spectrum, and C is the molar fraction of nickel relative to all metal elements other than lithium in the positive electrode active material layer.

[0044] In one embodiment, the upper limit operating voltage of the lithium secondary battery may be 4.5 V or less relative to the redox potential of lithium.

[0045] In one embodiment, the perlithiated oxide particles may comprise Li2MnO3 domains and / or domains derived from the Li2MnO3 domains.

[0046] In one embodiment, the domains derived from the Li2MnO3 domains may include at least one of MnO2, Mn2O4, LiMnO2, LiMn2O4, and Li2Mn2O4.

[0047] (III) Beneficial effects

[0048] 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.

[0049] The lithium secondary battery according to an exemplary embodiment of the present invention includes the positive electrode, thereby can exhibit improved lifespan characteristics. The lithium secondary battery according to some embodiments has an operation upper limit voltage of 4.5V or less, thereby can exhibit further improved lifespan characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a schematic cross-sectional view showing a positive electrode for a lithium secondary battery according to an exemplary embodiment.

[0051] 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. DETAILED DESCRIPTION

[0052] According to an exemplary embodiment of the present invention, there is provided a positive electrode for a lithium secondary battery, the positive electrode including over-lithiated oxide (OLO) particles and having improved capacity and lifespan characteristics.

[0053] In addition, a lithium secondary battery is provided, the lithium secondary battery including the positive electrode.

[0054] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, however, this is merely exemplary and the present invention is not limited to the specific embodiments described exemplarily.

[0055] Positive electrode for lithium secondary battery

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

[0057] Reference Figure 1 The positive electrode 100 for a lithium secondary battery may include a positive electrode current collector 105 and a positive electrode active material layer 110 formed on the positive electrode current collector 105 .

[0058] 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 .

[0059] For example, the positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, copper, or alloys thereof.

[0060] 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.

[0061] According to an exemplary embodiment, the positive active material may include perlithiated oxide particles.

[0062] 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).

[0063] 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.

[0064] For example, the perlithiated oxide particles can be prepared by a co-precipitation method.

[0065] 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 predetermined chemical formula of the perlithiated oxide particles.

[0066] 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.

[0067] In one embodiment, the lithium source may include lithium hydroxide or lithium carbonate. In some embodiments, the lithium source may include lithium hydroxide.

[0068] In one embodiment, the calcination may be performed at 400-1100° C. For example, the calcination may be performed for 2-16 hours.

[0069] In some embodiments, the calcination may include a primary calcination at 200-300°C and a secondary calcination at 700-1100°C.

[0070] 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 formulas 1-1 and 1-2).

[0071] In one embodiment, the activated particles may comprise domains derived from Li2MnO3 domains in the perlithiated oxide particles.

[0072] In some embodiments, the domains derived from the Li2MnO3 domains may include at least one of MnO2, Mn2O4, LiMnO2, LiMn2O4, and Li2Mn2O4.

[0073] 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 the LiMnO2 can reversibly intercalate and deintercalate lithium ions. Therefore, the over-lithiated oxide particles can exhibit high capacity.

[0074] [Reaction formula 1-1]

[0075] (Charging) Li2MnO3→MnO2+2Li + +1 / 2O2+2e -

[0076] [Reaction 1-2]

[0077] (Discharge) MnO2+Li + +e - →LiMnO2

[0078] [Reaction 2]

[0079] (Charging) LiMnO2 → MnO2 + Li + + e -

[0080] (Discharging) MnO2 + Li + + e - → LiMnO2

[0081] 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.

[0082] In an exemplary embodiment, the over-lithiated oxide particles and / or the activated particles may be represented by Chemical Formula 1 below.

[0083] [Chemical Formula 1]

[0084] Li a [M x Ni y Mn z O b

[0085] 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, it may be 0 ≤ x ≤ 0.9, 0 < y ≤ 0.9, 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.

[0086] 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.

[0087] In some embodiments, it may be 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.

[0088] 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.

[0089] In some embodiments, in the perlithiated oxide particles, the molar fraction of manganese relative to all elements except lithium and oxygen may be 0.5 to 0.75, for example, 0.5≤z / (x+y+z)≤0.75.

[0090] In some embodiments, it may be 0.25≤(x+y) / (x+y+z)≤0.5.

[0091] 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.

[0092] In some embodiments, it may be 1.9≤b≤2.1 or 1.95≤b≤2.05.

[0093] 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 (e.g., 2) to obtain the chemical formula of the perlithiated oxide particles and / or the activated particles.

[0094] In one embodiment, the positive active material layer 110 may further include a binder and a conductive material.

[0095] 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).

[0096] In one embodiment, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, carbon nanotubes (CNTs), and metal-based conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, and other perovskite materials.

[0097] 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.

[0098] In addition, due to the unique electrochemical reaction of the Li 2 MnO 3 domains in the over-lithiated oxide particles, the lifespan characteristics of a lithium secondary battery using the over-lithiated oxide particles may be poor.

[0099] However, according to the exemplary embodiment, the D value of the positive electrode 100 represented by the following Formula 1 may exceed 5. Therefore, the lifespan characteristics of the lithium secondary battery may be improved.

[0100] [Formula 1]

[0101] D=(I 006 / I 003 ) / C×100

[0102] In Formula 1, I 006 is the intensity of the 006 face peak in the X-ray diffraction spectrum of the positive electrode active material layer 110 measured after a coin-type half-cell (e.g., a coin-type half-cell having the structure of Example 1) including the positive electrode 100 and the lithium counter electrode is charged and discharged twice in the voltage range of 2V to 4.6V (e.g., after activation), I 003 is the intensity of the 003 face peak in the X-ray diffraction spectrum.

[0103] For example, the conditions of the charge and the discharge may be the same as those of (3) of Example 1 described below.

[0104] In Formula 1, C is the molar fraction of nickel relative to all metal elements except lithium in the positive electrode active material layer 100 measured after activation. For example, C can be measured using inductively coupled plasma (ICP).

[0105] D may represent the disorder degree of the crystal structure of the positive electrode active material layer 100. For example, when D exceeds 5, the probability that the transition metal that moves from the transition metal layer to the lithium layer during charging of the lithium secondary battery returns to the transition metal layer during discharging of the lithium secondary battery may increase. Therefore, the life characteristics of the lithium secondary battery may be improved.

[0106] On the other hand, when D is less than 5, the transition metal that moves from the transition metal layer to the lithium layer during charging of the lithium secondary battery may remain in the lithium layer. Alternatively, the mobile transition metal may be dissolved into the electrolyte. Therefore, the life characteristics of the lithium secondary battery may be reduced.

[0107] In one embodiment, D may be greater than or equal to 6, greater than or equal to 6.5, or greater than or equal to 7. Within the above range, the lifespan characteristics of the lithium secondary battery may be further improved.

[0108] In some embodiments, D may be 10 or less, 9 or less, or 8 or less.

[0109] In one embodiment, I 006 / I 003 It can be from 0.01 to 0.05. In some embodiments, I 006 / I 003 It may be from 0.015 to 0.04 or from 0.019 to 0.035.

[0110] In one embodiment, C may be 0.25 to 0.5, 0.25 to 0.45, 0.3 to 0.45, or 0.4 to 0.45. Within the above range, the capacity and life characteristics of the lithium secondary battery may be further improved.

[0111] Lithium secondary battery

[0112] 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 II'.

[0113] 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 .

[0114] 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.

[0115] In one embodiment, the positive electrode 100 may be the positive electrode for a lithium secondary battery as described above.

[0116] For example, the negative electrode 130 may include a negative electrode collector 125 and a negative electrode active material layer 120 on the negative electrode collector 125. For example, the negative electrode active material layer 120 may be formed on one side or both sides of the negative electrode collector 125.

[0117] For example, the negative electrode active material layer 120 may include a negative electrode active material, the binder, and the conductive material.

[0118] For example, the negative electrode current collector 125 may include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof.

[0119] In one embodiment, the negative electrode active material may be a material that can insert and extract lithium ions. For example, the negative electrode active material may include a lithium alloy, a carbon-based active material, a silicon-based active material, and the like.

[0120] For example, the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0121] For example, the carbon-based active material may include crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.

[0122] For example, the amorphous carbon may include hard carbon, coke, mesocarbon microbeads, mesophase pitch-based carbon fibers, etc.

[0123] For example, the crystalline carbon may include natural graphite, artificial graphite, graphitized coke, graphitized mesocarbon microbeads (MCMB), graphitized mesophase pitch-based carbon fibers (MPCF), etc.

[0124] For example, the silicon-based active material may include Si, SiO x (0 < x < 2), Si / C, SiO / C, Si metal, etc.

[0125] In some embodiments, the area of the negative electrode 130 may be greater than the area of the positive electrode 100.

[0126] 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.

[0127] 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.

[0128] In one embodiment, the negative electrode current collector 125 may include a negative electrode tab 126 that protrudes to one side of the negative electrode current collector 125.

[0129] For example, the negative electrode tab 126 may be integrally formed with the negative electrode current collector 125, or may be electrically connected to the negative electrode current collector 125 by welding or the like. The negative electrode current collector 125 and the negative electrode lead 127 may be electrically connected through the negative electrode tab 126.

[0130] For example, the separator 140 may include a porous polymer membrane prepared from polyolefin-based polymers such as polyethylene, polypropylene, ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-methyl acrylate copolymer, etc. For example, the separator 140 may include a non-woven fabric formed from high melting point glass fibers, polyethylene terephthalate fibers, etc.

[0131] For example, the electrode assembly 150 and the electrolyte may be accommodated together in the soft package case 160 to form a lithium secondary battery.

[0132] In one embodiment, the electrolyte may contain a lithium salt and an organic solvent.

[0133] 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 .

[0134] 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.

[0135] In one embodiment, the lithium secondary battery may refer to the activated lithium secondary battery. Therefore, the positive electrode obtained after disassembling the lithium secondary battery may satisfy the following formula 2.

[0136] [Formula 2]

[0137] D A =[(I 006 / I 003 ) / C]×100

[0138] In formula 2, I 006 is the intensity of the 006 peak in the XRD spectrum of the positive electrode active material layer of the lithium secondary battery, I 003 is the intensity of the 003 plane peak in the XRD spectrum. In addition, C is the molar fraction of nickel relative to all metal elements except lithium in the positive electrode active material layer of the activated lithium secondary battery.

[0139] In one embodiment, D A It may be 6 or more, 6.5 or more, or 7 or more. Within the above range, the life characteristics of the lithium secondary battery can be further improved.

[0140] In some embodiments, D A It may be 10 or less, 9 or less, or 8 or less.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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 + ).

[0145] Hereinafter, the embodiments of the present invention will be further described 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.

[0146] Example 1

[0147] (1) Preparation of perlithiated oxide particles

[0148] 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.

[0149] 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.

[0150] The metal hydroxide particles were dried at 100° C. for 12 hours.

[0151] The metal hydroxide particles and lithium hydroxide are added to a dry mixer, thereby preparing a mixture.

[0152] 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.

[0153] The mixture was charged into a calcining furnace, and the temperature of the calcining furnace was increased to 250° C. at a rate of 2° C. / min and maintained at 250° C. for 3 hours to perform primary calcination.

[0154] 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.

[0155] During the primary calcination and the secondary calcination, oxygen was continuously introduced into the calcination furnace at a flow rate of 10 mL / min.

[0156] After the calcination, the calcined product is naturally cooled to room temperature, and then crushed and classified to prepare perlithiated oxide particles.

[0157] The results of ICP analysis of the over-lithiated oxide particles (normalizing the number of oxygen atoms to 2) confirmed that Li 1.09 Ni 0.38 Mn 0.54 O2.

[0158] (2) Production of initial lithium secondary battery (coin-type half-cell)

[0159] 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.

[0160] The positive electrode slurry was coated on an aluminum foil, dried and rolled to produce a positive electrode. Lithium metal was used as a counter electrode (negative electrode).

[0161] 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.

[0162] 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.

[0163] As the electrolyte solution, an electrolyte solution prepared by dissolving 1M LiPF6 in a mixed solvent of EC / EMC (30:70 v / v) was used.

[0164] (3) Production of lithium secondary batteries (initial activation step of lithium secondary batteries)

[0165] 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).

[0166] The above charging and discharging were repeated twice to activate the superlithiated oxide particles.

[0167] Example 2

[0168] The molar ratio of NiSO4·6H2O and MnSO4·H2O was adjusted to 27.5:72.5 to prepare Li 1.19 Ni 0.22 Mn 0.59 A lithium secondary battery was manufactured in the same manner as in Example 1 except for this.

[0169] Comparative Example 1

[0170] Lithium carbonate was used as a lithium source, and primary calcination was not performed, but secondary calcination was performed for 11 hours to prepare perlithiated oxide particles.

[0171] A lithium secondary battery was manufactured in the same manner as in Example 1 except for the above.

[0172] Comparative Example 2

[0173] 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. No primary calcination was performed, and only a secondary calcination was performed at 1000°C for 11 hours to prepare Li 1.11 Ni 0.34 Mn 0.55 Overlithiated oxide particles with a composition of O2.

[0174] A lithium secondary battery was manufactured in the same manner as in Example 1 except for the above.

[0175] Comparative Example 3

[0176] NiSO4·6H2O, MnSO4·H2O and CoSO4·7H2O were used in a molar ratio of 26.0:71.6:2.4, and lithium carbonate was used as a lithium source. No primary calcination was performed, and only a secondary calcination was performed at 1000°C for 11 hours to prepare a Li 1.19 Ni 0.21 Co 0.02 Mn 0.58 Overlithiated oxide particles with a composition of O2.

[0177] Evaluation Example 1: Evaluation of initial characteristics

[0178] (1) ICP analysis

[0179] The lithium secondary batteries of the examples and comparative examples were disassembled to obtain positive electrodes, and then all positive electrode active material layers were scraped off from the positive electrodes to prepare samples.

[0180] The components of the sample were analyzed using inductively coupled plasma (ICP), and the mole fraction C of Ni relative to all metal elements (ie, Ni and Mn, or Ni, Co, and Mn) in the sample was calculated.

[0181] (2) XRD analysis

[0182] The lithium secondary batteries of the examples and comparative examples were disassembled to obtain positive electrodes, and then the positive electrode active material layers were subjected to X-ray diffraction (XRD) analysis.

[0183] The XRD analysis equipment and conditions are listed in Table 1 below.

[0184] [Table 1]

[0185]

[0186] In the obtained XRD spectrum, the intensity of the 006 plane peak (observed at 2θ of 36° to 38°) and the intensity of the 003 plane peak (observed at 2θ of 17° to 19°) were calculated.

[0187] (3) Calculation of the degree of disorder (D) of the crystal structure

[0188] The C and I calculated in (1) and (2) of Evaluation Example 1 were 006 and I 003 Substitute the value into the following formula 1 to calculate the D value.

[0189] [Formula 1]

[0190] D=[I (006) / I (003) ] / C×100

[0191] Evaluation Example 2: Evaluation of Life Characteristics

[0192] 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) at 45°C.

[0193] Repeat the above charging and discharging 100 times, and measure the second discharge capacity DC2 and the 100th discharge capacity DC 100 .

[0194] The capacity retention rate was calculated according to the following formula.

[0195] Capacity retention rate (%) = DC 100 / DC2×100(%)

[0196] [Table 2]

[0197]

[0198] Referring to Table 2, the lithium secondary battery of the embodiment exhibits improved lifespan characteristics compared to the lithium secondary battery of the comparative example.

[0199] 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: 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 contains over-lithiated oxide particles represented by the following Chemical Formula 1, The D value represented by the following Formula 1 of the positive electrode for the lithium secondary battery exceeds 5, [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, 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] D=[(I 006 / I 003 ) / C]×100 In formula 1, I 006 is the intensity of the 006 peak in the XRD spectrum of the positive electrode active material layer measured after the coin-type half-cell including the positive electrode and the lithium counter electrode is charged and discharged twice in the voltage range of 2V to 4.6V, I 003 is the intensity of the 003 plane peak in the XRD spectrum, and C is the molar fraction of nickel in the positive electrode active material layer relative to all metal elements except lithium.

2. The positive electrode for a lithium secondary battery according to claim 1, wherein D is from 6 to 12.

3. The positive electrode for a lithium secondary battery according to claim 1, wherein I 006 / I 003 is from 0.019 to 0.

035.

4. The positive electrode for a lithium secondary battery according to claim 1, wherein C is from 0.25 to 0.

45.

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

75.

6. The positive electrode for a lithium secondary battery according to claim 1, wherein In the over-lithiated oxide particles, the molar fraction of cobalt relative to all elements except lithium and oxygen is more than 0 and 0.02 or less.

7. The positive electrode for a lithium secondary battery according to claim 1, wherein The over-lithiated oxide particles do not contain cobalt.

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

9. A lithium secondary battery, comprising: The positive electrode comprises a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is formed on the positive electrode current collector, the positive electrode active material layer comprises perlithiated oxide particles represented by the following chemical formula 1, and the positive electrode active material layer has a D represented by the following formula 2 A The value is greater than 5; and A negative electrode disposed opposite to the positive electrode, [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, 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 2] D A =[(I 006 / I 003 ) / C]×100 In formula 2, I 006 is the intensity of the 006 peak in the XRD spectrum of the positive electrode active material layer, I 003 is the intensity of the 003 plane peak in the XRD spectrum, and C is the molar fraction of nickel in the positive electrode active material layer relative to all metal elements except lithium.

10. The lithium secondary battery according to claim 9, wherein: The upper operating voltage of the lithium secondary battery is 4.5 V or less with respect to the redox potential of lithium.

11. The lithium secondary battery according to claim 9, wherein The over-lithiated oxide particles contain at least one of Li2MnO3 domains and domains derived from the Li2MnO3 domains.

12. The lithium secondary battery according to claim 11, wherein The domains derived from the Li2MnO3 domains contain at least one selected from MnO2, Mn2O4, LiMnO2, LiMn2O4 and Li2Mn2O4.

Images