Positive electrode active material, positive electrode active material slurry, positive electrode, lithium ion secondary battery, and method for manufacturing positive electrode active material

Abstract

To provide a cathode active material for a lithium ion secondary battery having excellent cycle characteristics at high temperatures.SOLUTION: Provided according to an embodiment of the present invention is a cathode active material for a lithium ion secondary battery that comprises: a lithium transition metal oxide; and an iodine-containing material at least partially covering particles of the lithium transition metal oxide and containing iodine having an oxidation number from +3 to +7 inclusive.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a positive electrode active material, a positive electrode active material slurry, a positive electrode, a lithium ion secondary battery, and a method for producing a positive electrode active material. [Background technology]

[0002] With the advancement of technological development in mobile devices, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium-ion secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, are commercially available and widely used. Currently, vigorous research is being conducted to increase the capacity of such lithium-ion secondary batteries.

[0003] However, when increasing the capacity of such lithium ion secondary batteries, there are cases where the life characteristics (also called cycle characteristics) at high temperatures are not sufficiently obtained, and further improvement in these characteristics is desired. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-084673 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-016302 [Patent Document 3] Japanese Patent Application Publication No. 2017-183101 [Patent Document 4] Japanese Patent Application Publication No. 2018-516458 [Patent Document 5] Japanese Patent Application Laid-Open No. 2013-543219 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a positive electrode active material for a lithium ion secondary battery that has excellent cycle characteristics at high temperatures, a positive electrode active material slurry, a positive electrode, a lithium ion secondary battery, and a method for producing a positive electrode active material. [Means for solving the problem]

[0006] According to one aspect of the present invention, a positive electrode active material for a lithium-ion secondary battery is provided, comprising a lithium transition metal oxide and an iodine-containing material containing iodine having an oxidation state of +3 or more and +7 or less, at least partially coating particles of the lithium transition metal oxide. As used herein, "lithium transition metal oxide" refers to a compound containing lithium and a transition metal and having a transition metal-oxygen bond, including compounds containing typical metal elements such as aluminum and non-metal elements such as iodine. Furthermore, "iodine-containing material" refers to any material containing iodine. Furthermore, "coating" refers to at least partially covering the target surface, and includes both chemical bonding to the particle surface and physical coating of the particle surface without chemical bonding. For example, if a peak attributable to the iodine-containing material is detected in X-ray photoelectron spectroscopy (XPS) of the particle surface of the active material, it can be considered "coated."

[0007] In the positive electrode active material according to the above embodiment, the iodine-containing material may contain iodine having an oxidation number of +5 or more and +7 or less.

[0008] In the positive electrode active material according to the above embodiment, the iodine-containing material may contain iodine with an oxidation number of +7.

[0009] In the positive electrode active material according to the above aspect, the iodine-containing material may contain periodate ions or hydrogen periodate ions.

[0010] In the positive electrode active material according to the above aspect, the iodine-containing material contains periodate ions IO4 - may include:

[0011] In the positive electrode active material according to the above aspect, I3d 5 / 2 The spectrum may have a peak between 622 eV and 626 eV.

[0012] In the positive electrode active material according to the above aspect, the content of the iodine-containing material in the positive electrode active material may be 0.001% by weight or more and 10.0% by weight or less.

[0013] According to another aspect of the present invention, there is provided a positive electrode active material slurry for a lithium ion secondary battery, which includes the positive electrode active material according to the above aspect.

[0014] According to another aspect of the present invention, there is provided a positive electrode for a lithium ion secondary battery, in which a positive electrode active material layer containing the positive electrode active material according to the above aspect is formed on a current collector.

[0015] According to another aspect of the present invention, there is provided a lithium ion secondary battery comprising the positive electrode according to the above aspect.

[0016] According to another aspect of the present invention, there is provided a method for producing a positive electrode active material for a lithium-ion secondary battery, the method comprising: mixing a lithium transition metal oxide and an iodine-containing raw material in a solid state to prepare an iodine-containing mixture; and calcining the iodine-containing mixture. In this specification, the term "iodine-containing raw material" refers to a raw material that contains iodine before being calcined with the lithium transition metal oxide.

[0017] In the method for producing a positive electrode active material according to the above aspect, the iodine-containing raw material is selected from the group consisting of elemental iodine (I2), lithium iodide (LiI), sodium iodide (NaI), potassium iodide (KI), iodoform (CHI3), carbon tetraiodide (CI4), ammonium iodide (NH4I), iodic acid (HIO3), lithium iodide (LiIO3), sodium iodide (NaIO3), potassium iodate (KI The iodine-containing compound may comprise one or more selected from the group consisting of iodine(IV) oxide (IO), iodine(V) oxide (IO), iodine(IV,V) oxide (IO), iodine(IV,V) oxide (IO).

[0018] In the method for producing a positive electrode active material according to the above aspect, the iodine-containing raw material may contain elemental iodine.

[0019] In the method for producing a positive electrode active material according to the above aspect, the iodine-containing raw material may be mixed with the lithium transition metal oxide so as to be 0.01% by weight or more and 5% by weight or less relative to the lithium transition metal oxide.

[0020] In the method for producing a positive electrode active material according to the above aspect, the firing step may be performed in air.

[0021] In the method for producing a positive electrode active material according to the above aspect, the firing step may include a process of firing the iodine-containing mixture at a firing temperature of 150°C or higher and 500°C or lower.

[0022] In the method for producing a positive electrode active material according to the above aspect, in the baking step, the baking time during which the iodine-containing mixture is maintained at the baking temperature may be 1 hour or more and 12 hours or less. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a positive electrode active material for a lithium ion secondary battery, which has excellent cycle characteristics at high temperatures, a positive electrode active material slurry, a positive electrode, a lithium ion secondary battery, and a method for producing the positive electrode active material. [Brief explanation of the drawings]

[0024] [Figure 1] 1 shows a portion of the XPS spectra of the positive electrode active materials of Example 1-1 and Comparative Example 1. [Figure 2] 1 shows the transition of the change in battery capacity during the 1st to 50th charge / discharge processes in Examples 1-1 to 1-3. [Figure 3] 1 shows the transition of the change in battery capacity during the 1st to 50th charge / discharge processes in Examples 2-1 to 2-3. [Figure 4] 1 shows the transition of the change in battery capacity during the 1st to 50th charge / discharge processes in Comparative Examples 1 to 3. [Figure 5] 1 shows the XPS spectrum of I3d5 / 2 for Example 1-1 and Reference Example 1, in which coating was performed using I (iodine) or H5IO6 as the coating raw material. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited to this.

[0026] The problem of high-temperature life characteristics that can arise as the capacity of lithium-ion secondary batteries increases will be explained using as an example a lithium-ion secondary battery that uses a lithium transition metal oxide with a high nickel content as the positive electrode material.

[0027] As a positive electrode material for lithium-ion secondary batteries, Li a Ni x Co y Mn zIt is known that increasing the amount of nickel in lithium-nickel-cobalt-manganese ternary cathode active materials, such as LiCoO2, can increase their capacity. In fact, the market is constantly demanding ever-higher capacity lithium-ion secondary batteries, and the development of Ni-rich cathode active materials with high capacity per unit weight in the operating voltage range of 3.0 V to 4.2 V is actively being pursued to replace the conventionally used LiCoO2. However, as the amount of Ni increases in lithium-nickel-cobalt-manganese ternary cathode active materials, problems such as gas generation at high temperatures and decreased stability in the charged state arise, posing major challenges to their application in actual batteries.

[0028] To address these issues, methods have been proposed for forming a protective coating of insulating metal oxides such as alumina or titania on the particle surface of positive electrode active material to suppress gas generation and achieve stable cycling behavior, as described in Patent Documents 1 and 2. However, Ni-rich positive electrodes, which contain a large amount of Ni, are significantly affected by the increased resistance caused by such coating treatments. Depending on the treatment, this can lead to not only reduced discharge capacity and rate characteristics but also deterioration of cycling characteristics. On the other hand, as described in Patent Documents 3 and 4, methods such as the sol-gel method, pulsed laser deposition (PLD), chemical vapor deposition (CVD), and atomic layer deposition (ALD) have been used to minimize the resistance caused by the coating, but their application to actual batteries is currently difficult due to cost and mass production considerations. Furthermore, as described in Patent Document 5, attempts have been made to coat LiMnO2 with metal halides such as AlF3, AlBr3, and AlI3 by reacting an ammonium halide with an Al source in an aqueous solution. However, the higher the Ni content of ternary positive electrode active materials, the lower their water stability becomes. Exposure to water leads to the dissolution of Li, resulting in significant degradation of performance. Furthermore, there are concerns about the dissolution of the active material when using aqueous solutions of highly oxidizing ammonium halides. Thus, there are currently very few coating technologies available that meet both cost and performance requirements for active materials currently in use or under development.

[0029] The present inventors have found that when a positive electrode active material containing a lithium transition metal oxide is used in a lithium ion secondary battery, the addition of an iodine-containing material containing iodine having an oxidation number of +3 or more and +7 or less can suppress deterioration of the cycle characteristics of the lithium ion secondary battery at high temperatures, and have completed the present invention.

[0030] [Lithium-ion secondary battery] A lithium ion secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The lithium ion secondary battery may also optionally include a battery case that houses the electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery case.

[0031] [Positive electrode] In the lithium-ion secondary battery according to the embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on one or both surfaces of the positive electrode current collector. The positive electrode active material layer may be formed on the entire surface of the positive electrode current collector, or may be formed on only a portion of the surface. For example, the positive electrode according to the embodiment is a positive electrode for a lithium-ion secondary battery containing an electrolyte solution.

[0032] (Positive electrode current collector) The positive electrode current collector used in the positive electrode is not particularly limited as long as it is electrochemically stable and conductive. For example, the positive electrode current collector may be stainless steel, aluminum, nickel, titanium, or an alloy thereof, or a mixture of one or more of these. Furthermore, baked carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, or the like may also be used.

[0033] The positive electrode current collector may have a thickness of 3 μm to 500 μm. Microscopic irregularities may be formed on the surface of the positive electrode current collector to enhance adhesion to the positive electrode active material. The positive electrode current collector may have various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0034] (Cathode active material layer) The positive electrode active material layer can be formed by applying a positive electrode active material slurry, in which a mixture of a positive electrode active material, a conductive agent, and a binder is dissolved and dispersed in a solvent, to a positive electrode current collector, followed by drying and rolling.

[0035] (Cathode active material) The positive electrode active material may include a lithium transition metal oxide capable of absorbing and releasing lithium and an iodine-containing material, as described below. The positive electrode active material may include, for example, a lithium transition metal oxide containing nickel, preferably a lithium transition metal oxide with a high nickel content. Here, "high nickel content" refers to the inclusion of 50 mol% or more of nickel based on the total amount of transition metals. As described above, high-nickel lithium transition metal oxides, such as those containing 50 mol% or more of nickel, are known to have issues with high-temperature cycle performance. Therefore, by using the positive electrode active material according to this embodiment to improve high-temperature cycle performance, it is possible to achieve both high capacity and high-temperature cycle performance in a lithium-ion secondary battery. For example, the positive electrode active material may include a lithium transition metal oxide containing 60 mol% or more, 70 mol% or more, 80 mol% or more, or 90 mol% or more of nickel based on the total amount of transition metals.

[0036] The content of the positive electrode active material may be 80 wt % or more and 99.5 wt % or less based on the total weight of the positive electrode active material layer. The content of the positive electrode active material may preferably be 85 wt % or more and 98.5 wt % or less. When the content of the positive electrode active material is within the above range, excellent capacity characteristics can be realized. On the other hand, when the content of the positive electrode active material is less than the above range, the coating amount of the positive electrode increases, the thickness increases, and a sufficient volumetric energy density may not be achieved. When the content of the positive electrode active material is greater than the above range, the binder and conductive material may be insufficient, resulting in insufficient electrode conductivity and adhesive strength, which may result in reduced battery performance.

[0037] (Lithium transition metal oxides) Examples of lithium transition metal oxides include lithium-manganese-based oxides (e.g., LiMnO2, LiMnO3, LiMn2O3, LiMn2O4, etc.); lithium-cobalt-based oxides (e.g., LiCoO2, etc.); lithium-nickel-based oxides (e.g., LiNiO2, etc.); lithium-copper-based oxides (e.g., Li2CuO2, etc.); lithium-vanadium-based oxides (e.g., LiV3O8, etc.); lithium-nickel-manganese-based oxides (e.g., LiNi 1-z Mn z O2(0 < z < 1), LiMn 2-z Ni z O4(0 < z < 2), etc.); lithium-nickel-cobalt-based oxides (e.g., LiNi 1-y Co y O2(0 < y < 1), etc.); lithium-manganese-cobalt-based oxides (e.g., LiCo 1-z Mn z O2(0 < z < 1), LiMn 2-y Co y O4(0 < y < 2), etc.); lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni x Co y Mn​​​​​​​​​​​​​​​​​​​​​)O2(0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1, 0 < p < 1); Examples include compounds in which the transition metal element in these compounds is partially substituted with one or more other metal elements. The positive electrode active material layer can contain any one or two or more of these compounds, but is not limited thereto.

[0038] In particular, as an example of a lithium transition metal oxide having a high nickel content effective for increasing the capacity of the battery, Li a NiO2(0.5 ≦ a ≦ 1.5); Li a (Ni x Co y Mn z )O2(0.5 ≦ a ≦ 1.5, 0.5 ≦ x < 1, 0 < y < 0.5, 0 < z < 0.5, x + y + z = 1); Li a (Ni x Co y Mn z )O2(0.7 ≦ x < 1, 0 < y < 0.3, 0 < z < 0.3, x + y + z = 1); Li a (Ni x Co y Mn z )O2(0.8 ≦ x < 1, 0 < y < 0.2, 0 < z < 0.2, x + y + z = 1); Li a [[ID=CAUTION]] (Ni x Co y Mn z )O2(0.9 ≦ x < 1, 0 < y < 0.1, 0 < z < 0.1, x + y + z = 1); Li a Ni 1-y Co y O2(0.5 ≦ a ≦ 1.5, 0 < y ≦ 0.5); Li a Ni 1-z Mn z O2(0.5 ≦ a ≦ 1.5, 0 < z ≦ 0.5); Li a (Ni x Co y Mn z )O4(0.5 ≦ a ≦ 1.5, 1 ≦ x < 2, 0 < y < 1, 0 < z < 1, x + y + z = 2); Li a (Ni x Co y M w 请注意,原文中可能存在一些格式或内容上的不规范之处,比如突然出现的“[[ID=CAUTION]] ”,我按照要求完整保留了所有内容进行翻译。如果这是一个错误标记,你可以根据实际情况进行调整。)O2(M is one or more elements selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, Mo, Zr, Zn, Ga, and In, 0.5 ≦ a ≦ 1.5, 0.5 ≦ x < 1, 0 < y < 0.5, 0 < w < 0.5, x + y + w = 1); Li a (Ni x Co y Mn z M w )O2(M is one or more elements selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, Mo, Zr, Zn, Ga, and In, 0.5 ≦ a ≦ 1.5, 0.5 ≦ x < 1, 0 < y < 0.5, 0 < z < 0.5, 0 < w < 0.5, x + y + z + w = 1); compounds in which at least part of the transition metal atoms are substituted with one or more other metal elements (for example, one or more of Al, Fe, V, Cr, Ti, Ta, Mg, Mo, Zr, Zn, Ga, and In); compounds in which oxygen atoms in these compounds are partially substituted with one or more other non-metal elements (for example, one or more of P, F, S, and N), etc. The positive electrode active material can include one or more of these, but is not limited thereto. Also, even within the same particle, there may be a concentration distribution of substitution between the inside and the surface layer. Also, it may be coated on the surface of the particle. For example, surfaces coated with metal oxides, lithium transition metal oxides, polymers, etc. can be mentioned, but it is not limited thereto.

[0039] In particular, in terms of improving the capacity characteristics and stability of the battery, Li a NiO2, Li a (Ni 0.5 Mn y Co z )O2(y + z = 0.5), Li a (Ni 0.6 Mn y Co z )O2(y + z = 0.4), Li a (Ni 0.7 Mn y Co z )O2(y + z = 0.3), Li a (Ni 0.8 Mny Co z )O2(y+z=0.2), Li a (Ni 0.8 Co y Mn z Al w )O2(y+z+w=0.2), Li a (Ni 0.85 Co y Mn z )O2(y+z=0.15), Li a (Ni 0.85 Co y Mn z Al w )O2(y+z+w=0.15), Li a (Ni 0.9 Co y Mn z )O2(y+z=0.1), Li a (Ni 0.9 Co y Mn z Al w )O2(y+z+w=0.1), Li a (Ni 0.9 Co y Mn z )O2(y+z=0.1), Li a (Ni 0.95 Co y Mn z Al w )O2(y+z+w=0.05), etc. are preferred, where the value of a can be, for example, 0.5≦a≦1.5, and preferably 1.0≦a≦1.5.

[0040] More specifically, LiNiO2, Li(Ni 0.5 Mn 0.3 Co 0。2 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.8 Co 0.15 Al 0.05)O2, Li(Ni 0.8 Co 0.1 Mn 0.05 Al 0.05 )O2, Li(Ni 0.85 Co 0.10 Mn 0.05 )O2, Li(Ni 0.85 Co 0.10 Mn 0.03 Al 0.02 )O2, Li(Ni 0.9 Co 0.05 Mn 0.05 )O 2、 Li(Ni) 0.9 Co 0.05 Al 0.05 )O2, Li(Ni 0.95 Co 0.03 Mn 0.02 )O2, Li(Ni 0.95 Co 0.03 Al 0.02 )O2 etc. are preferred.

[0041] (Iodine-containing materials) The positive electrode active material according to this embodiment includes an iodine-containing material in addition to a lithium transition metal oxide. In this embodiment, the iodine-containing material is obtained by mixing a lithium transition metal oxide with an iodine-containing raw material and calcining the mixture. That is, the positive electrode active material obtained by calcination includes a lithium transition metal oxide (which does not necessarily have to be the same as the lithium transition metal oxide used as the raw material before calcination) and an iodine-containing material on the lithium transition metal oxide. The iodine-containing material in the positive electrode active material may exist independently of the lithium transition metal oxide particles, or may be at least partially chemically or physically bonded to the surface of the lithium transition metal oxide particles. It is preferable that the iodine-containing material is at least partially in contact with the lithium transition metal oxide particles. Alternatively, the iodine-containing material may be at least partially incorporated into the structure of the lithium transition metal oxide. The iodine-containing material is not limited to an independent compound, but may be any chemical species, such as an ion, an atom, or an atomic group.

[0042] The content of the iodine-containing material in the positive electrode active material is, for example, 0.001% by weight to 10.0% by weight, preferably 0.01% by weight to 1.0% by weight, more preferably 0.02% by weight to 0.5% by weight, and even more preferably 0.05% by weight to 0.2% by weight. If the content of the iodine-containing material is 0.001% by weight or more, improvements in the cycle characteristics and electrical characteristics of the battery are expected.

[0043] The iodine-containing raw material is a raw material for introducing iodine into the positive electrode active material. The iodine-containing raw material is preferably a solid at room temperature, since it can be easily mixed with the lithium transition metal oxide. For example, iodine-containing raw materials include elemental iodine (I2), lithium iodide (LiI), sodium iodide (NaI), potassium iodide (KI), iodoform (CHI3), carbon tetraiodide (CI4), ammonium iodide (NH4I), iodic acid (HIO3), lithium iodide (LiIO3), sodium iodide (NaIO3), potassium iodate (KIO3), ammonium iodate (NH4IO3), metaperiodic acid (HIO4), orthoperiodic acid (H5IO6), lithium periodate (LiIO4), sodium periodate (NaIO4), potassium periodate (KIO4), iodine(IV) oxide (IO2), iodine(V) oxide (IO2), and iodine(IV,V) oxide (IO4O9). In addition, any iodine-containing material can be used, such as metal iodide or an iodine-containing organic compound, as long as it does not significantly adversely affect the battery characteristics. The valence of iodine in the iodine-containing raw material is not particularly limited.

[0044] The iodine-containing material in the positive electrode active material after firing contains iodine having an oxidation number of +3 or more and +7 or less. The iodine-containing material contains, for example, iodine having an oxidation number of +5 or more and +7 or less, and more preferably iodine having an oxidation number of +7. Iodine having an oxidation number of +3 or more and +7 or less often has strong oxidizing power. For example, examples of iodine compounds having an oxidation state of +3 or greater and +7 or less include iodic acid (HIO), lithium iodine (LiIO), sodium iodine (NaIO), potassium iodate (KIO), ammonium iodate (NHIO), metaperiodic acid (HIO), orthoperiodic acid (HIO), lithium periodate (LiIO), sodium periodate (NaIO), potassium periodate (KIO), iodine(IV) oxide (IO), iodine(V) oxide (IO), and iodine(IV,V) oxide (IO). The iodine-containing material may contain periodate ions or hydrogen periodate ions. Examples of periodate ions include metaperiodate ions, such as IO. - , orthoperiodate ion IO6 5- The hydrogen periodate ion is HIO6 4- , H2IO6 3- , H3IO6 2- , H4IO6 - Examples include:

[0045] The spectrum observed by X-ray photoelectron spectroscopy (XPS) of the positive electrode active material shows the I3d 5 / 2 It has a peak due to electrons. -(CH2) n When charge correction is performed with the energy of the C1s peak top derived from iodine set to 284.6 eV, the position of this peak is preferably 622 eV to 626 eV, more preferably 623 eV to 625 eV, and even more preferably 623.5 eV to 624.5 eV. Here, "peak position" refers to the position (energy) of the maximum value of the peak. This peak is derived from iodine having an oxidation number of +3 to +7, more preferably from iodine having an oxidation number of +5 to +7, and even more preferably from iodine having an oxidation number of +7.

[0046] The iodine-containing material preferably at least partially coats the lithium transition metal oxide particles. Preferably, at least a portion of the iodine-containing material at least partially coats the surface of the lithium transition metal oxide particles, and more preferably is chemically or physically bonded to the surface of the lithium transition metal oxide particles. The thickness of the coating is not particularly limited.

[0047] It is speculated that the iodine-containing material can suppress the cycle deterioration of the battery through the following mechanism, however, the following is merely an exemplary speculation to aid in understanding the invention and is not intended to limit the present invention in any way.

[0048] When lithium transition metal oxides and iodine-containing raw materials are mixed and sintered, the iodine-containing raw materials undergo a chemical reaction to form an iodine-containing material, although the details are unclear. The function of the iodine-containing material in the positive electrode active material is also unclear, but as mentioned above, the resulting iodine-containing material may contain iodine, which has an oxidation state of +3 or greater and +7 or less, and has strong electron-withdrawing properties. Previous findings have shown that mixing LiI into a solid electrolyte improves Li-ion conductivity by attracting electrons to the highly electronegative I. Based on these findings, it is speculated that the iodine-containing material improves Li conductivity and promotes the redox reaction of the positive electrode active material during the charging process. As a result, side reactions such as electrolyte decomposition that occur during the charging process are suppressed, suppressing an increase in the positive electrode resistance and resulting in a stable, long-term battery cycle.

[0049] The resulting iodine-containing material is believed to form at least a partial coating on the surface of the lithium transition metal oxide particles. This coating suppresses the chemical reaction between the positive electrode material and the electrolyte, thereby suppressing the formation of side reaction products. This is thought to suppress adverse effects such as inhibition of the battery reaction due to the formation of side reaction products on the positive electrode active material with repeated charge / discharge, an increase in the battery's electrical resistance, and gas generation that causes battery expansion.

[0050] As will be shown in the examples below, the effect of suppressing the deterioration of the battery characteristics as described above was confirmed at high temperatures of 45° C. to 60° C. That is, in this embodiment, by using a positive electrode active material containing an iodine-containing material, it is possible to suppress the deterioration of cycle characteristics at high temperatures.

[0051] (binder) The binder is added as a component that promotes bonding between the active material and the conductive agent, bonding with the current collector, etc. Examples of binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and one or a mixture of two or more of these may be used, but the binder is not limited to these.

[0052] The binder content may be 0.1 wt % to 30 wt % based on the total weight of the positive electrode active material layer. The binder content may be preferably 0.5 wt % to 15 wt %, more preferably 0.5 wt % to 5 wt %. When the binder polymer content satisfies the above range, sufficient adhesive strength within the electrode can be imparted while preventing a decrease in the capacity characteristics of the battery.

[0053] (Conductive agent) The conductive agent is not particularly limited as long as it is an electrically conductive material that does not induce chemical changes. Examples of conductive agents include carbon-based materials such as artificial graphite, natural graphite, carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, furnace black, lamp black, carbon nanotubes, and carbon fibers; metal powders and metal fibers such as aluminum, tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lanthanum, ruthenium, platinum, and iridium; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyaniline, polythiophene, polyacetylene, polypyrrole, and polyphenylene derivatives. These may be used alone or in combination, but the conductive agent is not limited thereto.

[0054] The content of the conductive agent may be 0.1 wt % or more and 30 wt % or less based on the total weight of the positive electrode active material layer. The content of the conductive agent may be preferably 0.5 wt % or more and 15 wt % or less, and more preferably 0.5 wt % or more and 5 wt % or less. When the content of the conductive agent satisfies the above range, sufficient conductivity can be imparted and the amount of positive electrode active material is not reduced, which is advantageous in that battery capacity can be secured.

[0055] (solvent) The solvent used in the positive electrode active material slurry is not particularly limited as long as it is one generally used in the production of a positive electrode. Examples of the solvent include amine solvents such as N,N-dimethylaminopropylamine, diethylenetriamine, and N,N-dimethylformamide (DMF), ether solvents such as tetrahydrofuran, ketone solvents such as methyl ethyl ketone, ester solvents such as methyl acetate, amide solvents such as dimethylacetamide and 1-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), water, etc., and one or a mixture of two or more of these may be used, but the solvent is not limited thereto.

[0056] The amount of solvent used is sufficient as long as it has a viscosity that allows the positive electrode active material, conductive material, and binder to be dissolved or dispersed while exhibiting excellent thickness uniformity when applied to the positive electrode current collector, taking into consideration the coating thickness of the slurry and the production yield.

[0057] [Method of manufacturing positive electrode active material] A method for producing a positive electrode active material for a lithium-ion secondary battery according to the embodiment may include: (1) a mixing step of mixing a lithium transition metal oxide and an iodine-containing raw material in a solid state to prepare an iodine-containing mixture; and (2) a calcination step of calcining the iodine-containing mixture.

[0058] (1) Mixing step In the mixing step, at least one lithium transition metal oxide and the iodine-containing raw material are mixed in a solid state. The resulting mixture is referred to as an "iodine-containing mixture." For example, a powdered iodine-containing mixture can be obtained by mixing a powdered lithium transition metal oxide with a powdered iodine-containing raw material. The specific mixing method is not particularly limited, and any known method can be used. The mixing step is preferably performed in the air, but may also be performed in other atmospheres. In addition, any material may be added in addition to the lithium transition metal oxide and the iodine-containing raw material. Mixing the raw materials in a solid state simplifies the mixing step, reduces costs, and is suitable for mass production.

[0059] The amount of lithium transition metal oxide added in the mixing step is, for example, 85 parts by weight to 99.99 parts by weight, preferably 90 parts by weight to 99.9 parts by weight, and more preferably 95 parts by weight to 99.5 parts by weight, assuming the total weight of the iodine-containing mixture is 100 parts by weight. The amount of iodine-containing raw material added is, for example, 0.01 parts by weight to 5 parts by weight, preferably 0.1 parts by weight to 4 parts by weight, more preferably 0.5 parts by weight to 3 parts by weight, and even more preferably 1 part by weight to 3 parts by weight. When the amount of iodine-containing raw material added is 0.01 parts by weight or more, improvements in the cycle characteristics and electrical characteristics of the battery are expected. When the amount of iodine-containing raw material added is 5 parts by weight or less, excessive side reactions are thought to be suppressed.

[0060] (2) Firing step In the calcination step, the iodine-containing mixture obtained in the mixing step is calcined to obtain a positive electrode active material. The calcination is preferably performed in the presence of oxygen, more preferably in the atmosphere, but may be performed in other atmospheres. For example, the calcination may be performed in an inert atmosphere such as a nitrogen atmosphere or a rare gas atmosphere such as argon. Calcination in the atmosphere simplifies the calcination step, reduces costs, and is suitable for mass production.

[0061] The firing temperature for firing the iodine-containing mixture is, for example, 150°C or higher and 500°C or lower, preferably 200°C or higher and 450°C or lower, more preferably 250°C or higher and 400°C or lower, and even more preferably 300°C or higher and 350°C or lower. A firing temperature of 150°C or higher is thought to promote the reaction of the iodine-containing raw material. Furthermore, a firing temperature of 500°C or lower is thought to suppress the formation of excessive side reaction products. Furthermore, the firing temperature for firing the iodine-containing mixture is preferably higher than the melting point of the iodine-containing raw material, more preferably higher than the boiling point of the iodine-containing raw material.

[0062] The calcination time during which the iodine-containing mixture is maintained at the calcination temperature is, for example, 1 hour to 12 hours, preferably 1 hour to 9 hours, more preferably 1.5 hours to 6 hours, and even more preferably 2 hours to 5 hours. A calcination time of 1 hour or more is considered to allow the iodine-containing raw material to react within the required range. Furthermore, a calcination time of 12 hours or less can reduce costs by avoiding excessively long calcination times.

[0063] [Method for producing positive electrode active material slurry and positive electrode] A conductive agent, a binder, and the like are added to the positive electrode active material obtained above. At this time, other additives such as a dispersant and a thickener may be added as necessary. By dispersing these in a solvent, a positive electrode active material slurry is obtained. That is, the positive electrode active material slurry contains the positive electrode active material obtained above, a conductive agent, a binder, and a solvent.

[0064] The positive electrode active material slurry is applied to a positive electrode current collector, followed by drying and rolling, to produce a positive electrode in which a positive electrode active material layer is formed on the positive electrode current collector.

[0065] Alternatively, the positive electrode may be produced by, for example, casting the positive electrode active material slurry onto a separate support, peeling the film from the support, and laminating the resulting film onto a positive electrode current collector. Alternatively, the positive electrode active material layer may be formed on the positive electrode current collector by any other method.

[0066] [Negative electrode] In the lithium-ion secondary battery according to the embodiment, the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector. The negative electrode active material layer may be formed on the entire surface of the negative electrode current collector, or may be formed on only a portion of the surface.

[0067] (Negative electrode current collector) The negative electrode current collector used in the negative electrode is not particularly limited as long as it is electrochemically stable and conductive. For example, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy.

[0068] The negative electrode current collector may have a thickness of 3 μm to 500 μm. Microscopic irregularities may be formed on the surface of the negative electrode current collector to enhance adhesion to the negative electrode active material. The negative electrode current collector may have various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0069] (Negative electrode active material layer) The negative electrode active material layer can be formed, for example, by applying a negative electrode active material slurry, in which a mixture of a negative electrode active material, a binder, and a conductive agent is dissolved or dispersed in a solvent, to a negative electrode current collector, followed by drying and rolling. The mixture can further contain a dispersant, a filler, and other optional additives, as necessary.

[0070] (Negative electrode active material) The negative electrode active material may be a compound capable of reversible lithium intercalation and deintercalation. Examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; silicon materials such as silicon powder, amorphous silicon, silicon nanofibers, and silicon nanowires; silicon compounds such as silicon alloys, silicon oxides, and silicon oxides doped with alkali metals or alkaline earth metals (such as lithium and magnesium); metallic materials capable of alloying with lithium, such as Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Sn alloys, and Al alloys; metal oxides capable of lithium doping and dedoping, such as SnO, vanadium oxide, and lithium vanadium oxide; and composites such as composites of silicon and carbonaceous materials and Sn-C composites. These may be used singly or in combination, but are not limited thereto. The carbonaceous material may be either low-crystalline carbon or high-crystalline carbon, etc. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, scaly, spherical, or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitch, and high-temperature-burned carbon such as petroleum- or coal-based coke.

[0071] The negative electrode active material may be contained in an amount of 80% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

[0072] (binder and conductive agent) The types and contents of the binder and conductive agent used in the negative electrode active material slurry may be the same as those described for the positive electrode.

[0073] (solvent) The solvent used in the negative electrode active material slurry is not particularly limited as long as it is one generally used in the production of negative electrodes. Examples of the solvent include, but are not limited to, N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, acetone, water, etc., and one or a mixture of two or more of these may be used.

[0074] [Method of manufacturing negative electrode] A method for manufacturing a negative electrode for a lithium ion secondary battery according to the embodiment may include the steps of: obtaining a negative electrode active material slurry by dissolving or dispersing a negative electrode active material, together with a binder, a conductive agent, and the like, as necessary, in a solvent; and obtaining a negative electrode by forming a negative electrode active material layer on a negative electrode current collector by, for example, applying the negative electrode active material slurry onto the negative electrode current collector, in the same manner as in the method for manufacturing a positive electrode.

[0075] [Separator] In the lithium ion secondary battery according to the present embodiment, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in lithium ion secondary batteries can be used without any particular limitations. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte moisture absorption are preferred. For example, porous polymer films made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, can be used as the separator. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Separators coated with ceramic components or polymeric materials to ensure heat resistance or mechanical strength may also be used.

[0076] [Non-aqueous electrolyte] In the lithium ion secondary battery according to the embodiment, examples of the non-aqueous electrolyte include organic liquid electrolytes and inorganic liquid electrolytes that can be used in the manufacture of lithium ion secondary batteries, but are not limited to these.

[0077] The non-aqueous electrolyte may contain an organic solvent and a lithium salt, and may further contain an electrolyte additive as needed. Hereinafter, the liquid electrolyte may also be referred to as an "electrolytic solution."

[0078] The organic solvent can be used without any particular limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Examples of organic solvents include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether and tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitrile-based solvents such as R-CN (R is a C2 to C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bond aromatic ring or an ether bond); amide-based solvents such as dimethylformamide; dioxolane-based solvents such as 1,3-dioxolane; and sulfolane-based solvents. These solvents may be used alone or in combination. However, the solvent is not limited to these. In particular, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate, propylene carbonate, etc.) with high ionic conductivity and high dielectric constants, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are more preferred. In this case, when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of 1:1 to 1:9, excellent electrolyte performance can be achieved.

[0079] Lithium salts can be used without particular limitations as long as they are compounds capable of providing lithium ions used in lithium-ion secondary batteries. Examples of lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, and LiB(C2O4)2, and mixtures of one or more of these can be used, but are not limited to these. The lithium salt can be contained in the electrolyte at a concentration of 0.1 mol / L to 2 mol / L, for example. When the lithium salt concentration falls within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and enabling efficient lithium ion migration.

[0080] Electrolyte additives can be used as needed to improve battery life, suppress battery capacity loss, and improve battery discharge capacity. Examples of electrolyte additives include haloalkylene carbonate compounds such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), and difluoroethylene carbonate (DFEC), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride. One or a mixture of two or more of these additives can be used, but the electrolyte additives can be present in an amount of, for example, 0.1 wt % to 15 wt % of the total weight of the electrolyte.

[0081] [Method of manufacturing lithium-ion secondary batteries] The lithium ion secondary battery according to the embodiment can be fabricated by interposing a separator (e.g., a separator membrane) and an electrolyte between the cathode and anode fabricated as described above. More specifically, the electrode assembly can be formed by disposing a separator between the cathode and anode, and then inserting the electrode assembly into a battery case such as a cylindrical battery case or a prismatic battery case, followed by injecting an electrolyte. Alternatively, the electrode assemblies can be stacked, impregnated with an electrolyte, and then inserted into a battery case and sealed.

[0082] The battery case may be any battery case commonly used in the art, and may have, for example, a cylindrical shape using a can, a rectangular shape, a pouch shape, or a coin shape.

[0083] The lithium ion secondary battery according to the embodiment can be used not only as a power source for small devices but also as a unit battery for medium- to large-sized battery modules including a large number of battery cells, etc. Preferred examples of such medium- to large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Example]

[0084] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to these examples. Furthermore, the mechanisms described below are merely exemplary speculations to aid in understanding the invention and do not limit the present invention in any way.

[0085] [Example 1-1] (Cathode manufacturing) LiNi 0.90 Co 0.07 Mn 0.03100 parts by weight of O2 (hereinafter also referred to as "lithium transition metal oxide") powder was mixed with 1.0 parts by weight of elemental iodine (I2; manufactured by Wako Pharmaceuticals) powder and sealed in a 100 mL plastic bottle. The plastic bottle was shaken up and down by hand for approximately 1 minute to mix the contents, obtaining an iodine-containing mixture. This iodine-containing mixture was heated to 300°C in air, held at 300°C for 2 hours to be calcined, and then cooled to room temperature to obtain a cathode active material. Next, 96.5 parts by weight of the above cathode active material were added with 1.5 parts by weight of carbon black as a conductive material, 2.0 parts by weight of polyvinylidene fluoride (PVDF) as a binder, and N-methyl-2-pyrrolidone (NMP) as a solvent, and mixed to obtain a cathode active material slurry.

[0086] Next, the obtained positive electrode active material slurry was applied to a 20 μm thick aluminum foil to a thickness of about 70 μm, and dried at 130° C. to obtain a positive electrode sheet.

[0087] (Electrolyte production) Ethylene carbonate, dimethyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:2:1, and LiPF6 was dissolved therein at a concentration of 1 mol / L, and 2.0 wt % vinylene carbonate (VC) was added to obtain an electrolyte solution.

[0088] (Coin cell battery manufacturing) The obtained positive electrode sheet was punched into a circle with a diameter of 13 mm to form a positive electrode for a coin cell, and a CR2016 coin cell battery was fabricated using metallic lithium with a thickness of 0.3 mm as the negative electrode and the above electrolyte.

[0089] (Manufacturing mono-cell batteries) Separately from the coin cells, the positive electrode sheet obtained as described above was punched into a square to form a positive electrode for a mono-cell, graphite of a corresponding size was used as the negative electrode, and the above-mentioned electrolyte was used to fabricate a mono-cell battery.

[0090] [Example 1-2] A positive electrode, a coin cell battery, and a mono-cell battery were produced in the same manner as in Example 1-1, except that 2.0 parts by weight of iodine was added.

[0091] [Examples 1-3] A positive electrode, a coin cell battery, and a mono-cell battery were produced in the same manner as in Example 1-1, except that 3.0 parts by weight of iodine was added.

[0092] [Example 2-1] A positive electrode, a coin cell battery, and a mono-cell battery were produced in the same manner as in Example 1-1, except that the iodine-containing mixture was baked at 350° C. for 5 hours.

[0093] [Example 2-2] A positive electrode, a coin cell battery, and a mono-cell battery were manufactured in the same manner as in Example 2-1, except that 2.0 parts by weight of iodine was added.

[0094] [Example 2-3] A positive electrode, a coin cell battery, and a mono-cell battery were manufactured in the same manner as in Example 3-1, except that 3.0 parts by weight of iodine was added.

[0095] [Example 3-1] A positive electrode, a coin cell battery, and a mono-cell battery were produced in the same manner as in Example 1-1, except that the iodine-containing mixture was baked at 400° C. for 2 hours.

[0096] [Example 3-2] A positive electrode, a coin cell battery, and a mono-cell battery were produced in the same manner as in Example 1-1, except that the iodine-containing mixture was baked at 400° C. for 5 hours.

[0097] [Example 4-1] A positive electrode, a coin cell battery, and a mono-cell battery were produced in the same manner as in Example 1-1, except that the iodine-containing mixture was baked at 450° C. for 2 hours.

[0098] [Example 4-2] A positive electrode, a coin cell battery, and a mono-cell battery were produced in the same manner as in Example 1-1, except that the iodine-containing mixture was baked at 450° C. for 5 hours.

[0099] [Comparative Example 1] A positive electrode, a coin cell battery, and a monocell battery were manufactured in the same manner as in Example 1-1, except that iodine was not added, no calcination was performed, and the raw material lithium transition metal oxide powder was used as it was as the positive electrode active material.

[0100] Comparative Example 2 A positive electrode, a coin cell battery, and a mono-cell battery were manufactured in the same manner as in Example 1-1, except that iodine was not added and a raw material lithium transition metal oxide powder was used as the positive electrode active material by calcining it at 300°C for 2 hours instead of the iodine-containing mixture.

[0101] Comparative Example 3 A positive electrode, a coin cell battery, and a mono-cell battery were produced in the same manner as in Comparative Example 2, except that the firing temperature was 350° C. and the firing time was 5 hours.

[0102] The manufacturing conditions for each of the above examples and comparative examples are summarized in Table 1 below. [Table 1]

[0103] [Evaluation Example 1: X-ray photoelectron spectroscopy (XPS) measurement of positive electrode active material] The positive electrode active materials obtained in Example 1-1 and Comparative Example 1 were measured using X-ray photoelectron spectroscopy (XPS). The samples analyzed were solid-state positive electrode active materials after calcination and before the preparation of positive electrode active material slurry. -(CH2) n The charge correction was performed with the energy of the C1s peak top derived from iodine set to 284.6 eV. FIG. 1 shows a part of the XPS spectrum of the positive electrode active material of Example 1-1 (solid line) and Comparative Example 1 (dotted line). In the positive electrode active material of Example 1-1, the 3d peak of iodine with a peak top near 624 eV was observed in the range of 622 eV to 626 eV. 5 / 2A peak derived from electrons was observed, whereas no peak was observed in the positive electrode active material of Comparative Example 1. This peak position substantially coincides with that of sodium periodate (NaIO4) containing iodine with an oxidation number of +7, so it is presumed that at least part of the iodine in the positive electrode active material is in the form of periodate ions. Note that in Example 1-1, no peak near 618 eV to 620 eV derived from iodine with an oxidation number of 0 or -1 was observed.

[0104] [Evaluation Example 2: Elemental analysis of positive electrode active material by X-ray fluorescence analysis] The positive electrode active materials obtained in each example and comparative example were subjected to elemental analysis by X-ray fluorescence analysis (XRF). A scanning X-ray fluorescence analyzer ZSX Primus II (manufactured by Rigaku) ​​was used as the X-ray fluorescence analyzer. The sample subjected to X-ray fluorescence analysis was a solid-state positive electrode active material prior to preparation of the positive electrode active material slurry. The value of Comparative Example 1-1, which was not subjected to a coating treatment, was used as a baseline. The values ​​obtained by subtracting this value from the values ​​of Examples 1-1, 2-1, 3-1, and 4-1 are shown in Table 2 below as the iodine content of each sample. [Table 2]

[0105] [Evaluation example 3: Capacity retention rate at high temperature (30 cycles)] The coin cell batteries manufactured in each Example and Comparative Example 1 were subjected to 30 charge / discharge cycles in a thermostatic chamber maintained at 45° C., with a charge upper limit voltage of 4.25 V and a discharge lower limit voltage of 2.50 V, at a charge current rate of 0.3 C and a discharge current rate of 0.3 C. Generally, the capacity retention rate after the nth charge / discharge cycle is defined by the following formula:

number

[0106] The capacity retention rate (45°C) after the 30th cycle is shown in Table 3. The deterioration of the battery capacity was greatest in Comparative Example 1 and least in Examples 1-3. [Table 3]

[0107] [Evaluation example 4: Capacity retention rate at high temperature (300 cycles)] The mono-cell batteries manufactured in Examples 1-1 to 1-3, Examples 2-1 to 2-3, and Comparative Examples 1 to 3 were subjected to a charge / discharge process 300 times in a thermostatic chamber maintained at 45°C, with a charge upper limit voltage of 4.25V and a discharge lower limit voltage of 2.50V, at a charge current rate of 0.3C and a discharge current rate of 0.3C.

[0108] The values ​​of the capacity retention rate defined above were plotted against the number of charge-discharge cycles. The graphs showing the change in battery capacity over time from the first to the 50th charge-discharge cycle are shown in Figures 2 to 4. Figure 2 shows the change in battery capacity over time for Examples 1-1 to 1-3, Figure 3 shows the change in battery capacity over time for Examples 2-1 to 2-3, and Figure 4 shows the change in battery capacity over time for Comparative Examples 1 to 3. Comparing Figures 2 to 4, the battery capacity in Comparative Examples 1 to 3 (Figure 4) changed unstably over the first 30 cycles or so, whereas the battery capacity in Examples 1-1 to 1-3 (Figure 2) and Examples 2-1 to 2-3 (Figure 3) changed relatively smoothly. While the present invention is not bound by the following speculated mechanism, it is speculated that the charge-discharge characteristics of the battery in Comparative Examples 1 to 3 become unstable due to gas generation accompanying the incorporation and desorption of lithium or chemical reactions between the lithium transition metal oxide and the electrolyte. It is known that positive electrode active materials with a high Ni content are particularly prone to gas generation and unstable cycle operation. In contrast, in each example in which an iodine-containing raw material was added, as described above, the iodine-containing material improved the Li conductivity and promoted the redox reaction of the positive electrode active material during charging, thereby suppressing side reactions and preventing an increase in the positive electrode resistance, resulting in stable long-term cycling. Furthermore, it is presumed that the particle surface of the active material was at least partially coated with the iodine-containing material, thereby suppressing the gas generation reaction between the active material and the electrolyte, thereby achieving stable cycling characteristics.

[0109] [Evaluation Example 5-1: DC resistance (DCR) increase rate due to repeated charging and discharging] For the mono-cell batteries manufactured in Examples 1-1 to 1-3, Examples 2-1 to 2-3, and Comparative Examples 1 to 3, the direct current resistance (DCR) of each mono-cell battery was measured during the first and 300th charge-discharge cycles in the charge-discharge cycle test in Evaluation Example 4. Specifically, the DCR value was calculated from the slope of a straight line that linearly approximated a discharge curve obtained by measuring voltage values ​​at predetermined intervals for 40 seconds after the start of discharge after the full charge state at the completion of the charge cycle. The DCR increase rate before and after the 300-cycle charge-discharge cycle was then calculated from these measurements using the following formula:

number

[0110] The obtained DCR increase rates are shown in Table 4 below. Note that the DCR increase rates in Table 4 are relative values ​​normalized by dividing the DCR increase rate value of each example by the DCR increase rate value of Comparative Example 1. Compared with Comparative Examples 1 to 3, the DCR increase rates of the batteries in each Example were significantly smaller.

[0111] [Evaluation Example 5-2: Impedance after repeated charging and discharging] For the mono-cell batteries produced in Examples 1-1 to 1-3, Examples 2-1 to 2-3, and Comparative Example 1, the impedance of the mono-cell batteries was measured using an impedance analyzer after the 299th charging cycle in the charge-discharge cycle test in Evaluation Example 4 was completed. The impedance (Ω) of the positive electrode was calculated from the positive electrode impedance component that appeared on the low frequency side (100 Hz to 0.01 Hz) in the obtained Cole-Cole plot.

[0112] The obtained impedance values ​​are shown in Table 4 below. However, the impedance values ​​in Table 4 are relative values ​​normalized by dividing the impedance value of each example by the impedance value of Comparative Example 1. Compared to Comparative Example 1, the impedance values ​​of the positive electrode in each example were significantly smaller.

[0113] [Evaluation Example 5-3: Change in battery volume before and after repeated charging and discharging] For the mono-cell batteries manufactured in Example 1-1, Example 2-1, and Comparative Example 1, the volumes of the mono-cell batteries were measured by Archimedes' method at the completion of the first charging cycle and at the completion of the 300th charging cycle in the charge-discharge cycle test in Evaluation Example 4. Next, the volume change of the mono-cell battery before and after 300 cycles of repeated charge and discharge was calculated, which is defined as (volume of battery at the completion of the 300th charging cycle) - (volume of battery at the completion of the first charging cycle).

[0114] The volume change values ​​of the obtained batteries are shown in Table 4 below. Note that the volume change values ​​in Table 4 are relative values ​​normalized by dividing the volume change value of each example by the volume change value of Comparative Example 1. An increase in battery volume was observed in all examples, but the degree of volume change in each example was significantly smaller than in Comparative Example 1. [Table 4]

[0115] In general, repeated charge and discharge of a battery tends to increase the resistance of the electrodes and the entire battery due to the influence of side reaction products, etc. In this regard, the results of Evaluation Example 5-1, which examined the DCR increase rate of the battery, showed that the increase in DC resistance of the entire battery was suppressed in the Examples compared to the Comparative Examples. Furthermore, the results of Evaluation Example 5-2, which examined the impedance of the battery at the 299th cycle, suggested that the impedance of the positive electrode in the Examples was much smaller than that in the Comparative Examples, and that the increase in impedance was also significantly suppressed.

[0116] In general, repeated charging and discharging of a battery tends to cause the battery to expand due to the effects of gas generated by side reactions. Regarding this, the results of Evaluation Example 5-3, which examined the volume change of the battery, suggested that the volume change of the battery in the Examples was smaller than that in the Comparative Examples, suggesting that gas generation was suppressed. From these results, it is inferred that the side reactions were suppressed more in the Examples using iodine-containing raw materials than in the Comparative Examples not using iodine-containing raw materials.

[0117] [Evaluation Example 6-1: Change in battery volume before and after high-temperature storage] For the mono-cell batteries manufactured in Example 1-1, Example 2-1, and Comparative Example 1, the volumes of the mono-cell batteries charged to a fully charged state were measured using the Archimedes method, and then the batteries were stored in a thermostatic chamber maintained at 60°C for two weeks. After removing the batteries from the thermostatic chamber, the volumes of the mono-cell batteries were measured again. Next, the volume change of each mono-cell battery before and after high-temperature storage, defined as (volume of battery after high-temperature storage) - (volume of battery before high-temperature storage), was calculated.

[0118] The volume change values ​​of the obtained batteries are shown in Table 5 below. Note that the volume change values ​​in Table 5 are relative values ​​normalized by dividing the volume change value of each example by the volume change value of Comparative Example 1. An increase in battery volume was observed in all examples, but the degree of volume change in each example was significantly smaller than in Comparative Example 1.

[0119] [Evaluation Example 6-2: Remaining discharge capacity ratio after high-temperature storage] The discharge capacity immediately before the high-temperature storage and immediately after removal from the high-temperature storage were measured for the mono-cell batteries manufactured in Example 1-1, Example 2-1, and Comparative Example 1. The remaining discharge capacity ratio of each mono-cell battery after high-temperature storage was then calculated according to the following formula.

number

[0120] The remaining discharge capacity ratios of the obtained batteries are shown in Table 5 below. Note that the remaining discharge capacity ratio values ​​in Table 5 are relative values ​​normalized by dividing the remaining discharge capacity ratio value of each example by the remaining discharge capacity ratio value of Comparative Example 1. In all examples, the discharge capacity immediately after high-temperature storage was smaller than the discharge capacity immediately before high-temperature storage, but the remaining discharge capacity ratio of Comparative Example 1 was the smallest, and the remaining discharge capacity ratios of Example 1-1 and Example 2-1 were larger than those of Comparative Example 1. In other words, the deterioration of capacity characteristics due to high-temperature storage was suppressed in each example compared to Comparative Example 1.

[0121] [Evaluation Example 6-3: Recovery discharge capacity ratio after high temperature storage] The mono-cell batteries manufactured in Examples 1-1, 2-1, and Comparative Example 1 were removed from the high-temperature storage, discharged once, and then charged again to measure the discharge capacity. The recovered discharge capacity ratio of each mono-cell battery after high-temperature storage was then calculated according to the following formula.

number

[0122] The recovery discharge capacity ratios of the obtained batteries are shown in Table 5 below. Note that the recovery discharge capacity ratio values ​​in Table 5 are relative values ​​normalized by dividing the recovery discharge capacity ratio value of each example by the recovery discharge capacity ratio value of Comparative Example 1. In all examples, the discharge capacity after recharge was smaller than the discharge capacity immediately before high-temperature storage, but the recovery discharge capacity ratio of Comparative Example 1 was the smallest, and the recovery discharge capacity ratios of Examples 1-1 and 2-1 were larger than those of Comparative Example 1. In other words, compared to Comparative Example 1, the deterioration of capacity characteristics due to high-temperature storage was suppressed in each example.

[0123] [Table 5]

[0124] As described above, the remaining capacity and recovered capacity were increased in the examples using the iodine-containing raw material compared to the comparative examples not using the iodine-containing raw material. This suggests that the coating with the iodine-containing material suppresses self-discharge at high temperatures and deterioration of the active material in a charged state during high-temperature storage, and further suppresses expansion of the battery due to high-temperature storage.

[0125] [Reference example 1] Figure 5 shows the I3d of the fired product obtained by mixing orthoperiodic acid H5IO6 as a coating material with lithium transition metal oxide and firing it at 350°C for 5 hours. 2 / 55 shows the XPS spectrum of Example 1-1. Figure 5 confirms that when H5IO6 is used as the iodine-based coating material, a spectrum similar to that of Example 1-1, in which elemental iodine was used as the iodine-based coating material, is obtained. Note that orthoperiodic acid (H5IO6) melts at 132°C, and then dehydration begins, producing metaperiodic acid (HIO4). Furthermore, iodine (V) oxides such as I2O4 and I2O5 decompose into oxygen and iodine at temperatures above 275°C. Based on these findings, it is inferred that regardless of the valence of iodine in the coating raw material (i.e., even when metaperiodic acid (HIO4), I2O4, I2O5, etc. are used as the coating raw material), the oxidation state of iodine after mixing with a lithium transition metal oxide and firing will be similar to that of Example 1-1, in which elemental iodine was used.

Claims

1. a lithium transition metal oxide; an iodine-containing material containing iodine having an oxidation state of +3 or more and +7 or less, which at least partially coats the lithium transition metal oxide particles; Including, A positive electrode active material for a lithium ion secondary battery, wherein the content of the iodine-containing material in the positive electrode active material is 0.001% by weight or more and 10.0% by weight or less.

2. The positive electrode active material according to claim 1 , wherein the iodine-containing material contains iodine having an oxidation number of +5 or more and +7 or less.

3. The positive electrode active material according to claim 1 or 2, wherein the iodine-containing material contains iodine having an oxidation number of +7.

4. The positive electrode active material according to claim 1 , wherein the iodine-containing material contains periodate ions or hydrogen periodate ions.

5. The iodine-containing material contains periodate ions, IO ４ － The positive electrode active material according to any one of claims 1 to 4, comprising:

6. I3d observed by X-ray photoelectron spectroscopy of the positive electrode active material ５／２ The positive electrode active material according to any one of claims 1 to 5, wherein the spectrum of

7. A positive electrode active material slurry for a lithium ion secondary battery, comprising the positive electrode active material according to any one of claims 1 to 6.

8. A positive electrode for a lithium ion secondary battery, comprising a positive electrode active material layer comprising the positive electrode active material according to any one of claims 1 to 6 formed on a current collector.

9. A lithium ion secondary battery comprising the positive electrode according to claim 8.

10. a mixing step of mixing a lithium transition metal oxide and an iodine-containing raw material in a solid state to prepare an iodine-containing mixture; a calcination step of calcining the iodine-containing mixture; The method for producing the positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 6, comprising:

11. The iodine-containing raw material is elemental iodine (I ２ ), lithium iodide (LiI), sodium iodide (NaI), potassium iodide (KI), iodoform (CHI ３ ), carbon tetraiodide (CI ４ ), ammonium iodide (NH ４ Iodic acid (HIO ３ ), lithium iodate (LiIO ３ ), sodium iodate (NaIO ３ ), potassium iodate (KIO ３ ), ammonium iodate (NH ４ IO ３ ), metaperiodic acid (HIO ４ ), orthoperiodic acid (H ５ IO ６ ), lithium periodate (LiIO ４ ), sodium periodate (NaIO ４ ), potassium periodate (KIO ４ ), iodine (IV) oxide (I ２ O ４ ), iodine(V) oxide (I ２ O ５ ), and iodine (IV, V) oxide (I ４ O ９ The method for producing a positive electrode active material according to claim 10 , comprising at least one selected from the group consisting of:

12. The iodine-containing raw material is elemental iodine (I ２ The method for producing a positive electrode active material according to claim 10 or 11, comprising:

13. The method for producing a positive electrode active material according to any one of claims 10 to 12, wherein the iodine-containing raw material is mixed with the lithium transition metal oxide so as to be 0.01% by weight or more and 5% by weight or less with respect to the lithium transition metal oxide.

14. The method for producing a positive electrode active material according to any one of claims 10 to 13, wherein the firing step is carried out in air.

15. The method for producing a positive electrode active material according to any one of claims 10 to 14, wherein the firing step includes a step of firing the iodine-containing mixture at a firing temperature of 150°C or higher and 500°C or lower.

16. The method for producing a positive electrode active material according to claim 15, wherein in the baking step, a baking time during which the iodine-containing mixture is maintained at the baking temperature is from 1 hour to 12 hours.

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