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 positive electrode active material for a lithium-ion secondary battery that is excellent in capacity characteristics and electrode resistance characteristics, and to provide a positive electrode active material slurry, a positive electrode, a lithium-ion secondary battery, and a method of manufacturing a positive electrode active material.SOLUTION: A positive electrode active material includes: a core containing lithium transition metal oxide; and a coating part at least partially covering a surface of the core, containing iodine and boron.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] To increase the capacity of such lithium ion secondary batteries, a known technique is to form a coating made of, for example, a boron material on the surface of an electrode active material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6284542 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-152275 [Patent Document 3] Japanese Patent Application Publication No. 2019-175872 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when such a coating is formed, there are cases where sufficient electrode resistance characteristics cannot be obtained, and therefore it is desired to achieve both excellent capacitance characteristics and excellent electrode resistance characteristics.

[0006] The problem to be solved by the present invention is to provide a positive electrode active material for a lithium ion secondary battery, which has excellent capacity characteristics and electrode resistance characteristics, a positive electrode active material slurry, a positive electrode, a lithium ion secondary battery, and a method for producing the positive electrode active material. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a positive electrode active material including a core including a lithium transition metal oxide and a coating portion that at least partially covers the surface of the core, the coating portion including iodine and boron.

[0008] 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 other than oxygen, such as iodine. "Coating" refers to at least partially covering the surface of an object, and includes both chemical bonding to the particle surface and physical coating without chemical bonding. For example, if peaks derived from iodine and boron are detected in X-ray photoelectron spectroscopy (XPS) of the particle surface of an active material, it can be said that "a coating containing iodine and boron is formed."

[0009] In the positive electrode active material according to the above embodiment, the coating portion may contain iodine having an oxidation number of +5 or more and +7 or less.

[0010] In the positive electrode active material according to the above embodiment, I3d observed by X-ray photoelectron spectroscopy of the positive electrode active material 5 / 2 The spectrum may have a peak between 622 eV and 626 eV.

[0011] In the positive electrode active material according to the above embodiment, the content of iodine may be 0.001 to 5 parts by mass relative to 100 parts by mass of the lithium transition metal oxide.

[0012] In the positive electrode active material according to the above embodiment, the content of boron can be 0.001 to 5 parts by mass relative to 100 parts by mass of the lithium transition metal oxide.

[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] In the positive electrode according to the above aspect, the positive electrode active material layer may further contain a conductive agent containing carbon nanotubes.

[0016] 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.

[0017] According to another aspect of the present invention, there is provided a method for producing a cathode active material, the method comprising obtaining a mixture including a lithium transition metal oxide, iodine, and boron, and calcining the mixture.

[0018] The method for producing a positive electrode active material according to the above aspect can include adding an iodine material containing iodine as a raw material of the mixture. The iodine material may include one or more selected from the group consisting of elemental iodine (I), lithium iodide (LiI), sodium iodide (NaI), potassium iodide (KI), iodoform (CHI), carbon tetraiodide (CI), ammonium iodide (NHI), iodic acid (HIO), lithium iodate (LiIO), sodium iodate (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). As used herein, "iodine material" means any material that contains iodine.

[0019] In the method for producing a positive electrode active material according to the above embodiment, the iodine material may include elemental iodine (I2).

[0020] The method for producing a positive electrode active material according to the above embodiment may include adding a boron material containing boron as a raw material of the mixture. The boron material may be H3BO3, HBO2, B2O3, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, C 13 H 19 The material may include one or more selected from the group consisting of BO3, C3H9B3O6, and (C3H7O)3B. As used herein, the term "boron material" refers to any material that contains boron.

[0021] In the method for producing a positive electrode active material according to the above embodiment, the boron material may include boric acid (H3BO3).

[0022] The method for producing a positive electrode active material according to the above embodiment may include firing the mixture at a firing temperature of 150°C or higher and 500°C or lower. [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 capacity characteristics and electrode resistance characteristics, a positive electrode active material slurry, a positive electrode, a lithium ion secondary battery, and a method for producing a 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, Comparative Example 1-1, Comparative Example 2-1, and Comparative Example 3-1. [Figure 2] 1 shows a portion of the XPS spectra of the positive electrode active materials of Example 1-1, Comparative Example 1-1, Comparative Example 2-1, and Comparative Example 3-1. [Figure 3] 1 shows the progress of changes in battery capacity during the 1st to 50th charge / discharge processes in Examples 1-1 and 2, and Comparative Examples 1-1, 2-1, 3-1, and 4. [Figure 4] 1 shows the transition of DC resistance change in the 1st to 200th charge / discharge processes of Example 1-1, Example 2, Comparative Example 1-1, Comparative Example 2-1, Comparative Example 3-1, and Comparative Example 4. [Figure 5] 1 shows the progress of changes in battery capacity during the 1st to 50th charge / discharge processes in Example 1-2, Comparative Example 1-2, Comparative Example 2-2, and Comparative Example 3-2. [Figure 6] 1 shows the transition of DC resistance change during the 1st to 200th charge / discharge processes in Example 1-2, Comparative Example 1-2, Comparative Example 2-2, and Comparative Example 3-2. [Figure 7] 1 shows a portion of the XPS spectrum of the positive electrode active material of Reference Example 1. 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 electrode resistance characteristics that may arise as the capacity of lithium-ion secondary batteries increases will be explained by taking 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 z It 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 mass 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, a method for forming a coating on the particle surface of positive electrode active material has been proposed to suppress gas generation and achieve stable cycle behavior. However, Ni-rich positive electrodes with a high Ni content are significantly affected by the increase in resistance components caused by such coating treatment. Depending on the treatment, not only can the discharge capacity and rate characteristics decrease, but the cycle characteristics may also deteriorate. In this regard, as described in Patent Documents 1 and 2, techniques for forming boron-based coatings are known, but their effectiveness for Ni-rich positive electrodes is limited. Meanwhile, as described in Patent Document 3, the formation of an additional coating in addition to the boron-based coating has also been considered. However, the increase in electrode resistance due to the overlapping of coatings can also be a practical issue. As such, currently, there are very few coating technologies that can achieve both excellent capacity and electrode resistance characteristics for active materials currently in use or under development.

[0029] The present inventors have discovered that when a positive electrode active material containing a lithium transition metal oxide is used in a lithium ion secondary battery, a lithium ion secondary battery having both excellent capacity characteristics and electrode resistance characteristics can be obtained by forming a coating portion containing iodine and boron on the surface of a core containing a lithium transition metal oxide, and have completed the present invention.

[0030] [Cathode active material] According to one embodiment, there is provided a positive electrode active material including a core containing a lithium transition metal oxide and a coating portion at least partially coating the surface of the core, the coating portion including iodine and boron. Preferably, the positive electrode active material is a positive electrode active material for a lithium ion secondary battery.

[0031] The positive electrode active material may contain a lithium transition metal oxide capable of absorbing and releasing lithium, iodine, and boron. The positive electrode active material may be in the form of particles having a core-shell structure formed from a core and a coating. The coating may surround the entire core, or may cover only a portion of the outer surface of the core. The coating may be continuous as a whole, or may have multiple island-like portions separated from each other. The coating may coat a single core, or may coat two or more cores.

[0032] (core) The core of the positive electrode active material contains a lithium transition metal oxide. For example, the core is a particle of lithium transition metal oxide. The core may contain a material other than lithium transition metal oxide. The shape of the core is not particularly limited and may be any shape, such as a sphere, a rectangular parallelepiped, or a polygon, and the particle form is also not limited. For example, the core may be formed from a single particle or from an aggregate of secondary particles formed by aggregation of primary particles. The size of the core is not particularly limited and may be, for example, from 0.01 μm to 30 μm, or from 0.1 μm to 10 μm.

[0033] The core of the positive electrode active material includes, for example, a lithium transition metal oxide containing nickel, and preferably may include a lithium transition metal oxide having a high nickel content. Here, "having a high nickel content" means containing 50 mol% or more of nickel based on the total amount of transition metals. As described above, it is desirable to suppress an increase in electrode resistance for a high-nickel lithium transition metal oxide containing 50 mol% or more of nickel. For this reason, by improving the electrode resistance characteristics (that is, reducing the rate of increase in resistance) using the positive electrode active material according to the present embodiment, it becomes possible to achieve both a higher capacity and improved electrode resistance characteristics of the lithium ion secondary battery. For example, the core 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.

[0034] (Lithium transition metal oxide) Examples of the lithium transition metal oxide include lithium-manganese-based oxides (for example, LiMnO2, LiMnO3, LiMn2O3, LiMn2O4, etc.); lithium-cobalt-based oxides (for example, LiCoO2, etc.); lithium-nickel-based oxides (for example, LiNiO2, etc.); lithium-copper-based oxides (for example, Li2CuO2, etc.); lithium-vanadium-based oxides (for example, LiV3O8, etc.); lithium-nickel-manganese-based oxides (for example, LiNi 1-z Mn z O2 (0 < z < 1), LiMn 2-z Ni z O4 (0 < z < 2), etc.); lithium-nickel-cobalt-based oxides (for example, LiNi 1-y Co y O2 (0 < y < 1), etc.); lithium-manganese-cobalt-based oxides (for example, 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 (for example, Li(Ni x Co y Mn z)O2(0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1), Li(Ni x Co y Mn z )O4(0 < x < 2, 0 < y < 2, 0 < z < 2, x + y + z = 2), etc.); lithium-nickel-cobalt-metal (M) oxide (e.g., Li(Ni x Co y Mn z M w )O2 (M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, 0 < x < 1, 0 < y < 1, 0 < z < 1, 0 < w < 1, x + y + z + w = 1), etc.); Li-excess solid solution cathode (e.g., pLi2MnO3-(1-p)Li(Ni x Co y Mn z )O2 (0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1, 0 < p < 1); compounds in which the transition metal elements in these compounds are partially substituted by one or two or more other metal elements, etc. The cathode active material layer can contain any one or two or more of these compounds, but is not limited thereto.

[0035] In particular, as examples of lithium transition metal oxides with a high nickel content effective for increasing the battery capacity, 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 (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 )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 a part of the transition metal atoms in these compounds 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 the 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. are included. 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, the surface coated with a metal oxide, a lithium transition metal oxide, a polymer, etc. can be mentioned, but is not limited thereto.

[0036] Particularly, 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 Mn y Co z )O2 (y + z = 0.2), Li a (Ni 0.8 Co y [[ID=第43]]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 It should be noted that there is a misspelling in the original text where "第43" should be "Mn" which has been corrected in the translation.)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.

[0037] 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.

[0038] (Covered part) The coating portion of the positive electrode active material coats part or all of the surface of the core. The coating portion contains iodine and boron. The coating portion is obtained by mixing and baking a lithium transition metal oxide, an iodine material, and a boron material. The coating portion in the positive electrode active material may exist independently of the core containing the lithium transition metal oxide, or may be chemically or physically bonded at least partially to the surface of the lithium transition metal oxide particle that forms the core. The coating portion is preferably at least partially in contact with the lithium transition metal oxide particle. The coating portion may be at least partially included in the structure of the lithium transition metal oxide. Note that the material of the coating portion is not limited to an independent chemical species as a compound, and may be any chemical species such as an ion, atom, or atomic group. The thickness of the coating portion is not particularly limited, but a thickness of 0.1 nm to 10 nm is preferable, and a thickness of 3 nm to 5 nm is even more preferable, because complete coating or a thick coating layer inhibits the electrical conductivity of the core surface. In addition, using carbon nanotubes or the like to electrically connect particles is also effective in suppressing a decrease in electrical conductivity.

[0039] The content of the coating portion in the positive electrode active material is, for example, 0.001% by mass or more and 10.0% by mass or less, preferably 0.01% by mass or more and 1.0% by mass or less, more preferably 0.02% by mass or more and 0.5% by mass or less, and even more preferably 0.05% by mass or more and 0.2% by mass or less. If the content of the coating portion is 0.001% by mass or more, improvements in the cycle characteristics and electrode resistance characteristics of the battery can be expected.

[0040] (Iodine component) The coating portion in the positive electrode active material after firing contains iodine having a positive oxidation number. The coating portion contains, for example, iodine having an oxidation number of +1 or more and +7 or less, preferably iodine having an oxidation number of +2 or more and +7 or less, more preferably iodine having an oxidation number of +5 or more and +7 or less, and even more preferably iodine having an oxidation number of +7. Iodine having a positive oxidation number often has strong oxidizing power. For example, iodine compounds having a positive oxidation state include iodine oxoacids such as iodic acid (HIO), metaperiodic acid (HIO), and orthoperiodic acid (HIO); iodine oxoacid salts such as lithium iodate (LiIO), sodium iodate (NaIO), potassium iodate (KIO), ammonium iodate (NHIO), lithium periodate (LiIO), sodium periodate (NaIO), and potassium periodate (KIO); and iodine oxides such as iodine(IV) oxide (IO), iodine(V) oxide (IO), and iodine(IV,V) oxide (IO). The coating may contain periodate ions or hydrogen periodate ions. Examples of periodate ions include metaperiodate ions, IO, and - , orthoperiodate ion IO6 5- The hydrogen periodate ion is HIO6 4- , H2IO6 3- , H3IO6 2- , H4IO6 - The iodine contained in the coating portion may be bonded to the constituent elements (lithium, transition metal, oxygen, etc.) of the lithium transition metal oxide or to iodine. For example, the coating portion may contain iodate ions IO3 bonded to the metal ions of the lithium transition metal oxide. - Alternatively, the coating may contain periodate ions. For example, the coating may contain a bond between a metal cation such as a lithium transition metal oxide and a periodate ion, for example, a bond between the metal cation and the periodate ion IO4 - It may include bonding with

[0041] In the positive electrode active material, the iodine content relative to 100 parts by mass of lithium transition metal oxide is, for example, 0.001 to 5 parts by mass. If the iodine content is 0.001 part by mass or more, improvements in the electrode resistance characteristics and cycle characteristics of the battery are expected. If the iodine content is 5 parts by mass or less, it is believed that side reactions due to excessive coating are suppressed. The iodine content relative to 100 parts by mass of lithium transition metal oxide is preferably 0.005 to 2 parts by mass, more preferably 0.01 to 1 part by mass, and even more preferably 0.05 to 0.5 parts by mass.

[0042] (boron component) The coating portion in the positive electrode active material after firing contains boron having an oxidation number of +3. Examples of boron compounds contained in the coating portion include boric acid, borate salts, polyboric acid, polyboric acid salts, and boron oxide. The boron contained in the coating portion may be bonded to a constituent element (lithium, transition metal, oxygen, etc.) of the lithium transition metal oxide or to iodine. For example, the coating portion may contain borate ions (referred to herein as BO3) bonded to metal ions of the lithium transition metal oxide. 3- , HBO3 2- , H2BO3 - are collectively referred to as "borate ions." For example, the coating may include a bond between a metal cation such as a lithium transition metal oxide and a borate ion. For example, the coating may include lithium metaborate (LiBO2). Patent Document 1 also proposes that boric acid reacts with residual lithium to form lithium borate.

[0043] In the positive electrode active material, the content of boron relative to 100 parts by mass of lithium transition metal oxide is, for example, 0.001 to 5 parts by mass. If the content of boron is 0.001 part by mass or more, improvements in the capacity characteristics and cycle characteristics of the battery are expected. If the content of boron is 5 parts by mass or less, it is believed that side reactions due to excessive coating are suppressed. The content of boron relative to 100 parts by mass of lithium transition metal oxide is preferably 0.01 to 3 parts by mass, more preferably 0.05 to 2 parts by mass, and even more preferably 0.1 to 1 part by mass.

[0044] (XPS spectrum of positive electrode active material) The spectrum observed by X-ray photoelectron spectroscopy (XPS) of the positive electrode active material is 5 / 2 It has a peak due to electrons. -(CH2) n When the charge correction is performed with the energy of the C1s peak top derived from the I3d 5 / 2 The spectrum of has a peak, for example, between 622 eV and 626 eV. The position of the peak is preferably between 623 eV and 625 eV, more preferably between 623.5 eV and 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 a positive oxidation number. This peak is derived from iodine having an oxidation number of +1 or more and +7 or less, preferably from iodine having an oxidation number of +3 or more and +7 or less, more preferably from iodine having an oxidation number of +5 or more and +7 or less, and even more preferably from iodine having an oxidation number of +7.

[0045] The spectrum observed by X-ray photoelectron spectroscopy (XPS) of the positive electrode active material has a peak due to the B1s electron of boron. n When charge correction is performed with the energy of the C1s peak top of the boron-derived fluorine atom set to 284.6 eV, the spectrum of the B1s electrons of boron has a peak, for example, between 188.5 eV and 195.0 eV.

[0046] It is speculated that the coating portion can improve the capacity characteristics and electrode resistance characteristics of the battery and suppress cycle deterioration through the following mechanism: However, the following is merely an exemplary speculation to aid in understanding the invention and does not limit the present invention in any way.

[0047] When a lithium transition metal oxide, an iodine material, and a boron material are mixed and sintered, the iodine and boron materials are thought to undergo a chemical reaction, either individually or in concert, on the lithium transition metal oxide, forming a coating containing iodine and boron. While the function of the coating in the positive electrode active material is also unclear, the coating thus formed may contain iodine, which has a positive oxidation state and strong electron-withdrawing properties, as described above. Previous research has 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 coating improves Li conductivity and promotes the redox reaction of the positive electrode active material during charging. As a result, side reactions such as electrolyte decomposition during charging are suppressed, suppressing the increase in electrode resistance on the positive electrode side, resulting in stable, long-term cycling.

[0048] The resulting coating is thought to at least partially coat the surface of the core containing the lithium transition metal oxide. This coating suppresses the chemical reaction between the lithium transition metal oxide 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 cycles and an increase in the battery's electrical resistance.

[0049] As will be shown in the examples below, the formation of a boron-derived coating tended to increase electrode resistance, but it was also confirmed that the inclusion of iodine in the coating portion tended to suppress the increase in electrode resistance. This action of iodine can suppress the increase in electrode resistance due to the coating portion while realizing the effect of improving and stabilizing battery performance due to the coating portion. It is not clear whether the boron-containing coating and the iodine-containing coating are formed separately and function independently, or whether some kind of interaction occurs between boron and iodine.

[0050] Lithium transition metal oxides with a high nickel content, in particular, tend to be significantly affected by increased electrode resistance. While insulating metal oxide coatings such as Al2O3 are generally effective for lithium cobalt oxides, Ni-containing layered oxides often experience increased surface resistance due to the metal oxides, resulting in increased electrode resistance and insufficient battery performance. On the other hand, boron coatings have a smaller effect on surface resistance than metal oxides, and are known to be effective even for Ni-containing layered oxide materials. However, high-nickel lithium transition metal oxides can be affected by even a slight increase in resistance due to boron, resulting in insufficient battery performance. In this regard, forming a coating containing boron and iodine as described above can achieve both improved capacity and electrode resistance, even when using high-nickel lithium transition metal oxides, which are susceptible to electrode resistance. Generally, batteries using high-nickel lithium transition metal oxides tend to have higher capacities, which is advantageous in terms of increasing battery capacity.

[0051] [Method of manufacturing positive electrode active material] According to one embodiment, there is provided a method for producing a cathode active material, the method comprising obtaining a mixture including a lithium transition metal oxide, iodine, and boron, and calcining the obtained mixture.

[0052] (1)Mixture In the mixing process, at least one lithium transition metal oxide, an iodine material, and a boron material are mixed. For example, in the mixing process, the lithium transition metal oxide, the iodine material, and the boron material may all be mixed in a solid state. For example, a powdered mixture can be obtained by mixing powdered lithium transition metal oxide, iodine material, and boron material. Hereinafter, the resulting mixture is referred to as a "pre-calcination mixture." The specific mixing method is not particularly limited, and any known method can be used. The mixing step may be performed in air or in another atmosphere, such as an inert atmosphere. In addition, optional materials may be added in addition to the lithium transition metal oxide, iodine material, and boron material. Mixing the raw materials in a solid state simplifies the mixing process, reduces costs, and is suitable for mass production.

[0053] (Iodine materials) The iodine material is a raw material for introducing iodine into the positive electrode active material, and is preferably an iodine material that is solid at room temperature, since it can be easily mixed with the lithium transition metal oxide. For example, the iodine material may include one or more 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 (KIO3), ammonium iodate (NH4IO3), metaperiodic acid (HIO4), orthoperiodic acid (H5IO6), lithium periodate (LiIO4), sodium periodate (NaIO4), potassium periodate (KIO4), iodine(IV) oxide (IO4), iodine(V) oxide (IO5), and iodine(IV,V) oxide (IO9). In addition, any iodine material can be used, such as metal iodide or an iodine-containing organic compound, as long as it does not have a significant adverse effect on the battery characteristics. The valence of iodine in the iodine material is not particularly limited.

[0054] (Boron materials) The boron material is a raw material for introducing boron into the positive electrode active material. The boron material is preferably a solid at room temperature, since it can be easily mixed with a lithium transition metal oxide. For example, the boron material may be H3BO3, HBO2, B2O3, LiBO2, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, C 13 H 19 The boron material may include one or more selected from the group consisting of BO3, C3H9B3O6, and (C3H7O)3B. Any boron material, such as a metal boride, may be used as long as it does not significantly adversely affect the battery characteristics. The valence of boron in the boron material is not particularly limited.

[0055] The amount of lithium transition metal oxide added in the mixing process is, for example, 85 parts by mass or more and 99.98 parts by mass or less, preferably 90 parts by mass or more and 99.9 parts by mass or less, and more preferably 95 parts by mass or more and 99.5 parts by mass or less, assuming the total mass of the pre-calcination mixture to be 100 parts by mass.

[0056] The amount of the iodine material added is, for example, 0.001 to 5 parts by mass, preferably 0.01 to 4 parts by mass, more preferably 0.05 to 3 parts by mass, and even more preferably 0.1 to 2 parts by mass. If the amount of the iodine material added is 0.001 parts by mass or more, improvements in the electrode resistance characteristics and cycle characteristics of the battery are expected. If the amount of the iodine material added is 5 parts by mass or less, excessive side reactions are thought to be suppressed.

[0057] The amount of boron material added is, for example, 0.01 to 5 parts by mass, preferably 0.05 to 4 parts by mass, more preferably 0.1 to 3 parts by mass, and even more preferably 0.5 to 2 parts by mass. If the amount of boron material added is 0.01 parts by mass or more, improvements in the capacity characteristics and cycle characteristics of the battery are expected. If the amount of boron material added is 5 parts by mass or less, excessive side reactions are thought to be suppressed.

[0058] (2) Firing In the calcination process, the pre-calcination mixture obtained in the mixing process is calcined to obtain a positive electrode active material. Calcination is preferably performed in the presence of oxygen, more preferably in the atmosphere, but may be performed in other atmospheres. For example, calcination may be performed in an inert atmosphere such as a nitrogen atmosphere or a rare gas atmosphere such as argon. Calcination performed in the atmosphere simplifies the calcination step, reduces costs, and is suitable for mass production.

[0059] The firing temperature for firing the 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 between the iodine material and the boron material. Furthermore, a firing temperature of 500°C or lower is thought to suppress the formation of excessive by-reaction products. Furthermore, the firing temperature for firing the mixture is preferably equal to or higher than the melting points of the iodine material and the boron material, more preferably equal to or higher than the boiling points of the iodine material and the boron material.

[0060] The calcination time during which the 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 material and the boron material to react to the required extent. Furthermore, a calcination time of 12 hours or less can reduce costs by avoiding excessively long calcination times.

[0061] [Positive electrode active material slurry] According to one embodiment, there is provided a positive electrode active material slurry for a lithium ion secondary battery, the positive electrode active material slurry including, for example, the positive electrode active material, a conductive agent, a binder, and a solvent.

[0062] The content of the positive electrode active material in the positive electrode active material layer may be 80% by mass or more and 99.5% by mass or less, based on the total mass of the positive electrode active material layer. The content of the positive electrode active material may preferably be 85% by mass or more and 98.5% by mass or less. When the content of the positive electrode active material is within the above range, excellent capacity characteristics can be achieved. 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 agent may be insufficient, resulting in insufficient electrode conductivity and adhesive strength, which may lead to reduced battery performance.

[0063] (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.

[0064] As will be shown in the examples below, the use of carbon nanotubes as a conductive agent can significantly reduce the impedance of the electrode, so it is preferable that the positive electrode active material slurry contains carbon nanotubes.

[0065] The content of the conductive agent may be 0.1% by mass or more and 30% by mass or less, based on the total mass of the positive electrode active material layer. The content of the conductive agent may be preferably 0.5% by mass or more and 15% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less. When the content of the conductive agent satisfies the above range, sufficient conductivity can be imparted and the amount of the positive electrode active material is not reduced, which is advantageous in that battery capacity can be ensured.

[0066] (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.

[0067] The binder content may be 0.1% by mass or more and 30% by mass or less, based on the total mass of the positive electrode active material layer. The binder content may be preferably 0.5% by mass or more and 15% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less. 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.

[0068] (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.

[0069] The amount of solvent used is sufficient as long as it has a viscosity that allows the positive electrode active material, conductive agent, 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.

[0070] [Method for producing positive electrode active material slurry] The positive electrode active material slurry can be obtained by adding and mixing the above-mentioned positive electrode active material with a conductive agent, a binder, a solvent, etc. If necessary, other additives such as a dispersant or a thickener may be added.

[0071] [Positive electrode] According to one embodiment, a positive electrode for a lithium ion secondary battery is provided, in which a positive electrode active material layer containing the above-described positive electrode active material is formed on a current collector. That is, 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 is a positive electrode for a lithium ion secondary battery containing an electrolyte solution.

[0072] (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.

[0073] 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.

[0074] (Cathode active material layer) The positive electrode active material layer includes the above-described positive electrode active material, a conductive agent, and a binder. The positive electrode active material layer may have a thickness of, for example, 1 nm to 100 μm, 10 nm to 10 μm, or 100 nm to 1 μm. The positive electrode active material layer may be formed directly on the positive electrode current collector, or may be formed with another layer sandwiched therebetween. Furthermore, another layer, such as a protective film, may be further formed on the positive electrode active material layer.

[0075] The positive electrode active material layer may contain a conductive agent containing carbon nanotubes, which can significantly reduce the impedance of the electrode and improve the electrode resistance characteristics.

[0076] [Cathode manufacturing method] 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.

[0077] 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.

[0078] [Lithium-ion secondary battery] According to one embodiment, a lithium-ion secondary battery is provided that includes the above-described positive electrode. For example, the lithium-ion secondary battery includes the above-described positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. Note that if a solid electrolyte is used as the non-aqueous electrolyte, the separator may be omitted. The lithium-ion secondary battery may optionally include a battery case that houses an electrode assembly composed of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery case.

[0079] [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.

[0080] (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.

[0081] 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.

[0082] (Negative electrode active material layer) The negative electrode active material layer includes a negative electrode active material, a binder, and a conductive agent. The negative electrode active material layer may have a thickness of, for example, 1 nm to 100 μm, 10 nm to 10 μm, or 100 nm to 1 μm. The negative electrode active material layer may be formed directly on the negative electrode current collector, or may be formed with another layer sandwiched therebetween. Furthermore, another layer, such as a protective film, may be further formed on the negative electrode active material layer.

[0083] 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.

[0084] (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.

[0085] The negative electrode active material may be contained in an amount of 80% by mass or more and 99% by mass or less based on the total mass of the negative electrode active material layer.

[0086] (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.

[0087] (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.

[0088] [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.

[0089] [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.

[0090] [Non-aqueous electrolyte] In the lithium ion secondary battery according to the embodiment, the non-aqueous electrolyte may be, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, or the like that can be used in the manufacture of a lithium ion secondary battery. For example, a solid electrolyte may also be used.

[0091] 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."

[0092] 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.

[0093] 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.

[0094] 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% by mass to 15% by mass based on the total mass of the electrolyte.

[0095] [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.

[0096] 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.

[0097] 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]

[0098] 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.

[0099] [Example 1-1] (Addition of iodine and boric acid) LiNi 0.90 Co 0.07 Mn 0.03To 100 parts by mass of O2 (hereinafter also referred to as "lithium transition metal oxide") powder, 1.0 part by mass of elemental iodine (I2; Fujifilm Wako Pure Chemical Industries, Ltd.) powder and 0.3 part by mass of boric acid (H3BO3; Fujifilm Wako Pure Chemical Industries, Ltd.) were added and sealed in a plastic bottle. The plastic bottle was held in the hand and shaken up and down for about 1 minute to mix the contents, obtaining a mixture.

[0100] (Firing) The resulting mixture was heated to 350° C. in the atmosphere, baked by holding at 350° C. for 5 hours, and cooled to room temperature to obtain a positive electrode active material.

[0101] (Production of Positive Electrode Active Material Slurry) Next, 1.5 parts by mass of carbon black as a conductive material and 2.0 parts by mass of polyvinylidene fluoride (PVDF) as a binder were added to 96.5 parts by mass of the above positive electrode active material, along with N-methyl-2-pyrrolidone (NMP) as a solvent, and mixed to obtain a positive electrode active material slurry.

[0102] (Production of positive electrode sheets) 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.

[0103] (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 mass % of vinylene carbonate (VC) was added to obtain an electrolyte solution.

[0104] (Coin cell battery manufacturing) The resulting positive electrode sheet was punched into a circle with a diameter of 13 mm to obtain a coin cell positive electrode. A CR2016 coin cell battery was fabricated using the resulting positive electrode, a 0.3 mm thick lithium metal negative electrode, and the above electrolyte.

[0105] (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.

[0106] [Example 1-2] A coin cell battery and a mono-cell battery were manufactured in the same manner as in Example 1-1, except that a mixture of 1.5 parts by mass of carbon black and carbon nanotubes was used as the conductive material instead of 1.5 parts by mass of carbon black.

[0107] [Example 2] A coin cell battery and a mono-cell battery were manufactured in the same manner as in Example 1-1, except that the amount of boric acid added was 0.5 parts by mass.

[0108] [Comparative Example 1-1] Coin cell batteries and mono-cell batteries were manufactured in the same manner as in Example 1-1, except that the steps of adding iodine and boric acid and the firing step were omitted. 0.90 Co 0.07 Mn 0.03 O2 was used as the positive electrode active material.

[0109] [Comparative Example 1-2] A coin cell battery and a monocell battery were manufactured in the same manner as in Comparative Example 1-1, except that a mixture of 1.5 parts by mass of carbon black and carbon nanotubes was used as the conductive material instead of 1.5 parts by mass of carbon black.

[0110] [Comparative Example 2-1] A coin cell battery and a mono-cell battery were manufactured in the same manner as in Example 1-1, except that only 1.0 part by mass of iodine was added and no boric acid was added.

[0111] [Comparative Example 2-2] A coin cell battery and a monocell battery were manufactured in the same manner as in Comparative Example 2-1, except that a mixture of 1.5 parts by mass of carbon black and carbon nanotubes was used as the conductive material instead of 1.5 parts by mass of carbon black.

[0112] [Comparative Example 3-1] A coin cell battery and a mono-cell battery were manufactured in the same manner as in Example 1-1, except that only 0.3 parts by mass of boric acid was added and no iodine was added.

[0113] [Comparative Example 3-2] A coin cell battery and a monocell battery were manufactured in the same manner as in Comparative Example 3-1, except that a mixture of 1.5 parts by mass of carbon black and carbon nanotubes was used as the conductive material instead of 1.5 parts by mass of carbon black.

[0114] Comparative Example 4 A coin cell battery and a mono-cell battery were manufactured in the same manner as in Example 1-1, except that only 0.5 parts by mass of boric acid was added and no iodine was added.

[0115] The manufacturing conditions for the above examples and comparative examples are summarized in Table 1. The amounts of the positive electrode active material, conductive agent, and binder added are shown in parts by mass, and the values ​​of the conductive agent and binder are shown in parts by mass relative to 96.5 parts by mass of the positive electrode active material. [Table 1]

[0116] [Evaluation Example 1: 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 Example 1-1 and Example 2 were shown in Table 2 below as the iodine and boron contents of each sample. Note that, since X-ray fluorescence analysis generally has low sensitivity to boron, the boron content values ​​are for reference only. [Table 2]

[0117] [Evaluation Example 2: X-ray photoelectron spectroscopy (XPS) measurement of positive electrode active material] The positive electrode active materials obtained in Example 1-1 and Comparative Example 1-1 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 Charge correction was performed by setting the energy of the C1s peak top derived from - at 284.6 eV.

[0118] 1 shows a portion of the XPS spectrum of the positive electrode active materials of Example 1-1 (solid line) and Comparative Example 1-1 (dotted line). As shown in FIG. 1, the positive electrode active material of Example 1-1 exhibits a 3d peak of iodine in the range of 622 eV to 626 eV, with a peak top near 624 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 is close to the peak positions of sodium iodate (NaIO3) and lithium iodate (LiIO3), which contain iodine with an oxidation state of +5, and sodium periodate (NaIO4) and lithium periodate (LiIO4), which contain iodine with an oxidation state of +7. Therefore, it is presumed that the positive electrode active material contains at least a portion of iodine with a positive oxidation state. More specifically, it is presumed that the iodine in the positive electrode active material is at least a portion of the iodine in the form of iodate ions and / or periodate ions. Note that in Example 1-1, no peaks near 618 eV to 620 eV derived from iodine with an oxidation state of 0 or -1 were observed.

[0119] Regarding boron, as shown in Figure 2, a peak derived from B1s electrons of boron was observed in the range of 195.0 eV to 188.5 eV with a peak top near 191.5 eV in the positive electrode active material of Example 1-1, whereas no peak was observed in the positive electrode active material of Comparative Example 1. The position of this peak is close to the peak position of lithium metaborate (LiBO2). Therefore, it is presumed that the positive electrode active material contains at least a trivalent electron.

[0120] [Evaluation Example 3-1: Initial charge / discharge characteristics] The coin cell batteries manufactured according to each example and comparative example were repeatedly charged and discharged in a thermostatic chamber maintained at 25° C. or 45° C., with a charge upper limit voltage of 4.25 V and a discharge lower limit voltage of 3 V, at a charge current rate of 0.3 C and a discharge current rate of 0.3 C. The charge capacity and discharge capacity in the first charge / discharge process were measured.

[0121] The "initial charge capacity" is defined as the charge capacity in the first charge / discharge process divided by the mass of the positive electrode active material powder, as shown in the following formula. The "initial discharge capacity" is defined as the discharge capacity in the first charge / discharge process divided by the mass of the positive electrode active material powder. The ratio of the discharge capacity to the charge capacity in the first charge / discharge process is defined as the "initial efficiency." From the measured charge capacity and discharge capacity, the initial charge capacity, initial discharge capacity, and initial efficiency at 25°C, as well as the initial discharge capacity at 45°C, were calculated.

number

number

number

[0122] [Evaluation Example 3-2: DC Resistance (DCR) Characteristics] For the coin cell batteries manufactured according to each example and comparative example, the direct current resistance (DCR) was measured at the completion of the first charge cycle and at the completion of the 30th charge cycle. Specifically, the DC resistance was calculated from the slope of a straight line that linearly approximated the discharge curve obtained by measuring voltage values ​​at predetermined intervals for 60 seconds from immediately after the start of discharge after the fully charged state at the completion of the charging process. The DC resistance after the completion of the first charge was defined as the "initial DC resistance." The DC resistance ratio, defined by the following equation, was also calculated.

number

[0123] (Results without adding carbon nanotubes) Table 3 shows the evaluation results of Evaluation Example 3-1 and Evaluation Example 3-2 for Examples 1-1 and 2, and Comparative Examples 1-1, 2-1, 3-1, and 4. Table 3 shows the evaluation results, including the initial charge capacity, initial discharge capacity, and initial efficiency at 25°C, the initial discharge capacity at 45°C, and the initial DC resistance and DC resistance ratio. However, for comparison, Table 3 lists relative values ​​obtained by dividing the actual values ​​by the corresponding values ​​in Comparative Example 1-1. The "Iodine" and "Boric Acid" columns list the values ​​of the parts by mass of iodine and boric acid added per 100 parts by mass of the lithium transition metal oxide, respectively.

[0124] [Table 3]

[0125] As shown in Table 3, in Comparative Example 2-1, in which only iodine was added, and Comparative Example 3-1, in which only 0.3 parts by mass of boric acid was added, no improvement was observed compared to Comparative Example 1-1, in which neither iodine nor boric acid was added. In Comparative Example 4, in which only 0.5 parts by mass of boric acid was added, a slight improvement was observed compared to Comparative Example 1-1. On the other hand, in Examples 1-1 and 2, in which iodine and boric acid were added, the initial discharge capacity and initial efficiency were significantly improved compared to Comparative Example 4.

[0126] As shown in Table 3, the initial DC resistance increased significantly in Comparative Examples 3-1 and 4, in which boric acid was added, whereas the increase in initial DC resistance was suppressed in Examples 1-1 and 2, in which iodine and boric acid were added, compared to Comparative Examples 3-1 and 4. In particular, the increase in initial DC resistance was suppressed in Example 1-1, even compared to Comparative Example 2-1, in which only iodine was added, and in Example 2, the increase in DC resistance was suppressed to the same extent as in Comparative Example 2-1.

[0127] (Results when carbon nanotubes are added) Table 4 shows the evaluation results of Evaluation Example 3-1 and Evaluation Example 3-2 for Example 1-2, Comparative Example 1-2, Comparative Example 2-2, and Comparative Example 3-2. Table 4 shows the evaluation results, including the initial charge capacity, initial discharge capacity, and initial efficiency at 25°C, the initial discharge capacity at 45°C, and the initial DC resistance and DC resistance ratio. However, for comparison, Table 4 lists relative values ​​obtained by dividing the actual values ​​by the corresponding values ​​in Comparative Example 1-2. The "Iodine" and "Boric Acid" columns list the values ​​of the parts by mass of iodine and boric acid added per 100 parts by mass of the lithium transition metal oxide, respectively.

[0128] [Table 4]

[0129] As shown in Table 4, the initial discharge capacity and initial efficiency of Comparative Example 2-2, in which only iodine was added, and Comparative Example 3-2, in which only boric acid was added, showed some improvement compared to Comparative Example 1-1, in which neither iodine nor boric acid was added. On the other hand, the initial discharge capacity and initial efficiency of Example 1-2, in which iodine and boric acid were added, were significantly improved compared to Comparative Examples 2-2 and 3-2.

[0130] As shown in Table 4, the initial DC resistance significantly increased in Comparative Example 3-2, in which boric acid was added, whereas the increase in initial DC resistance was suppressed in Example 1-2, in which iodine and boric acid were added, compared to Comparative Example 3-2. Moreover, the increase in initial DC resistance in Example 1-2 was suppressed even compared to Comparative Example 2-1, in which only iodine was added.

[0131] The results of Evaluation Examples 3-1 and 3-2 showed that the addition of boric acid tended to increase the initial capacity, initial efficiency, and initial DC resistance, while the addition of iodine tended not to increase the initial DC resistance as much as boric acid. On the other hand, the addition of both iodine and boric acid increased the initial capacity and initial efficiency while suppressing the increase in initial DC resistance. The fact that the initial DC resistance when iodine and boric acid were added was smaller than the initial DC resistance when iodine alone was suggested to suggest that the addition of iodine was not simply suppressing the increase in DC resistance due to boric acid. In other words, the addition of both iodine and boric acid resulted in a positive electrode active material that exhibited superior characteristics in both capacity and resistance compared to the use of either iodine or boric acid alone.

[0132] [Evaluation Example 4-1: Capacity Retention Rate] The mono-cell batteries manufactured in each example and comparative example were subjected to aging at 25°C at a current rate of 0.1 C for charging and 0.1 C for discharging. Next, in a thermostatic chamber maintained at 45°C, a charge / discharge cycle was repeated at a current rate of 0.3 C for charging and 0.3 C for discharging, with an upper limit charge voltage of 4.2 V and a lower limit discharge voltage of 2.5 V. From the discharge capacity in each cycle of the charge / discharge cycle, the capacity retention rate after the nth repeated charge / discharge cycle was calculated, as defined by the following formula:

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[0133] [Evaluation Example 4-2: Linear Resistance Increase Rate] The DC resistance of the mono-cell battery was measured for each cycle of the charge / discharge process in the same manner as in Evaluation Example 3-2. The linear resistance increase rate during the n-th repeated charge / discharge process was calculated from the measured DC resistance value. The linear resistance increase rate for Examples 1-1 and 2, and Comparative Examples 1-1, 2-1, 3-1, and 4 is defined by the following formula: To facilitate comparison of the changes in linear resistance between each Example and Comparative Example, the linear resistance increase rate at the 299th cycle in Comparative Example 1-1 was used as the reference value for normalization.

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[0134] The linear resistance increase rate for Example 1-2 and Comparative Examples 1-2, 2-2, and 3-2 is defined by the following formula: To make it easier to compare the changes in linear resistance between each Example and each Comparative Example, the linear resistance increase rate at the 299th cycle in Comparative Example 1-2 was used as the reference value for normalization.

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[0135] (Results without adding carbon nanotubes) FIG. 3 plots the values ​​of the capacity retention ratios defined above against the number of charge-discharge cycles for Examples 1-1 and 2, and Comparative Examples 1-1, 2-1, 3-1, and 4, showing the transition of battery capacity change during the 1st to 50th charge-discharge processes. For each Example and Comparative Example, the discharge capacity at the 1st cycle was taken as 100%. The battery capacity degradation was relatively large in Comparative Examples 3-1 and 4, but relatively small in Examples 1-1, 2, and 2-1. In Comparative Examples 1-1 and 3-1, fluctuations in the capacity retention ratios with respect to the number of cycles were observed. In FIG. 3, the 1st to 50th cycles are enlarged to clearly show the fluctuations.

[0136] FIG. 4 is a graph showing the change in linear resistance of the battery over the 1st to 200th charge-discharge cycles, plotting the linear resistance increase rate defined above against the number of charge-discharge cycles for Examples 1-1 and 2, and Comparative Examples 1-1, 2-1, 3-1, and 4. In all Examples and Comparative Examples, the linear resistance increased as the charge-discharge cycle was repeated. Comparing the linear resistance increase rates, Example 1-1 exhibited the smallest linear resistance increase rate, and Example 2 exhibited the next smallest linear resistance increase rate. On the other hand, Comparative Example 1-1 exhibited the largest linear resistance increase rate.

[0137] (Results when carbon nanotubes are added) FIG. 5 plots the values ​​of the capacity retention ratios defined above against the number of charge-discharge cycles for Example 1-2 and Comparative Examples 1-2, 2-2, and 3-2, showing the progress of battery capacity change over the course of the 1st to 50th charge-discharge cycles. For each Example and Comparative Example, the discharge capacity at the first cycle was taken as 100%. The battery capacity degradation was relatively large in Comparative Examples 1-2 and 3-2, but relatively small in Example 1-2 and 2-2. In Comparative Examples 1-2 and 3-2, the capacity retention ratios fluctuated significantly with the number of cycles, indicating a large fluctuation.

[0138] Figure 6 shows the change in linear resistance of the battery over the 1st to 200th charge-discharge cycles, plotting the linear resistance increase rate defined above against the number of charge-discharge cycles for Example 1-2, Comparative Example 1-2, Comparative Example 2-2, and Comparative Example 3-2. As in Figure 4, the linear resistance increased as the charge-discharge cycle was repeated in all Examples and Comparative Examples. Comparing the linear resistance increase rates, Example 1-2 showed the smallest linear resistance increase rate, and Comparative Example 1-2 showed the largest linear resistance increase rate.

[0139] [Evaluation Example 5: Impedance after repeated charge / discharge] For the mono-cell batteries manufactured in Examples 1-1 and 1-2, and Comparative Examples 1-1, 1-2, 2-1, 2-2, 3-1, and 3-2, the impedance of each battery was measured using an impedance analyzer after the first and 299th cycles of charging in the charge-discharge cycle test in Evaluation Example 4. The negative electrode impedance was calculated from the negative electrode impedance component appearing on the high frequency side (1,000,000 Hz to 100 Hz) in the resulting Cole-Cole plot. The positive electrode impedance was calculated from the positive electrode impedance component appearing on the low frequency side (100 Hz to 0.01 Hz). The results are shown in Table 5. In Table 5, the impedance is expressed as a relative value (relative impedance) to the impedance value at the first or 299th cycle of Comparative Example 1-1, as shown in the following equation: In the "Iodine, Boron" column, examples where only iodine was added are marked "I", examples where only boron was added are marked "B", examples where iodine and boron were added are marked "I, B", and examples where neither iodine nor boron was added are marked "-".

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[0140] [Table 5]

[0141] First, we will examine Example 1-1, Comparative Example 1-1, Comparative Example 2-1, and Comparative Example 3-1, which do not use carbon nanotubes as the conductive material. Comparing Comparative Example 1-1, which does not contain iodine or boron, with Comparative Example 2-1, which contains only iodine, we found that the initial impedance after the first charge did not change significantly with the addition of iodine, but the impedance on the low-frequency side significantly decreased after repeated charge-discharge cycles. On the other hand, comparing Comparative Example 1-1, which does not contain iodine or boron, with Comparative Example 3-1, which contains only boron, we found that the initial impedance after the first charge increased significantly on the low-frequency side with the addition of boron, but after repeated charge-discharge cycles, the impedance on both the high- and low-frequency sides significantly decreased, and the impedance on the low-frequency side also decreased to a value similar to that of Comparative Example 1-1. This suggests that adding iodine has the effect of lowering the impedance on the low-frequency side (positive electrode side), and adding boron has the effect of lowering the impedance on the high-frequency side (negative electrode side). In Example 1-1, in which iodine and boron were added, it was possible to achieve both the effect of reducing the impedance on the low frequency side (positive electrode side) and the effect of reducing the impedance on the high frequency side (negative electrode side). Furthermore, in Example 1-1, it was possible to suppress a large increase in the initial impedance on the low frequency side due to the addition of boron.

[0142] Next, when Example 1-2, Comparative Example 1-2, Comparative Example 2-2, and Comparative Example 3-2, which used carbon nanotubes as the conductive material, were compared, the same tendency as when carbon nanotubes were not used was confirmed overall. Furthermore, when Example 1-1 and Example 1-2, which differ in the presence or absence of carbon nanotubes, were compared, it was confirmed that the use of carbon nanotubes reduced the impedance on both the high-frequency side and the low-frequency side both before and after the charge-discharge cycle.

[0143] [Reference example 1] Fig. 7 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 / 57 shows the XPS spectrum of Example 1-1. It was confirmed from Figure 7 that when H5IO6 was 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, was obtained. Note that orthoperiodic acid (H5IO6) melts at 132°C, and then dehydration begins to produce 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 core comprising a lithium transition metal oxide; a coating portion that at least partially covers a surface of the core, the coating portion including iodine and boron; Including, The coating portion is a positive electrode active material containing iodine having an oxidation number of +5 or more and +7 or less.

2. A core comprising a lithium transition metal oxide; a coating portion that at least partially covers a surface of the core, the coating portion including iodine and boron; A positive electrode active material comprising: I3d observed by X-ray photoelectron spectroscopy of the positive electrode active material ５／２ The spectrum has a peak between 622 eV and 626 eV. Cathode active material.

3. The content of the iodine is 0.001 parts by mass to 5 parts by mass relative to 100 parts by mass of the lithium transition metal oxide. The positive electrode active material according to claim 1 .

4. The content of the boron is 0.001 parts by mass to 5 parts by mass relative to 100 parts by mass of the lithium transition metal oxide. The positive electrode active material according to claim 1 .

5. 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 4.

6. 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 4 formed on a current collector.

7. The positive electrode active material layer further contains a conductive agent containing carbon nanotubes. The positive electrode according to claim 6 .

8. A lithium ion secondary battery comprising the positive electrode according to claim 6 or 7.

9. A method for producing a positive electrode active material having a coating portion, comprising: obtaining a mixture comprising a lithium transition metal oxide, iodine, and boron; calcining the mixture; and Including, the coating portion contains iodine having an oxidation number of +5 or more and +7 or less.

10. adding an iodine material containing iodine as a raw material of the mixture; The iodine 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 9 .

11. The iodine material is elemental iodine (I ２ ), including The method for producing a positive electrode active material according to claim 10 .

12. Adding a boron material containing boron as a raw material of the mixture; The boron material is H ３ BO ３ , HBO ２ , B ２ O ３ , LiBO ２ , C ６ H ５ B(OH) ２ , (C ６ H ５ O) ３ B, [CH ３ (CH ２ ) ３ O] ３ B, C １３ H １９ BO ３ , C ３ H ９ B ３ O ６ , and (C ３ H ７ O) ３ B. The method for producing a positive electrode active material according to any one of claims 9 to 11.

13. The boron material is boric acid (H ３ BO ３ ), including The method for producing a positive electrode active material according to claim 12.

14. and firing the mixture at a firing temperature of 150°C or higher and 500°C or lower. The method for producing a positive electrode active material according to any one of claims 9 to 13.

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