Lithium secondary battery and method for operating same

Abstract

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, the positive electrode active material layer being formed on the positive electrode current collector, and the positive electrode active material layer including positive electrode active material particles; and the negative electrode is arranged opposite to the positive electrode. The positive electrode active material particles may include particles in which over-lithiated oxide particles are activated, and a coating material that is formed on at least a portion of a surface of the activated particles, and that contains a coating element. The upper operating limit voltage of the lithium secondary battery may be 4.5 V or less relative to the oxidation-reduction potential of lithium.

Description

Technical Field

[0001] The present invention relates to a lithium secondary battery and a method for operating the lithium secondary battery. More specifically, the present invention relates to a lithium secondary battery comprising a perlithiated oxide as a positive electrode active material and a method for operating the lithium secondary battery. 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 iron phosphate (LFP), 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 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 Summary of the invention

[0017] 1. Technical issues to be resolved

[0018] A technical problem of the present invention is to provide a lithium secondary battery having high capacity and improved operating stability.

[0019] Another technical problem of the present invention is to provide a method for operating a lithium secondary battery with improved stability.

[0020] (II) Technical solution

[0021] 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, the positive electrode active material layer being formed on the positive electrode current collector and the positive electrode active material layer containing positive electrode active material particles; and a negative electrode disposed opposite to the positive electrode. The positive electrode active material particles may include perlithiated oxide particles represented by Chemical Formula 1 and a coating material, the coating material being formed on at least a portion of the surface of the perlithiated oxide particles, and the coating material containing a coating element. The upper operating limit voltage of the lithium secondary battery may be 4.5 V or less relative to the redox potential of lithium.

[0022] [Chemical formula 1]

[0023] Li a [M x Ni y Mn z ]O b

[0024] 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.

[0025] In one embodiment, the D value of the lithium secondary battery represented by Formula 1 may be greater than 0 and less than 0.31.

[0026] [Formula 1]

[0027] D = I (Mn 3+ ) / [I(Mn 3+ )+I(Mn 4+ )]

[0028] In Formula 1, I(Mn 3+ ) is the Mn in the XPS analysis spectrum when the lithium secondary battery is charged and discharged 100 times in the voltage range of 2.0 V to 4.5 V at 45° C. and disassembled, and the positive electrode active material layer is analyzed by X-ray photoelectron spectroscopy (XPS). 3+ Peak area; I(Mn 4+ ) is Mn in the XPS analysis spectrum 4+ The area of ​​the peak.

[0029] In one embodiment, the manganese content of the perlithiated oxide particles may be 50-75 mol % of all elements except lithium and oxygen.

[0030] In one embodiment, the content of cobalt in the perlithiated oxide particles may be less than 2 mol % of all elements except lithium and oxygen.

[0031] In one embodiment, the perlithiated oxide particles may comprise Li2MnO3 domains and / or domains derived from the Li2MnO3 domains.

[0032] In one embodiment, the domain derived from the Li2MnO3 domain may include at least one of MnO2, Mn2O4, LiMnO2, LiMn2O4 and Li2Mn2O4.

[0033] In one embodiment, the coating element may include at least one of B, Al, W, Zr, Ti, Mg, and Co.

[0034] In one embodiment, the content of the coating element in the positive electrode active material particles may be 500-8000 ppm based on the total weight of all elements except lithium and oxygen.

[0035] 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.

[0036] In one embodiment, the operating voltage of the lithium secondary battery may range from 2.0 V to 4.5 V relative to the redox potential of lithium.

[0037] According to the working method of the lithium secondary battery of the exemplary embodiment, a lithium secondary battery including a positive electrode and a negative electrode can be prepared, the positive electrode including positive electrode active material particles, the positive electrode active material particles including perlithiated oxide particles represented by Chemical Formula 1 and a coating material, the coating material is formed on at least a portion of the surface of the perlithiated oxide particles, and the coating material contains a coating element. The lithium secondary battery can be charged and discharged only in a voltage range of 4.5V or less relative to the redox potential of lithium.

[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, 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.

[0041] In one embodiment, the preparing the lithium secondary battery may include charging and discharging the lithium secondary battery at a voltage greater than 4.5 V relative to the oxidation-reduction potential of lithium 1 to 10 times.

[0042] (III) Beneficial effects

[0043] The lithium secondary battery according to the exemplary embodiment includes an over-lithiated oxide, thereby having a high capacity, and has a prescribed upper limit voltage of operation, thereby suppressing voltage decay.

[0044] According to the operating method of the lithium secondary battery of the exemplary embodiment, voltage decay of the lithium secondary battery caused by over-lithiated oxide may be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 and Figure 2 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.

[0046] Figure 3 is a schematic flowchart illustrating an operating method of a lithium secondary battery according to an exemplary embodiment. DETAILED DESCRIPTION

[0047] According to an exemplary embodiment of the present invention, a lithium secondary battery having improved operation reliability even if including over-lithiated oxide particles (OLO) may be provided.

[0048] In addition, a method for operating a lithium secondary battery can be provided, which can improve the operating reliability of the lithium secondary battery using the overlithiated oxide particles.

[0049] Hereinafter, a positive electrode for a lithium secondary battery and a lithium secondary battery according to an exemplary embodiment of the present invention will be described in more detail with reference to the accompanying drawings. However, the drawings and embodiments are merely exemplary, and the present invention is not limited to the drawings and embodiments.

[0050] Figure 1 and Figure 21 and 2 are respectively a schematic plan view and a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. Figure 2 It is along Figure 1 A cross-sectional view taken along line I-I'.

[0051] Reference Figure 1 and Figure 2 The lithium secondary battery may include an electrode assembly 150 and a case 160 accommodating the electrode assembly 150 .

[0052] The electrode assembly 150 may include a positive electrode 100 and a negative electrode 130 disposed opposite to the positive electrode 100 .

[0053] In one embodiment, the electrode assembly 150 may include a plurality of positive electrodes and a plurality of negative electrodes that are alternately and repeatedly disposed.

[0054] In one embodiment, the electrode assembly 150 may further include a separator 140 interposed between the positive electrode 100 and the negative electrode 130 .

[0055] For example, the positive electrode 100 may include a positive electrode collector 105 and a positive electrode active material layer 110 on the positive electrode collector 105. For example, the positive electrode active material layer 110 may be formed on one side or both sides of the positive electrode collector 105.

[0056] For example, the positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, copper, or alloys thereof.

[0057] The positive electrode active material layer 110 may include positive electrode active material particles that can reversibly intercalate and deintercalate lithium ions. For example, the positive electrode active material particles may include lithium metal oxide particles.

[0058] In an exemplary embodiment, the positive active material particles may include perlithiated oxide particles.

[0059] 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).

[0060] 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.

[0061] For example, the perlithiated oxide particles can be prepared by a co-precipitation method.

[0062] 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 a predetermined chemical formula.

[0063] 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.

[0064] In one embodiment, the lithium source may include lithium hydroxide or lithium carbonate. In some embodiments, the lithium source may include lithium hydroxide.

[0065] In one embodiment, the calcination may be performed at 400-1100° C. For example, the calcination may be performed for 2-16 hours.

[0066] In some embodiments, the calcination may include a primary calcination at 200-300° C. and a secondary calcination at 700-1100° C. In this case, the electrochemically active surface area of ​​the over-lithiated oxide particles may be reduced. Therefore, the voltage decay of the lithium secondary battery described below may be further suppressed.

[0067] In some embodiments, the primary calcination may be performed for 1 to 6 hours, and the secondary calcination may be performed for 2 to 16 hours.

[0068] 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 initial lithium secondary battery containing the perlithiated oxide particles may be activated by heating the initial 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).

[0069] In one embodiment, the activated particles may comprise domains derived from Li2MnO3 domains in the perlithiated oxide particles.

[0070] In some embodiments, the domain derived from the Li2MnO3 domain may include at least one of MnO2, Mn2O4, LiMnO2, LiMn2O4, and Li2Mn2O4.

[0071] 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 perlithiated 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.

[0072] [Reaction formula 1-1]

[0073] (Charging) Li2MnO3→MnO2+2Li + +1 / 2O2+2e -

[0074] [Reaction 1-2]

[0075] (Discharge) MnO2+Li + +e - →LiMnO2

[0076] [Reaction 2]

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

[0078] (Discharge) MnO2+Li + +e - →LiMnO2

[0079] In some embodiments, the LiMnO2 in the activated particles may further react and be converted into Mn2O4, LiMn2O4 or Li2Mn2O4.

[0080] In some embodiments, the activated particles may include the Li a M b O c domains, Li2MnO3 domains and / or domains derived from said Li2MnO3 domains.

[0081] In an exemplary embodiment, the perlithiated oxide particles and / or the activated particles may be represented by Chemical Formula 1 below.

[0082] [Chemical formula 1]

[0083] Li a [M x Ni y Mn z ]Ob

[0084] In Chemical Formula 1, M can be at least one of Co, Mg, V, Ti, Al, Fe, Ru, Zr, W, Sn, Nb, Mo, Cu, Zn, Cr, Ga, V, and Bi.

[0085] And, it can be 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.

[0086] In some embodiments, it can 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 can 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.

[0088] In some embodiments, it can 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 over-lithiated oxide particles, the molar fraction of manganese relative to all elements other than lithium and oxygen can be 0.5 to 0.75. For example, it can be 0.5 ≤ z / (x + y + z) ≤ 0.75.

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

[0091] In some embodiments, in the over-lithiated oxide particles, the molar fraction of cobalt relative to all elements other than lithium and oxygen can be 0 to 0.02. In some embodiments, the over-lithiated oxide particles can be cobalt-free.

[0092] In some embodiments, it can 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 addition, a lithium secondary battery using the over-lithiated oxide particles as a positive electrode active material may experience voltage decay during operation, and thus the electrochemical performance of the lithium secondary battery may be deteriorated.

[0095] In one embodiment, the positive electrode active material particles may further include a coating material, the coating material is formed on at least a portion of the surface of the overlithiated oxide particles, and the coating material contains a coating element. In this case, the upper limit voltage of the lithium secondary battery can be adjusted, thereby suppressing the voltage decay of the lithium secondary battery.

[0096] In some embodiments, the coating material may form a coating having a sea-type shape. Alternatively, the coating material may form a coating having an island-type shape.

[0097] In one embodiment, the coating elements may include metal elements and / or metalloid elements.

[0098] In some embodiments, the coating element may include B, Al, W, Zr, Ti, Mg, Co, etc. In some embodiments, the coating element may include B.

[0099] In one embodiment, the content of the coating element in the positive electrode active material particles can be 500-8000ppm, 1000-8000ppm or 1500-8000ppm of the total weight of all elements except lithium and oxygen. Within the above range, the reduction of the initial capacity and the increase of the resistance of the lithium secondary battery can be further prevented, and the voltage decay of the lithium secondary battery can be further suppressed.

[0100] For example, the coating material can be formed by a dry coating method or a wet coating method. For example, the perlithiated oxide particles and the coating source can be dry mixed or wet mixed and heat treated (e.g., calcined or dried) to form the coating material on the surface of the perlithiated oxide particles.

[0101] For example, the coating source may contain B, Al, W, Zr, Ti, Mg, Co, etc., and coating sources known in the technical field may be used.

[0102] In some embodiments, the drying temperature or calcination temperature during the coating may be 200-450° C. In this case, the coating material may be concentrated on the surface of the over-lithiated oxide particles without diffusing into the interior of the over-lithiated oxide particles. Therefore, the voltage decay of the lithium secondary battery may be further suppressed.

[0103] In one embodiment, the positive active material layer 110 may further include a binder and a conductive material.

[0104] 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).

[0105] In one embodiment, the conductive material may include carbon-based conductive materials such as graphite, carbon nanotubes (CNTs), carbon black, and graphene; metal-based conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, and other perovskite materials.

[0106] In one embodiment, the content of the positive electrode active material particles may be 80 wt % or more, 85 wt % or more, or 90 wt % or more in the total weight of the positive electrode active material layer 110. In some embodiments, the content of the positive electrode active material particles may be 98 wt % or less or 95 wt % or less in the total weight of the positive electrode active material layer 110.

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

[0108] 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.

[0109] For example, the negative electrode active material layer 120 may include a negative electrode active material, the binder, and the conductive material.

[0110] For example, the negative electrode current collector 125 may include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof.

[0111] In one embodiment, the negative electrode active material may be a material that allows lithium ions to be inserted and extracted. For example, the negative electrode active material may include a lithium alloy, a carbon-based active material, a silicon-based active material, etc.

[0112] For example, the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0113] For example, the carbon-based active material may include crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.

[0114] For example, the amorphous carbon may include hard carbon, coke, mesocarbon microbeads, mesophase pitch-based carbon fibers, etc.

[0115] 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.

[0116] For example, the silicon-based active material may include Si, SiO x (0 < x < 2), Si / C, SiO / C, Si Metal, etc.

[0117] In some embodiments, the area of the negative electrode 130 may be larger than the area of the positive electrode 100.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] For example, the electrode assembly 150 and the electrolyte may be housed together in the pouch case 160 to form a lithium secondary battery.

[0124] In one embodiment, the electrolyte may include a lithium salt and an organic solvent.

[0125] 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 .

[0126] 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.

[0127] In an exemplary embodiment, 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. For example, the lithium secondary battery can be at 4.5V (relative to Li / Li + ) or less. 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. Therefore, the voltage decay and energy reduction of the lithium secondary battery can be suppressed.

[0128] 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.

[0129] 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 + ).

[0130] In one embodiment, the D value of the lithium secondary battery represented by the following Formula 1 may be greater than 0 and less than 0.31. Within the above range, voltage decay of the lithium secondary battery may be further suppressed.

[0131] [Formula 1]

[0132] D = I (Mn 3+ ) / [I(Mn 3+ )+I(Mn 4+ )]

[0133] In Formula 1, I(Mn 3+) is the Mn in the XPS analysis spectrum when the lithium secondary battery is charged and discharged 100 times in the voltage range of 2.0 V to 4.5 V at 45° C. and disassembled, and the positive electrode active material layer is analyzed by X-ray photoelectron spectroscopy (XPS). 3+ The area of ​​the peak. And, I(Mn 4+ ) is Mn in the XPS analysis spectrum 4+ The area of ​​the peak.

[0134] In some embodiments, the D value may be greater than 0 and less than 0.3, greater than 0 and less than 0.29, or greater than 0 and less than 0.27. Alternatively, the D value may be 0.05 to 0.3, 0.05 to 0.29, or 0.05 to 0.27. Within the above range, the voltage decay of the lithium secondary battery can be further suppressed.

[0135] Figure 3 is a schematic flowchart illustrating an operating method of a lithium secondary battery according to an exemplary embodiment.

[0136] Reference Figure 3 A lithium secondary battery including a positive electrode and a negative electrode may be prepared, wherein the positive electrode includes positive electrode active material particles, and the positive electrode active material particles include the perlithiated oxide particles and the coating material (eg, S10).

[0137] The step of preparing the lithium secondary battery may include charging and discharging the lithium secondary battery at a voltage of 4.4 V or more, greater than 4.5 V or more than 4.6 V (eg, S20). For example, the charging and discharging may be performed 1 to 10 times, 1 to 5 times, or 1 to 3 times.

[0138] The lithium secondary battery may be charged and discharged only in a voltage range of 4.5 V or less relative to the redox potential of lithium (eg, S30 ).

[0139] For example, S20 may correspond to the activation stage in the lithium secondary battery manufacturing process. In addition, S30 may correspond to the actual working stage (i.e., the actual use stage) of the lithium secondary battery. By limiting the working upper limit voltage of the actual working stage of the lithium secondary battery to below 4.5V, the voltage decay of the lithium secondary battery can be suppressed.

[0140] 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.

[0141] Production Example 1

[0142] (1) Preparation of perlithiated oxide particles

[0143] 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 40:60.

[0144] NaOH (precipitant) and NH 4 OH (chelating agent) were further added to the reactor, and a coprecipitation reaction was performed for 72 hours to prepare metal hydroxide particles.

[0145] The metal hydroxide particles were dried at 100° C. for 12 hours and then dried again at 120° C. for 12 hours.

[0146] The metal hydroxide particles and lithium hydroxide are added to a dry mixer, thereby preparing a mixture.

[0147] 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.

[0148] 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 4 hours to perform primary calcination.

[0149] After the primary calcination, the temperature of the calcination furnace was increased to 900° C. at a rate of 2° C. / min and maintained at 900° C. for 9 hours to perform secondary calcination.

[0150] During the primary calcination and the secondary calcination, oxygen was continuously introduced into the calcination furnace at a flow rate of 10 mL / min.

[0151] After the calcination, the calcined product is naturally cooled to room temperature, and then crushed and classified to prepare perlithiated oxide particles.

[0152] 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.

[0153] (2) Coating of perlithiated oxide particles

[0154] The perlithiated oxide particles and H3BO3 were added to a dry high-speed mixer and uniformly mixed for 5 minutes to prepare a mixture.

[0155] The mixture was placed in a calcining furnace, heated to 350° C. at a rate of 3° C. / min, and maintained at 350° C. for 5 hours. During the heating and temperature maintenance process, oxygen was continuously introduced at a flow rate of 10 mL / min.

[0156] After the calcination is completed, the calcined product is naturally cooled to room temperature, thereby preparing perlithiated oxide particles coated with boron.

[0157] The content of B in the boron-coated perlithiated oxide particles was measured to be 1800 ppm (ICP analysis) based on the total weight of all elements (ie, Ni, Mn and B) except lithium and oxygen.

[0158] (3) Production of initial lithium secondary battery (coin-type half-cell)

[0159] The perlithiated oxide particles as a positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder 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] (4) Initial activation of lithium secondary batteries

[0165] The initial lithium secondary battery was subjected to repeated CC / CV charging (0.1C, 4.6V cut-off) and CC discharging (0.1C, 2.0V cut-off) twice at 25°C to activate the overlithiated oxide particles.

[0166] Production Example 2

[0167] A lithium secondary battery was manufactured by the same method as in Manufacturing Example 1, except that during calcination, primary calcination was not performed, and only secondary calcination was performed for 13 hours.

[0168] Production Example 3

[0169] A lithium secondary battery was manufactured by the same method as in Manufacturing Example 1, except that B was not coated on the overlithiated oxide particles.

[0170] Examples and Comparative Examples

[0171] According to the following Table 1, the type of lithium secondary battery (Manufacturing Example 1, Manufacturing Example 2 or Manufacturing Example 3) and the cycle upper limit voltage (4.5V or 4.6V, relative to Li / Li + ) to make different settings.

[0172] Experimental Example 1: Evaluation of Voltage Attenuation

[0173] The lithium secondary batteries of the examples and comparative examples were subjected to CC / CV charging (1C, cutoff according to the upper limit voltage of Table 1) and CC discharging (1C, cutoff at 2.0V) at 45°C.

[0174] The charging and the discharging were repeated 100 times.

[0175] The average discharge voltages of the discharge curves of the 1st cycle and the 100th cycle are calculated respectively, and then the absolute value of the difference between the average discharge voltages is calculated.

[0176] Experimental Example 2: XPS Analysis

[0177] After completing the evaluation according to Experimental Example 1, the lithium secondary batteries of the examples and comparative examples were disassembled to obtain positive electrodes.

[0178] The positive electrode active material layer of the positive electrode was analyzed by XPS.

[0179] The XPS analysis apparatus and measurement conditions are as follows.

[0180] ESCALAB 250xi, Thermo Fisher Scientific

[0181] X-ray: Al Kα (Al k alpha), 1486.68 eV, beam size 500 μm,

[0182] Analyzer: CAE mode,

[0183] Number of scans: 20 Narrow Scan,

[0184] Pass energy: 20eV

[0185] Based on the XPS analysis value, the D value of the following formula 1 was calculated.

[0186] [Formula 1]

[0187] D = I (Mn 3+ ) / [I(Mn 3+ )+I(Mn 4+ )]

[0188] In Formula 1, I(Mn 3+ ) is the Mn in the XPS analysis spectrum 3+ Peak area, I(Mn 4+ ) is Mn 4+ The area of ​​the peak.

[0189] [Table 1]

[0190]

[0191] Referring to Table 1, the voltage decay of the lithium secondary battery of the embodiment is suppressed compared with the lithium secondary battery of the comparative example.

[0192] 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 lithium secondary battery, comprising: a positive electrode, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer being formed on the positive electrode current collector and containing positive electrode active material particles; and a negative electrode, the negative electrode being arranged opposite to the positive electrode, The positive electrode active material particles include perlithiated oxide particles represented by Chemical Formula 1 and a coating material, wherein the coating material is formed on at least a portion of the surface of the perlithiated oxide particles, and the coating material contains a coating element. The upper limit voltage of the lithium secondary battery is 4.5 V or less relative to the redox potential of lithium. [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.

2. The lithium secondary battery according to claim 1, wherein The D value of the lithium secondary battery represented by Formula 1 is greater than 0 and less than 0.31, [Formula 1] D=I(Mn 3+ ) / [I(Mn 3+ )+I(Mn 4+ )] In Formula 1, I(Mn 3+ ) is the Mn in the XPS analysis spectrum when the lithium secondary battery is charged and discharged 100 times in the voltage range of 2.0 V to 4.5 V at 45° C. and disassembled, and the positive electrode active material layer is analyzed by X-ray photoelectron spectroscopy (XPS). 3+ Peak area; I(Mn 4+ ) is Mn in the XPS analysis spectrum 4+ The area of ​​the peak.

3. The lithium secondary battery according to claim 1, wherein The manganese content in the perlithiated oxide particles is 50-75 mol % of all elements except lithium and oxygen.

4. The lithium secondary battery according to claim 1, wherein The content of cobalt in the perlithiated oxide particles is less than 2 mol % of all elements except lithium and oxygen.

5. The lithium secondary battery according to claim 1, wherein The overlithiated oxide particles include at least one of Li2MnO3 domains and domains derived from Li2MnO3 domains.

6. The lithium secondary battery according to claim 5, wherein: The domain derived from the Li2MnO3 domain includes at least one selected from the group consisting of MnO2, Mn2O4, LiMnO2, LiMn2O4 and Li2Mn2O4.

7. The lithium secondary battery according to claim 1, wherein: The coating element includes at least one selected from B, Al, W, Zr, Ti, Mg and Co.

8. The lithium secondary battery according to claim 1, wherein The content of the coating element in the positive electrode active material particles is 500-8000 ppm based on the total weight of all elements except lithium and oxygen.

9. The 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.

10. The lithium secondary battery according to claim 1, wherein The operating voltage range of the lithium secondary battery is 2.0V to 4.5V relative to the redox potential of lithium.

11. A method for operating a lithium secondary battery, comprising the following steps: preparing a lithium secondary battery, the lithium secondary battery comprising a positive electrode and a negative electrode, the positive electrode comprising positive electrode active material particles, the positive electrode active material particles comprising perlithiated oxide particles represented by Chemical Formula 1 and a coating material, the coating material being formed on at least a portion of a surface of the perlithiated oxide particles, and the coating material containing a coating element; as well as The lithium secondary battery is charged and discharged only in a voltage range of 4.5 V or less relative to the redox potential of lithium, [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.

12. The operating method of a lithium secondary battery according to claim 11, wherein: The step of preparing the lithium secondary battery includes charging and discharging the lithium secondary battery at a voltage greater than 4.5 V relative to the oxidation-reduction potential of lithium, once to ten times.

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