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

Abstract

Provided are a positive electrode active material for a lithium ion secondary battery having 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. The positive electrode active material includes a core including a lithium transition metal oxide, and a coated portion at least partially covering a surface of the core and including iodine and boron.

Description

Technical Field

[0001] This disclosure relates to positive electrode active materials, positive electrode active material slurries, positive electrodes, lithium-ion secondary batteries, and methods for preparing positive electrode active materials.

[0002] This application claims priority to Japanese Patent Application No. 2021-212767, filed on December 27, 2021, the disclosure of which is incorporated herein by reference. Background Technology

[0003] With the development of mobile device technology, the demand for secondary batteries as an energy source is increasing. Among these secondary batteries, lithium-ion batteries, characterized by high energy density, high operating voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. Currently, active research is underway to develop high-capacity lithium-ion secondary batteries.

[0004] For example, known techniques for providing high-capacity lithium-ion secondary batteries include forming a boron-based coating on the surface of the electrode active material.

[0005] [References]

[0006] [Patent Literature]

[0007] Patent Document 1: Japanese Patent No. 6284542

[0008] Patent Document 2: Japanese Patent Application Publication No. 2017-152275

[0009] Patent Document 3: Japanese Patent Application Publication No. 2019-175872 Summary of the Invention

[0010] Technical issues

[0011] However, when forming such coatings, there are cases where the electrode resistance characteristics cannot be fully obtained. Therefore, it is necessary to balance excellent capacitance characteristics and electrode resistance characteristics.

[0012] Therefore, this disclosure aims to provide positive electrode active materials for lithium-ion secondary batteries, positive electrode active material slurries, positive electrodes, lithium-ion secondary batteries, and methods for preparing positive electrode active materials, all having excellent capacity and electrode resistance characteristics.

[0013] Technical solution

[0014] According to one embodiment of the present disclosure, a positive electrode active material is provided, comprising a core containing a lithium transition metal oxide, and a coating portion that at least partially covers the surface of the core and comprises iodine and boron.

[0015] As used herein, "lithium transition metal oxide" refers to a compound containing lithium and a transition metal and having a transition metal-oxygen bond, and also includes compounds that further contain common metallic elements (e.g., aluminum) or non-metallic elements (e.g., iodine) in addition to oxygen. In this document, the term "coating" means at least partially covering the surface of an object, and also includes cases where chemical bonds exist on the particle surface and cases where the particle surface is physically covered in the absence of chemical bonds. For example, when peaks from iodine and boron are detected in X-ray photoelectron spectroscopy (XPS) of the surface of active material particles, it can be referred to as "forming a coating portion containing iodine and boron".

[0016] In the positive electrode active material defined in the above embodiments, the coating portion may include iodine with an oxidation state of +5 to +7.

[0017] In the positive electrode active material defined in the above embodiments, I3d is observed by X-ray photoelectron spectroscopy of the positive electrode active material. 5 / 2 The spectrum can have peaks in the range of 622 eV to 626 eV.

[0018] In the positive electrode active material defined in the above embodiments, the iodine content can be from 0.001 parts by weight to 5 parts by weight based on 100 parts by weight of lithium transition metal oxide.

[0019] In the positive electrode active material defined in the above embodiments, the boron content can be from 0.001 parts by weight to 5 parts by weight based on 100 parts by weight of lithium transition metal oxide.

[0020] According to another embodiment of this disclosure, a positive electrode active material slurry for lithium-ion secondary batteries is provided, which includes the positive electrode active material defined in the above embodiments.

[0021] According to another embodiment of this disclosure, a positive electrode for a lithium-ion secondary battery is provided, which has a positive electrode active material layer, the positive electrode active material layer comprising the positive electrode active material defined in the above embodiments and formed on a current collector.

[0022] In the positive electrode defined in the above embodiments, the positive electrode active material layer may further include a conductive material containing carbon nanotubes.

[0023] According to another aspect of the present invention, a lithium-ion secondary battery is provided, which includes a positive electrode as defined in the above embodiments.

[0024] According to another embodiment of this disclosure, a method for preparing a positive electrode active material is provided, comprising the steps of: preparing a mixture containing lithium transition metal oxide, iodine and boron; and calcining the mixture.

[0025] The method for preparing the positive electrode active material as defined in the above embodiments may include the step of adding an iodine-containing component as a component of the mixture. The iodine component may include at least one 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 iodate (LiIO₃), sodium iodate (NaIO₃), potassium iodate (KIO₃), ammonium iodate (NH₄IO₃), metaperiodic acid (HIO₄), orthoperiodic acid (H₅IO₆), lithium periodate (LiIO₄), sodium periodate (NaIO₄), potassium periodate (KIO₄), iodine oxide (IV) (I₂O₄), iodine oxide (V) (I₂O₅), and iodine oxide (IV,V) (I₄O₉). As used herein, "iodine component" means any component containing iodine.

[0026] In the method for preparing the positive electrode active material defined in the above embodiments, the iodine component may include elemental iodine (I2).

[0027] The method for preparing the positive electrode active material as defined in the above embodiments may include adding a boron-containing component as a component of the mixture. The boron component may include at least one selected from the group consisting of: H3BO3, HBO2, B2O3, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, C 13 H 19 BO3, C3H9B3O6, and (C3H7O)3B. As used herein, "boron component" refers to any component containing boron.

[0028] In the method for preparing the positive electrode active material defined in the above embodiments, the boron component may include boric acid (H3BO3).

[0029] The method for preparing the positive electrode active material as defined in the above embodiments may include the step of firing the mixture at a firing temperature of 150°C to 500°C.

[0030] Beneficial effects

[0031] According to this disclosure, a positive electrode active material for lithium-ion secondary batteries, a positive electrode active material slurry, a positive electrode, a lithium-ion secondary battery, and a method for preparing the positive electrode active material can be provided, all having excellent capacity and electrode resistance characteristics. Attached Figure Description

[0032] Figure 1 Partial spectra of the positive electrode active materials of Examples 1-1 and Comparative Examples 1-1, 2-1 and 3-1 as analyzed by X-ray photoelectron spectroscopy (XPS) are shown.

[0033] Figure 2 Partial spectra of the positive electrode active materials of Examples 1-1 and Comparative Examples 1-1, 2-1 and 3-1 as analyzed by XPS are shown.

[0034] Figure 3 The changes in battery capacity during the 1st to 50th charge-discharge cycles are shown in Examples 1-1 and 2 and Comparative Examples 1-1, 2-1, 3-1 and 4.

[0035] Figure 4 The changes in DC resistance during the 1st to 200th charge-discharge cycles are shown in Examples 1-1 and 2, and Comparative Examples 1-1, 2-1, 3-1 and 4.

[0036] Figure 5 The changes in battery capacity during the 1st to 50th charge-discharge cycles are shown in Examples 1-2 and Comparative Examples 1-2, 2-2, and 3-2.

[0037] Figure 6 The changes in DC resistance during the 1st to 200th charge-discharge cycles in Examples 1-2 and Comparative Examples 1-2, 2-2, and 3-2 are shown.

[0038] Figure 7 A portion of the spectrum of the positive electrode active material of Reference Example 1, analyzed by XPS, is shown. Detailed Implementation

[0039] Preferred embodiments of the present disclosure will be described in detail below. However, the descriptions presented herein are merely preferred embodiments for illustrative purposes and are not intended to limit the scope of the disclosure.

[0040] Regarding the issue of electrode resistance characteristics that may arise when providing high capacity for lithium-ion secondary batteries, the following description will use a lithium-ion secondary battery that uses nickel-rich lithium transition metal oxides as the positive electrode active material as an example.

[0041] In lithium-ion secondary battery cathode materials, lithium-nickel-cobalt-manganese ternary cathode active materials (such as Li) are used as cathode materials. a Ni x Co y Mn zIn lithium-ion batteries (LiCoO2), it is known that increasing the nickel content in the composition can help provide high-capacity batteries. In fact, there has been a persistent market demand for high-capacity lithium-ion rechargeable batteries, and therefore, nickel-rich cathode active materials with high capacity per unit weight in the 3.0V to 4.2V operating voltage range have been actively developed as alternatives to conventionally used LiCoO2. However, in such lithium-nickel-cobalt-manganese ternary cathode materials, as the Ni content increases, problems such as gas generation at high temperatures or decreased stability under charging conditions arise, which become serious issues when applying this cathode material to batteries.

[0042] To address the aforementioned issues, methods have been proposed for forming coatings on the surface of cathode active material particles to suppress gas generation or achieve stable cycling behavior. However, in nickel-rich cathodes with high nickel content, such coating treatments significantly increase the resistive component, and in some cases, discharge capacity or rate performance may decrease, or cycling performance may deteriorate. In this context, while methods for forming boron-based coatings are known, as disclosed in Patent Documents 1 and 2, their applicability to nickel-rich cathodes is limited. Meanwhile, as disclosed in Patent Document 3, methods for forming boron-based coatings and another type of coating have been discussed. However, there is a practical problem that coating stacking can lead to increased electrode resistance. Therefore, in currently used or developing active materials, there are significant limitations in coating techniques that can balance excellent capacity characteristics and electrode resistance characteristics.

[0043] The inventors of this disclosure have discovered that when using a positive electrode active material containing a lithium transition metal oxide in a lithium-ion secondary battery, a lithium-ion secondary battery with excellent electrode resistance and capacity characteristics can be obtained by forming a coating containing iodine and boron on the surface of the core containing the lithium transition metal oxide. This disclosure is based on this discovery.

[0044] [Positive electrode active material]

[0045] In one aspect of this disclosure, a positive electrode active material is provided, comprising a core containing a lithium transition metal oxide, and a coating portion that at least partially covers the surface of the core and comprises iodine and boron. Preferably, the positive electrode active material is a positive electrode active material for lithium-ion secondary batteries.

[0046] The positive electrode active material may include lithium transition metal oxides, iodine, and boron capable of lithium intercalation / deintercalation. The positive electrode active material may be in the form of particles having a core-shell structure formed by a core and a coating portion. The coating portion may completely cover the core or partially cover the outer surface of the core. The coating portion may be interconnected as a whole or may have multiple island-like portions spaced apart from each other. The coating portion may cover a single core or two or more cores.

[0047] (nuclear)

[0048] The core of the positive electrode active material comprises a lithium transition metal oxide. For example, the core may be lithium transition metal oxide particles. Meanwhile, the core may contain components other than the lithium transition metal oxide. The shape of the core is not particularly limited and may have any optional shape, such as a spherical shape, a cubic shape or a polygonal shape. In addition, the particle shape is not particularly limited. For example, the core may be formed of a single particle, or may be formed of an aggregate, such as a secondary particle formed by aggregation of primary particles. Although the size of the core is not particularly limited, the size of the core may be 0.01 µm to 30 µm, 0.1 µm to 10 µm, or the like.

[0049] For example, the core of the positive electrode active material may include a nickel-containing lithium transition metal oxide, preferably a nickel-rich lithium transition metal oxide. As used herein, "nickel-rich" means that the nickel content is 50 mol% or more based on the total content of transition metals. As described above, a nickel-rich lithium transition metal oxide containing 50 mol% or more of nickel is preferable in terms of suppressing an increase in electrode resistance. Therefore, when the positive electrode active material according to the present embodiment is used, electrode resistance characteristics can be improved (that is, resistance increase can be reduced), thereby contributing to balancing the high capacity characteristics and improved electrode resistance characteristics of a lithium-ion secondary battery. For example, based on the total content of transition metals, the core may include a lithium transition metal oxide having a nickel content of 60 mol% or more, 70 mol% or more, 80 mol% or more, or 90 mol% or more.

[0050] (Lithium transition metal oxide)

[0051] Specific examples of the lithium transition metal oxide may include: lithium manganese-based oxides (e.g., LiMnO2, LiMnO3, LiMn2O3, LiMn2O4, etc.); lithium cobalt oxides (e.g., LiCoO2, etc.); lithium nickel oxides (e.g., LiNiO2, etc.); lithium copper oxides (e.g., Li2CuO2, etc.); lithium vanadium oxides (e.g., LiV3O8, etc.); lithium nickel manganese 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 oxides (e.g., LiNi 1-y Co y O2(0<y<1), etc.); lithium manganese cobalt 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 oxides (e.g., Li(Ni x Co y Mnz )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) oxides (e.g., Li(Ni x Co y Mn z M w )O2 (wherein 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.); lithium-excess solid solution positive electrodes (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 transition metal elements are partially substituted by one or more metal elements, etc. The positive electrode active material layer may comprise one or more compounds selected from the above compounds, but is not limited thereto.

[0052] Specific examples of nickel-rich lithium transition metal oxides that effectively provide high-capacity batteries may include: 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 yO₂(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(wherein 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(wherein 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); those compounds in which transition metal elements are partially substituted by one or more metal elements (e.g., one or more elements selected from Al, Fe, V, Cr, Ti, Ta, Mg, Mo, Zr, Zn, Ga and In); those compounds in which oxygen atoms are partially substituted by one or more non-metallic elements (e.g., one or more elements selected from P, F, S and N), etc. The positive electrode active material may comprise one or more compounds selected from the above compounds, but is not limited thereto. In addition, in the same particle, there may be a distribution of substitution degree from the inside to the surface layer. Furthermore, the particles may be surface-coated. For example, the surface may be coated with metal oxide, lithium transition metal oxide, polymer, etc., but is not limited thereto.

[0053] Specifically, in terms of improving the capacity characteristics and stability of the battery, a preferred lithium transition metal oxide may comprise 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 zO2(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 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. In this paper, the range of the value of "a" can satisfy the condition 0.5≤a≤1.5, preferably 1.0≤a≤1.5.

[0054] More specifically, LiNiO2 and Li(Ni) are preferred. 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 O2, 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.

[0055] (Coated area)

[0056] The coating portion of the positive electrode active material partially or completely covers the surface of the core. The coating portion comprises iodine and boron. The coating portion is obtained by mixing lithium transition metal oxide, iodine, and boron and then firing the resulting mixture. The coating portion of the positive electrode active material can exist independently of the lithium transition metal oxide-containing core, or it can be at least partially bonded to the surface of the lithium transition metal oxide particles forming the core in a chemical or physical manner. Preferably, the coating portion is at least partially in contact with the lithium transition metal oxide particles. The coating portion can be at least partially contained within the structure of the lithium transition metal oxide. Furthermore, the composition of the coating portion is not limited to chemical substances that are compounds independently, and can include any chemical substance, such as ions, atoms, or atomic groups. Although the thickness of the coating portion is not particularly limited, the conductivity of the core surface is limited when the coating portion completely covers the core surface or has a large thickness. Therefore, the thickness of the coating portion is preferably 0.1 nm to 10 nm, more preferably 3 nm to 5 nm. Additionally, the use of carbon nanotubes or similar materials to interconnect the particles is effective in suppressing conductivity degradation.

[0057] For example, the content of the coating portion in the positive electrode active material can be from 0.001 wt% to 10.0 wt%, preferably from 0.01 wt% to 1.0 wt%, more preferably from 0.02 wt% to 0.5 wt%, and even more preferably from 0.05 wt% to 0.2 wt%. When the content of the coating portion is 0.001 wt% or more, it is desirable to improve the cycle characteristics or electrode resistance characteristics of the battery.

[0058] (Iodine content)

[0059] After firing, the coating portion of the positive electrode active material contains iodine with a positive oxidation state. For example, the coating portion includes iodine with an oxidation state of +1 to +7, preferably iodine with an oxidation state of +2 to +7, more preferably iodine with an oxidation state of +5 to +7, and even more preferably iodine with an oxidation state of +7. Iodine with a positive oxidation state generally has strong oxidizing power. For example, iodine compounds with a positive oxidation state include: iodic acid, such as iodic acid (HIO3), metaperiodic acid (HIO4), or orthoperiodic acid (H5IO6); iodates, such as lithium iodate (LiIO3), sodium iodate (NaIO3), potassium iodate (KIO3), ammonium iodate (NH4IO3), lithium periodate (LiIO4), sodium periodate (NaIO4), or potassium periodate (KIO4); iodine oxides, such as iodine oxide (IV)(I2O4), iodine oxide (V)(I2O5), and iodine oxide (IV,V)(I4O9), etc. The coating may include periodate ions or hydrogen periodate ions. Periodate ions may include metaperiodate ions (IO4). - ), original periodate ion (IO6) 5- (e.g., periodate ions can include HIO6) 4- H2IO6 3- H3IO6 2 H4IO6 - Additionally, the iodine contained in the coating portion can combine with elements that form lithium transition metal oxides (lithium, transition metals, oxygen, etc.) or with boron. For example, the coating portion may include iodate ions (IO3-) that are combined with metal ions of lithium transition metal oxides. - Or periodate ions. For example, the coating may include a combination of metal cations such as lithium transition metal oxides and periodate ions, particularly metal cations and periodate ions (IO4). - The combination of ).

[0060] In the positive electrode active material, the iodine content can be from 0.001 parts by weight to 5 parts by weight based on 100 parts by weight of lithium transition metal oxide. When the iodine content is 0.001 parts by weight or more, it is desirable to improve the electrode resistance characteristics or cycle characteristics of the battery. When the iodine content is 5 parts by weight or less, it is believed that side reactions caused by over-coating are suppressed. Based on 100 parts by weight of lithium transition metal oxide, the iodine content is preferably 0.005 parts by weight to 2 parts by weight, more preferably 0.01 parts by weight to 1 part by weight, and even more preferably 0.05 parts by weight to 0.5 parts by weight.

[0061] (Boron content)

[0062] After firing, the coating portion of the positive electrode active material includes boron with an oxidation state of +3. For example, boron compounds included in the coating portion include boric acid, borates, polyboronic acid, polyborates, boron oxide, etc. The boron included in the coating portion can be combined with elements of lithium transition metal oxides (lithium, transition metals, oxygen, etc.) or with iodine. For example, the coating portion may include borate ions (hereinafter, typically BO3) combined with metal ions of lithium transition metal oxides. 3- HBO3 2- (Borate ions are collectively referred to as "borate ions" along with H₂BO₃). For example, the coating portion may include a combination of metal cations such as lithium transition metal oxides and borate ions. For example, the coating portion may include lithium metaborate (LiBO₂). Furthermore, Patent Document 1 indicates that boric acid reacts with the remaining lithium to form lithium borate.

[0063] In the positive electrode active material, the boron content can be from 0.001 parts by weight to 5 parts by weight based on 100 parts by weight of lithium transition metal oxide. When the amount of boron added is 0.001 parts by weight or more, it is desirable to improve the capacity characteristics or cycle characteristics of the battery. When the boron content is 5 parts by weight or less, it is considered to suppress side reactions caused by over-coating. Based on 100 parts by weight of lithium transition metal oxide, the boron content is preferably 0.01 parts by weight to 3 parts by weight, more preferably 0.05 parts by weight to 2 parts by weight, and even more preferably 0.1 parts by weight to 1 part by weight.

[0064] XPS spectra of positive electrode active materials

[0065] The spectrum of the positive electrode active material observed by X-ray photoelectron spectroscopy (XPS) exhibits I3d ions derived from iodine. 5 / 2 The peak of electrons. When passing through -(CH2) n When performing charge correction on the peak energy of C1s at 284.6 eV, I3d 5 / 2The spectrum has a peak at 622 eV to 626 eV. The peak position is preferably 623 eV to 625 eV, more preferably 623.5 eV to 624.5 eV. Herein, "peak position" refers to the position (energy) of the peak maximum. This peak originates from iodine with a positive oxidation state. For example, the peak originates from iodine with an oxidation state of +1 to +7, preferably from iodine with an oxidation state of +3 to +7, more preferably from iodine with an oxidation state of +5 to +7, and even more preferably from iodine with an oxidation state of +7.

[0066] The spectrum of the positive electrode active material, observed by X-ray photoelectron spectroscopy (XPS), exhibits peaks originating from B1s electrons of boron. For example, when observed via electrons originating from -(CH2)... n When the peak energy of C1s electrons is 284.6 eV, the spectrum of boron's B1s electrons has peaks from 188.5 eV to 195.0 eV after charge correction.

[0067] It is believed that the coating improves the battery's capacity and electrode resistance characteristics and suppresses the degradation of cycle characteristics through the following mechanisms. However, the following mechanisms are merely exemplary assumptions to aid in understanding this disclosure, and the scope of this disclosure is not limited thereto.

[0068] It is believed that once lithium transition metal oxide, iodine, and boron are mixed and calcined, the iodine and boron components will induce chemical reactions on the lithium transition metal oxide, either individually or in combination, forming a coating containing iodine and boron; however, the details are unclear. While the specific function of the coating in the positive electrode active material is unknown, the aforementioned coating likely contains iodine, which has a positive oxidation number and strong electron attraction. Based on knowledge in the relevant field, it is known that by mixing a solid electrolyte with LiI, electrons are attracted to the highly electronegative I, thereby improving the ionic conductivity of Li. Therefore, it is believed that during charging, Li improves conductivity through the coating, thus accelerating the redox reaction of the positive electrode active material. Consequently, it is believed that side reactions occurring during charging (such as electrolyte decomposition) are suppressed, thereby inhibiting the increase in electrode resistance of the positive electrode and achieving stable long-term cycling characteristics.

[0069] Furthermore, it is believed that the coating at least partially covers the surface containing the lithium transition metal oxide core. Since the coating inhibits the chemical reaction between the lithium transition metal oxide and the electrolyte, thereby inhibiting the formation of by-reaction products, it is believed that adverse reactions can be suppressed, such as the formation of by-reaction products on the positive electrode active material during repeated charge / discharge, thereby suppressing cell reaction or increased battery resistance.

[0070] As described in the following examples, it was shown that the electrode resistance tends to increase when a boron-derived coating is formed. However, it was also shown that incorporating iodine into the coating portion suppressed the increase in electrode resistance. The increase in electrode resistance caused by the coating portion can be suppressed by the action of iodine, while improving and stabilizing battery performance through the coating portion. Meanwhile, it is unclear whether boron-containing coatings and iodine-containing coatings can be formed independently and function independently, or whether there is an interaction between boron and iodine.

[0071] In particular, nickel-rich lithium transition metal oxides are significantly affected by increased electrode resistance. Typically, metal oxide coatings for insulators (e.g., Al₂O₃) are effective in the case of lithium cobalt oxides, etc. However, in the case of Ni-containing layered compounds, these metal oxides lead to increased surface and electrode resistance, often resulting in insufficient battery performance. Meanwhile, boron coatings are known to have less impact on surface resistance compared to metal oxides, and are even effective for Ni-containing layered oxide materials. However, in the case of nickel-rich lithium transition metal oxides, they are even affected by a slight increase in resistance caused by boron, sometimes resulting in insufficient battery performance. In this case, when a coating containing boron and iodine is formed as described above, a balance between capacity and electrode resistance characteristics can be achieved even when using nickel-rich lithium transition metal oxides, which are easily affected by electrode resistance. Generally, batteries using nickel-rich lithium transition metal oxides tend to have larger capacities, thus offering advantages in providing high-capacity batteries.

[0072] [Preparation method of positive electrode active material]

[0073] According to another aspect of this disclosure, a method for preparing a positive electrode active material is provided, comprising the steps of: preparing a mixture containing lithium transition metal oxide, iodine and boron; and calcining the resulting mixture.

[0074] (1) Mixing

[0075] In the mixing process, at least one lithium transition metal oxide, iodine component, and boron component are mixed. For example, during the mixing process, all lithium transition metal oxide, iodine component, and boron component are mixed in a solid state. For example, powdered lithium transition metal oxide, iodine component, and boron component can be mixed to obtain a powdered mixture. Hereinafter, the resulting mixture is referred to as the "pre-firing mixture." There are no particular limitations on the mixing process, and any known method can be used. The mixing step can be carried out in air or under other atmospheres, such as an inert atmosphere. Additionally, any component other than lithium transition metal oxide, iodine component, and boron component can be added. Because the components are mixed in a solid state, the mixing process can be carried out in a simple manner, thus being cost-effective and suitable for large-scale production.

[0076] (Iodine content)

[0077] Iodine is used to introduce iodine into the positive electrode active material. The iodine is preferably solid at room temperature to facilitate mixing with lithium transition metal oxides. For example, the iodine may include at least one 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 iodate (LiIO₃), sodium iodate (NaIO₃), potassium iodate (KIO₃), ammonium iodate (NH₄IO₃), metaperiodic acid (HIO₄), orthoperiodic acid (H₅IO₆), lithium periodate (LiIO₄), sodium periodate (NaIO₄), potassium periodate (KIO₄), iodine oxide (IV) (I₂O₄), iodine oxide (V) (I₂O₅), and iodine oxide (IV,V) (I₄O₉). Any iodine other than those listed above, such as metal iodides or iodine-containing organic compounds, may be used, provided it does not adversely affect the battery characteristics. At the same time, there are no special restrictions on the valence of iodine in the iodine component.

[0078] (Boron content)

[0079] Boron is a component used to introduce boron into the positive electrode active material. The boron component is preferably in a solid state at room temperature to facilitate mixing with lithium transition metal oxides. For example, the boron component may include those selected from H3BO3, HBO2, B2O3, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, C... 13 H 19 At least one of the following groups: BO3, C3H9B3O6, and (C3H7O)3B. Any boron component other than those listed above, such as metal borides, may be used, provided it does not adversely affect the characteristics of the battery. Furthermore, there are no particular restrictions on the valence of boron in the boron component.

[0080] For example, based on the total weight of 100 parts by weight of the mixture before firing, the amount of lithium transition metal oxide added during the mixing process is 85 to 99.98 parts by weight, preferably 90 to 99.9 parts by weight, and more preferably 95 to 99.5 parts by weight.

[0081] For example, based on the total weight of 100 parts by weight of the mixture before firing, the amount of iodine added during the mixing process is 0.001 parts by weight to 5 parts by weight, preferably 0.01 parts by weight to 4 parts by weight, more preferably 0.05 parts by weight to 3 parts by weight, and even more preferably 0.1 parts by weight to 2 parts by weight. When the amount of iodine added is 0.001 parts by weight or more, it is desirable to improve the electrode resistance characteristics or cycle characteristics of the battery. When the amount of iodine added is 5 parts by weight or less, it is considered that excessive side reactions are suppressed.

[0082] For example, based on the total weight of 100 parts by weight of the mixture before firing, the amount of boron added during the mixing process is 0.01 parts by weight to 5 parts by weight, preferably 0.05 parts by weight to 4 parts by weight, more preferably 0.1 parts by weight to 3 parts by weight, and even more preferably 0.5 parts by weight to 2 parts by weight. When the amount of boron added is 0.01 parts by weight or more, it is desirable to improve the electrode resistance characteristics or cycle characteristics of the battery. When the amount of boron added is 5 parts by weight or less, it is considered that excessive side reactions are suppressed.

[0083] (2) Firing

[0084] In the firing process, the mixture obtained in the mixing step before firing is fired to obtain a positive electrode active material. The firing process is preferably carried out in the presence of oxygen, more preferably in an ambient atmosphere, but can also be carried out in any atmosphere other than those mentioned above. For example, the firing process can be carried out in an inert atmosphere, such as a nitrogen atmosphere or a rare gas atmosphere including argon. When firing is carried out in an ambient atmosphere, the firing steps can be performed in a simple manner, thus being cost-effective and suitable for large-scale production.

[0085] For example, the firing temperature of the mixture can be from 150°C to 500°C, preferably from 200°C to 450°C, more preferably from 250°C to 400°C, and even more preferably from 300°C to 350°C. When the firing temperature is above 150°C, it is believed that the reaction between the iodine and boron components may be accelerated. Furthermore, when the firing temperature is below 500°C, excessive formation of by-products can be suppressed. Additionally, the firing temperature of the mixture is preferably greater than or equal to the melting points of the iodine and boron components, and more preferably greater than or equal to the boiling points of the iodine and boron components.

[0086] For example, the firing time for maintaining the mixture at the firing temperature can be from 1 hour to 12 hours, preferably from 1 hour to 9 hours, more preferably from 1.5 hours to 6 hours, and even more preferably from 2 hours to 5 hours. When the firing time is more than 1 hour, it is believed that the iodine and boron components can react within the desired range. In addition, when the firing time is less than 12 hours, excessively long firing times are avoided, thus suppressing the increase in costs.

[0087] [Positive Electrode Active Material Slurry]

[0088] In another aspect of this disclosure, a positive electrode active material slurry for lithium secondary batteries is provided, comprising the aforementioned positive electrode active material. For example, the positive electrode active material slurry includes a positive electrode active material, a conductive material, a binder, and a solvent.

[0089] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material contained in the positive electrode active material layer can be from 80% to 99.5% by weight. Preferably, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be from 85% to 98.5% by weight. When the content of the positive electrode active material falls within the above-defined range, excellent capacity characteristics can be achieved. However, when the content of the positive electrode active material is below the above-defined range, the coating amount on the positive electrode increases, resulting in increased thickness, and therefore it is likely that sufficient volumetric energy density cannot be achieved. When the content of the positive electrode active material exceeds the above-defined range, the binder and conductive material are insufficient, leading to deterioration of the conductivity and adhesion of the electrode and deterioration of battery performance.

[0090] (Conductive materials)

[0091] There are no particular limitations on conductive materials, as long as they are conductive materials that do not cause chemical changes in the corresponding battery. Specific examples of conductive materials include, but are not limited to: carbonaceous materials, such as artificial graphite, natural graphite, carbon black, acetylene black, Ketjen black, Denka black, thermally cracked carbon black, channel black, furnace black, lamp black, or thermally cracked carbon black, carbon nanotubes, carbon fibers, etc.; metal powders or 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, iridium, etc.; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; conductive polymers, such as polyaniline, polythiophene, polyacetylene, polypyrrole, polyphenylene derivatives, etc. Such conductive compounds can be used alone or in combination.

[0092] As described in the following examples, when carbon nanotubes are used as a conductive material, the impedance of the electrode can be significantly reduced. Therefore, the positive electrode active material slurry preferably includes carbon nanotubes.

[0093] Based on the total weight of the positive electrode active material layer, the content of conductive material can be from 0.1% to 30% by weight. Based on the total weight of the positive electrode active material layer, the content of conductive material is preferably from 0.5% to 15% by weight, more preferably from 0.5% to 5% by weight. When the content of conductive material meets the above-defined range, sufficient conductivity can be imparted and battery capacity can be ensured since the content of positive electrode active material is not reduced.

[0094] (Adhesive)

[0095] Adhesives are components that facilitate the bonding between active and conductive materials, as well as with current collectors. Specific examples of adhesives include, but are not limited to, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. Such adhesives can be used alone or in combination.

[0096] Preferably, the binder content can be from 0.1% to 30% by weight, based on the total weight of the positive electrode active material layer. The binder content is preferably from 0.5% to 15% by weight, more preferably from 0.5% to 5% by weight, based on the total weight of the positive electrode active material layer. When the binder polymer content meets the above-defined range, sufficient adhesion can be imparted to the electrode while preventing deterioration of battery capacity characteristics.

[0097] (solvent)

[0098] There are no particular restrictions on the solvents used in the positive electrode active material slurry, as long as they are conventional solvents used in the manufacture of the positive electrode. Specific examples of solvents include, but are not limited to: amine solvents, such as N,N-dimethylaminopropylamine, diethylenetriamine, N,N-dimethylformamide (DMF), etc.; ether solvents, such as tetrahydrofuran; ketone solvents, such as methyl ethyl ketone; ester solvents, such as methyl acetate; amide solvents, such as dimethylacetamide, 1-methyl-2-pyrrolidone (NMP), etc.; dimethyl sulfoxide (DMSO); water, etc. Such solvents can be used alone or in combination.

[0099] Considering the coating thickness or yield of the slurry, the amount of solvent used can provide a viscosity that allows the slurry to exhibit excellent thickness uniformity when coated onto the positive electrode current collector, while dissolving or dispersing the positive electrode active material, conductive material, and binder.

[0100] [Method for preparing positive electrode active material slurry]

[0101] A positive electrode active material slurry is obtained by adding conductive materials, binders, solvents, etc., to the above-mentioned positive electrode active material and then mixing them. Other additives, such as dispersants and thickeners, can be added if necessary.

[0102] [positive electrode]

[0103] In another aspect of this disclosure, a positive electrode for a lithium-ion secondary battery is provided, comprising a positive electrode active material layer containing the aforementioned positive electrode active material and formed on a current collector. That is, the positive electrode comprises 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 wholly or partially on the surface of the positive electrode current collector. For example, the positive electrode is for a lithium-ion secondary battery containing an electrolyte.

[0104] (Positive current collector)

[0105] There are no particular restrictions on the positive electrode current collector used, as long as it is electrochemically stable and conductive. Specific examples of positive electrode current collectors include: stainless steel; aluminum; nickel; titanium; or alloys, combinations, or mixtures thereof. Alternatively, calcined aluminum or stainless steel or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, or silver can also be used.

[0106] The thickness of the positive electrode current collector can range from 3 μm to 500 μm. Fine surface irregularities can be formed on the surface of the positive electrode current collector to enhance adhesion to the positive electrode active material. For example, the positive electrode current collector can have various shapes, such as membranes, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0107] (Positive electrode active material layer)

[0108] The positive electrode active material layer includes the aforementioned positive electrode active material, conductive material, and binder. For example, the thickness of the positive electrode active material layer can be 1 nm to 100 μm, 10 nm to 10 μm, or 100 nm to 1 μm. The positive electrode active material layer can be formed directly on the positive electrode current collector, or it can be formed with another layer inserted between the positive electrode active material layer and the positive electrode current collector. Additionally, an additional layer, such as a protective film, can be formed on the positive electrode active material layer.

[0109] The positive electrode active material layer can include a conductive material containing carbon nanotubes. In this case, the electrode impedance can be significantly reduced, thus improving the electrode resistance characteristics.

[0110] [Manufacturing method of the positive electrode]

[0111] By coating a slurry of positive electrode active material onto a positive electrode current collector and then drying and pressing it, a positive electrode containing a layer of positive electrode active material formed on the positive electrode current collector can be obtained.

[0112] In one variation, a positive electrode active material slurry can be cast onto another support, then the slurry can be peeled off from the support to obtain a membrane, which is then laminated onto a positive electrode current collector to obtain a positive electrode. Alternatively, other alternative methods can be used to form a positive electrode active material layer on the positive electrode current collector.

[0113] [Lithium-ion rechargeable battery]

[0114] According to another aspect of the present invention, a lithium secondary battery comprising the positive electrode is provided. For example, the lithium-ion secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte. Meanwhile, when a solid electrolyte is used as the non-aqueous electrolyte, the separator can be omitted. The lithium-ion secondary battery may optionally include a battery casing configured to house an electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member configured to seal the battery casing.

[0115] [negative electrode]

[0116] In the lithium-ion secondary battery defined in the above embodiments, 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 wholly or partially on the surface of the negative electrode current collector.

[0117] (Negative electrode current collector)

[0118] There are no particular restrictions on the negative electrode current collector used, as long as it is electrochemically stable and conductive. Specific examples of negative electrode current collectors include: copper; stainless steel; aluminum; nickel; titanium; sintered carbon; or copper or stainless steel with surface treatments such as carbon, nickel, titanium, or silver; or aluminum-cadmium alloys, etc.

[0119] The thickness of the negative electrode current collector can range from 3 μm to 500 μm. Fine surface irregularities can be formed on the surface of the negative electrode current collector to enhance adhesion to the negative electrode active material. For example, the negative electrode current collector can have various shapes, such as membranes, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0120] (Negative electrode active material slurry)

[0121] The negative electrode active material layer comprises a negative electrode active material, a conductive material, and a binder. For example, the thickness of the negative electrode active material layer can be 1 nm to 100 μm, 10 nm to 10 μm, or 100 nm to 1 μm. The negative electrode active material layer can be formed directly on the negative electrode current collector, or it can be formed with another layer inserted between the negative electrode active material layer and the negative electrode current collector. Additionally, an additional layer, such as a protective film, can be formed on the negative electrode active material layer.

[0122] For example, the negative electrode active material layer can be formed by coating a negative electrode active material slurry containing a mixture of negative electrode active material, binder, and conductive material dissolved or dispersed in a solvent onto a negative electrode current collector, followed by drying and pressing. If desired, the mixture may further include dispersants, fillers, or optional additives thereof.

[0123] (Negative electrode active material)

[0124] The negative electrode active material can include compounds capable of reversibly inserting / deintercalating lithium ions. Specific particles of the negative electrode active material include, but are not limited to: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; silicon-based materials, such as silicon powder, amorphous silicon, silicon nanofibers, and silicon nanowires; silicon compounds, such as silicon alloys, silicon oxides, and alkali metal or alkaline earth metal-doped silicon oxides; metallic materials capable of alloying with lithium, such as Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Sn alloys, Al alloys, etc.; metal oxides capable of doping / dedoping lithium, such as SnO2, vanadium oxides, and lithium vanadium oxides; composite materials of silicon-based materials and carbonaceous materials, or other composite materials, such as Sn-C composite materials, etc. This negative electrode active material can be used alone or in combination. Meanwhile, carbonaceous materials can include low-crystallinity carbon or high-crystallinity carbon. Low-crystallinity carbon includes soft carbon and hard carbon. Highly crystalline carbon includes amorphous, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature calcined carbon, such as petroleum / coal-based coke.

[0125] Based on the total weight of the negative electrode active material layer, the amount of negative electrode active material can be from 80% to 99% by weight.

[0126] (Adhesives and conductive materials)

[0127] The type and content of the binder and conductive material used in the negative electrode slurry can be the same as those described for the positive electrode above.

[0128] (solvent)

[0129] There are no particular restrictions on the solvents used in the negative electrode slurry, as long as they are conventionally used in the manufacture of the negative electrode. Specific examples of solvents include, but are not limited to: N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropanol, acetone, water, etc. Such solvents can be used alone or in combination.

[0130] [Method for manufacturing the negative electrode]

[0131] According to embodiments of this disclosure, similar to the method for manufacturing a positive electrode, a method for manufacturing a negative electrode for a lithium-ion secondary battery may include the following steps: dissolving or dispersing a negative electrode active material, optionally with a binder, a conductive material, etc., in a solvent to obtain a negative electrode slurry; and, for example, forming a negative electrode active material layer on a negative electrode current collector by coating the negative electrode slurry onto the negative electrode current collector to obtain a negative electrode.

[0132] [Septum]

[0133] In the lithium-ion secondary battery of the embodiments of this disclosure, the separator serves to separate the negative and positive electrodes from each other and provide a transport channel for lithium ions. Any separator can be used without particular limitation, as long as it is commonly used as a separator in a lithium-ion secondary battery. In particular, the separator preferably exhibits low resistance to electrolyte ion migration and high wettability to the electrolyte. Specific examples of separators may include porous polymer membranes, such as porous polymer membranes made of polyolefin polymers (including ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers), or laminates of two or more such porous polymer membranes. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, separators coated with ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength.

[0134] [Non-aqueous electrolytes]

[0135] In the lithium-ion secondary batteries of the embodiments of this disclosure, the non-aqueous electrolyte may include, but is not limited to, organic liquid electrolytes or inorganic liquid electrolytes that can be used to manufacture secondary batteries. For example, a solid electrolyte may be used.

[0136] Non-aqueous electrolytes may include organic solvents and lithium salts, and may further include additives if desired. In the following text, liquid electrolytes are also referred to as “electrolytes”.

[0137] There are no particular limitations on organic solvents, as long as they can serve as a medium for ion transport in the electrochemical reactions of the battery. Specific examples of organic solvents include, but are not limited to: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether and tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic hydrocarbon solvents, such as benzene or fluorobenzene; carbonate 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 solvents, such as ethanol and isopropanol; nitrile solvents, such as R-CN (where R is a straight-chain, branched, or cyclic C2-C20 hydrocarbon group, which may optionally contain a double-bonded aromatic ring or ether bond); amide solvents, such as dimethylformamide; dioxolane solvents, such as 1,3-dioxolane; or sulfone solvents, etc. Such solvents can be used alone or in combination. In particular, carbonate solvents are preferred. Furthermore, a mixture capable of enhancing the charge / discharge characteristics of the battery is more preferred, wherein the mixture comprises cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate). In this case, excellent electrolyte quality can be achieved when the cyclic carbonate and linear carbonate are mixed in a volume ratio of about 1:1 to 1:9.

[0138] There are no particular limitations on lithium salts, as long as they are compounds capable of providing lithium ions for lithium-ion secondary batteries. Specific examples of lithium salts include, but are not limited to: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. Such lithium salts can be used alone or in combination. For example, the concentration of lithium salts in the electrolyte can be from 0.1 mol / L to 2 mol / L. When the concentration of lithium salts falls within the above-defined range, the electrolyte exhibits suitable conductivity and viscosity and demonstrates excellent electrolyte quality, thus enabling efficient transport of lithium ions.

[0139] Electrolyte additives can be optionally used to improve battery life characteristics, thereby suppressing battery capacity degradation and improving battery discharge capacity. Specific examples of additives include, but are not limited to: alkyl halogenated carbonate compounds, such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); pyridine; triethyl phosphite; triethanolamine; cyclic ethers; ethylenediamine; n-glycol dimethyl ether; triammonium hexaphosphate; nitrobenzene derivatives; sulfur; quinone imine dyes; N-substituted oxazolidinones; N,N-substituted imidazolidinyl ethers; ethylene glycol diallyl ether; ammonium salts; pyrrole; 2-methoxyethanol; aluminum trichloride, etc. Such additives can be used alone or in combination. In this case, the amount of additive used can be from 0.1% by weight to 15% by weight, based on the total weight of the electrolyte.

[0140] [Manufacturing method of lithium-ion secondary batteries]

[0141] The lithium-ion secondary battery of the present disclosure can be obtained by providing a separator and an electrolyte between the positive and negative electrodes obtained as described above. Specifically, the lithium-ion secondary battery can be obtained by providing a separator between the positive and negative electrodes to form an electrode assembly, introducing the electrode assembly into a battery casing (e.g., a cylindrical or prismatic battery casing), and injecting an electrolyte. In one variation, after stacking the electrode assembly, an electrolyte is injected therein, and the resulting structure is introduced into a battery casing, followed by sealing.

[0142] The battery casing can be any type conventionally used in the art. For example, the shape of the battery casing can include a cylindrical, prismatic, pouch-like, or coin-like shape, similar to a can.

[0143] The lithium-ion secondary batteries of this disclosure can be used as power sources for small devices, or as unit cells in large and medium-sized battery modules comprising multiple battery cells. Examples of such large and medium-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0144] Example

[0145] The present disclosure will now be described in more detail with reference to embodiments and comparative examples. However, the scope of the present disclosure is not limited thereto. The mechanisms described below are for illustrative purposes only, and the scope of the present disclosure is not limited thereto.

[0146] [Example 1-1]

[0147] (Added iodine and boron)

[0148] First, 100 parts by weight of LiNi 0.90 Co 0.07 Mn 0.03Add 1.0 part by weight of iodine powder (I2, available from Fuji Film Wakou Pharmaceuticals) and 0.3 parts by weight of boric acid (H3BO3, available from Fuji Film Wakou Pharmaceuticals) to O2 (hereinafter also referred to as "lithium transition metal oxide") powder, seal the resulting mixture in a plastic bottle, and shake the plastic bottle up and down in your hand for about 1 minute to mix the ingredients, thereby providing the mixture.

[0149] (Firing)

[0150] The resulting mixture was heated to 350°C under ambient atmosphere, allowed to stand at 350°C for 5 hours for calcination, and then cooled to room temperature to obtain the positive electrode active material.

[0151] (Preparation of positive electrode active material slurry)

[0152] Then, 1.5 parts by weight of carbon black as a conductive material and 2.0 parts by weight of polyvinylidene fluoride (PVDF) as a binder are added together with 96.5 parts by weight of positive electrode active material to N-methyl-2-pyrrolidone (NMP) as a solvent and mixed to obtain a positive electrode active material slurry.

[0153] (Manufacturing of the positive electrode)

[0154] Then, the obtained positive electrode active material slurry is coated onto an aluminum foil with a thickness of 20 μm to about 70 μm and dried at 130°C to obtain a positive electrode sheet.

[0155] (Preparation of electrolytes)

[0156] An electrolyte is prepared by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:2:1, adding 2.0% by weight of ethylene carbonate (VC), and dissolving LiPF6 in the mixture at a concentration of 1 mol / L.

[0157] (Manufacturing of coin cells)

[0158] The obtained positive electrode sheet was stamped into a circle with a diameter of 13 mm to prepare the positive electrode. A lithium metal with a thickness of 0.3 mm was used as the negative electrode, and the electrolyte prepared above was used to obtain a CR2016 type coin cell.

[0159] (Manufacturing of a single battery)

[0160] Unlike coin cells, the positive electrode sheet obtained above is stamped into a square shape and used as the positive electrode, graphite of a corresponding size is used as the negative electrode, and an electrolyte prepared as described above is used to obtain a single cell.

[0161] [Examples 1-2]

[0162] Except that a mixture of 1.5 parts by weight of carbon black and carbon nanotubes was used instead of 1.5 parts by weight of carbon black as the conductive material, coin cells and single cells were obtained in the same manner as in Examples 1-1.

[0163] [Example 2]

[0164] Except for the addition of 0.5 parts by weight of boric acid, coin cells and single cells were obtained in the same manner as in Examples 1-1.

[0165] [Comparative Example 1-1]

[0166] Except for omitting the steps of adding iodine and boron and the firing step, coin cells and single cells were obtained in the same manner as in Examples 1-1. In other words, LiNi was used. 0.90 Co 0.07 Mn 0.03 O2 itself is used as the positive electrode active material, and no iodine or boric acid is added.

[0167] [Comparative Examples 1-2]

[0168] Except that a mixture of 1.5 parts by weight of carbon black and carbon nanotubes was used instead of 1.5 parts by weight of carbon black as the conductive material, coin cells and single cells were obtained in the same manner as in Comparative Example 1-1.

[0169] [Comparative Example 2-1]

[0170] Coin cells and single cells were obtained in the same manner as in Examples 1-1, except that only 1.0 part by weight of iodine was added without the addition of boric acid.

[0171] [Comparative Example 2-2]

[0172] Except that a mixture of 1.5 parts by weight of carbon black and carbon nanotubes was used instead of 1.5 parts by weight of carbon black as the conductive material, coin cells and single cells were obtained in the same manner as in Comparative Example 2-1.

[0173] [Comparative Example 3-1]

[0174] Coin cells and single cells were obtained in the same manner as in Examples 1-1, except that only 0.3 parts by weight of boric acid was added without the addition of iodine.

[0175] [Comparative Example 3-2]

[0176] Except that a mixture of 1.5 parts by weight of carbon black and carbon nanotubes was used instead of 1.5 parts by weight of carbon black as the conductive material, coin cells and single cells were obtained in the same manner as in Comparative Example 3-1.

[0177] [Comparative Example 4]

[0178] Coin cells and single cells were obtained in the same manner as in Examples 1-1, except that only 0.5 parts by weight of boric acid was added without the addition of iodine.

[0179] The conditions used in the various embodiments and comparative examples are shown in Table 1 below. The amounts of the positive electrode active material, conductive material, and binder are expressed in parts by weight, and the amounts of the conductive material and binder are expressed as parts by weight based on 96.5 parts by weight of the positive electrode active material.

[0180] [Table 1]

[0181]

[0182] [Test Example 1: Elemental Analysis of Cathode Active Materials Based on X-ray Fluorescence Spectroscopy]

[0183] Elemental analysis of the positive electrode active materials obtained in each example and comparative example was performed using X-ray fluorescence spectrometry (XRF). The XRF instrument was a scanning X-ray fluorescence spectrometer (ZSX Primus II, available from Rigaku). The samples analyzed by XRF before preparing the positive electrode active material slurry were solid positive electrode active materials. Using each value obtained from Comparative Example 1-1 (which had never undergone coating treatment) as a baseline, the iodine and boron contents of each sample were determined by subtracting the baseline values ​​from each measurement result of Examples 1-1 and 2. The results are shown in Table 2 below. Meanwhile, since the detection rate of boron by X-ray fluorescence spectrometry is low, the boron content values ​​are reference values.

[0184] [Table 2]

[0185] Example 1-1 0.1006% by weight 0.321% by weight Example 2 0.125% by weight 0.511% by weight

[0186] [Test Example 2: X-ray photoelectron spectroscopy (XPS) analysis of positive electrode active materials]

[0187] X-ray photoelectron spectroscopy (XPS) was used to analyze the various positive electrode active materials obtained in Examples 1-1 and Comparative Examples 1-1. The samples to be analyzed were solid positive electrode active materials obtained after sintering and before the preparation of the positive electrode active material slurry. Charge correction was performed on the positive electrode active materials derived from -(CH2). n The C1s peak energy was determined to be 284.6 eV.

[0188] Figure 1 Partial XPS spectra of Example 1-1 (solid line) and Comparative Example 1-1 (dashed line) are shown. In the case of the positive electrode active material of Example 1-1, iodine-derived 3d... 5 / 2The peaks observed were for electrons, but no peaks were observed in the positive electrode active material of Comparative Example 1-1. The peak positions are close to those of iodine-containing sodium iodate (NaIO3) or lithium iodate (LiIO3) with an oxidation state of +5, and iodine-containing sodium periodate (NaIO4) or lithium periodate (LiIO4) with an oxidation state of +7. Therefore, it is believed that the positive electrode active material at least partially contains iodine with a positive oxidation state. In particular, it is believed that the iodine in the positive electrode active material exists at least partially in the form of iodate ions and / or periodate ions. Meanwhile, in the case of Example 1-1, no peaks originating from iodine with an oxidation state of 0 or -1 were observed in the range of 618 eV to 620 eV.

[0189] Regarding boron, such as Figure 2 As shown, a peak originating from iodine B1s electrons with a peak at approximately 191.5 eV was observed in the range of 195.0 eV to 188.5 eV, while no peak was observed in the positive electrode active material of Comparative Example 1-1. The peak position is close to that of lithium metaborate (LiBO2). Therefore, it is believed that the positive electrode active material at least partially contains trivalent boron.

[0190] [Test Example 3-1: Initial Charge / Discharge Characteristics]

[0191] The coin batteries obtained in the examples and comparative examples were repeatedly subjected to charge / discharge cycles in a thermostat maintained at 25°C or 45°C, with a charging cutoff voltage of 4.25V, a discharging cutoff voltage of 3V, a charging current rate of 0.3C, and a discharging current rate of 0.3C. The charging capacity and discharging capacity of the first charge / discharge cycle were determined.

[0192] As shown in the formula below, the initial charge capacity is determined by dividing the charge capacity value of the first charge / discharge cycle by the weight of the positive electrode active material powder. Similarly, the initial discharge capacity is determined by dividing the discharge capacity value of the first charge / discharge cycle by the weight of the positive electrode active material powder. Furthermore, the initial efficiency is determined by the ratio of discharge capacity to charge capacity during the first charge / discharge cycle. Based on the determined charge and discharge capacities, the initial charge capacity, initial discharge capacity, and initial efficiency at 25°C, and the initial discharge capacity at 45°C are calculated.

[0193] [Mathematical Expression 1]

[0194] Initial charge capacity (mAh / g) = Charge capacity of the first charge / discharge cycle (mAh) / Weight of positive electrode active material (g)

[0195] [Mathematical Expression 2]

[0196] Initial discharge capacity (mAh / g) = Discharge capacity of the first charge / discharge cycle (mAh) / Weight of positive electrode active material (g)

[0197] [Mathematical Expression 3]

[0198] Initial efficiency (%) = Discharge capacity of the first charge / discharge cycle (mAh) / Charge capacity of the first charge / discharge cycle (mAh)

[0199] [Test Example 3-2: DC Resistance (DCR) Characteristics]

[0200] After the first and 30th charge cycles, the DC resistance (DCR) values ​​of the coin cells obtained in each embodiment and comparative example were measured. Specifically, the DC resistance value was calculated from the slope of a linear graph plotted using approximate values ​​of the discharge curve obtained by measuring voltage values ​​acquired over a predetermined 60-second time interval after discharge began, following a fully charged state. The DC resistance at the end of the first charge cycle was defined as the "initial DC resistance." Furthermore, the ratio of the DC resistance determined by the following formula was calculated.

[0201] [Mathematical Expression 4]

[0202] The ratio of DC resistance = DC resistance after the first charging cycle / DC resistance after the 30th charging cycle

[0203] (Results of examples and comparative examples without the addition of carbon nanotubes)

[0204] Table 3 below shows the results of tests 3-1 and 3-2 conducted in Examples 1-1 and 2 and Comparative Examples 1-1, 2-1, 3-1 and 4. The results in Table 3 include the initial charge capacity, initial discharge capacity and initial efficiency at 25°C, the initial discharge capacity at 45°C, and the ratio of initial DC resistance to DC resistance. It should be noted that the results in Table 3 are described as relative values ​​calculated by dividing actual values ​​by the corresponding values ​​in Comparative Example 1-1. In the "Iodine" and "Borate" columns, the weight parts of iodine and borate added per 100 parts by weight of lithium transition metal oxide are described, respectively.

[0205] [Table 3]

[0206]

[0207] As shown in Table 3, in terms of initial discharge capacity and initial efficiency, Comparative Examples 2-1 (with only iodine) and 3-1 (with only boric acid) did not provide any improvement compared to Comparative Example 1-1 (without iodine and boric acid). Comparative Example 4 (with only 0.5 parts by weight of boric acid) showed a slight improvement. Meanwhile, Examples 1-1 and 2 (with iodine and boric acid) showed significant improvements in initial discharge capacity and initial efficiency compared to Comparative Example 4.

[0208] As shown in Table 3, Comparative Examples 3-1 and 4, with the addition of boric acid, showed a significant improvement in initial DC resistance. Conversely, Examples 1-1 and 2, with the addition of both iodine and boric acid, suppressed the increase in initial DC resistance compared to Comparative Examples 3-1 and 4. In particular, Example 1-1 suppressed the increase in initial DC resistance compared to Comparative Example 2-1, with the addition of only iodine, and Example 2 also suppressed the increase in DC resistance to the same level as Comparative Example 2-1.

[0209] (Results of examples and comparative examples with added carbon nanotubes)

[0210] Table 4 below shows the results for Test Examples 3-1 and 3-2 for Examples 1-2 and Comparative Examples 1-2, 2-2, and 3-2. The results in Table 4 include the initial charge capacity, initial discharge capacity, and initial efficiency at 25°C, the initial discharge capacity at 45°C, and the ratio of initial DC resistance to DC resistance. It should be noted that the results in Table 4 are described as relative values ​​calculated by dividing actual values ​​by the corresponding values ​​in Comparative Examples 1-2. In the "Iodine" and "Borate" columns, the weight parts of iodine and borate added per 100 parts by weight of lithium transition metal oxide are described, respectively.

[0211] [Table 4]

[0212]

[0213] As shown in Table 4, in terms of initial discharge capacity and initial efficiency, Comparative Examples 2-2 (with only iodine) and 3-2 (with only boric acid) showed some improvement compared to Comparative Example 1-1 (without iodine and boric acid). Meanwhile, Examples 1-2 (with iodine and boric acid) showed a significant improvement in initial discharge capacity and initial efficiency compared to Comparative Examples 2-2 and 3-2.

[0214] As shown in Table 4, Comparative Example 3-2, with the addition of boric acid, showed a significant increase in initial DC resistance, but Examples 1-2 suppressed the increase in initial DC resistance compared to Comparative Example 3-2. Furthermore, Examples 1-2 suppressed the increase in initial DC resistance compared to Comparative Example 2-1, with the addition of iodine only.

[0215] The results from Test Examples 3-1 and 3-2 show that adding boric acid tends to increase initial capacity, initial efficiency, and initial DC resistance, while adding iodine does not provide the same level of increase in initial DC resistance as adding boric acid. Simultaneously, adding both iodine and boric acid improves initial capacity and initial efficiency while suppressing the increase in initial DC resistance. Since the initial DC resistance with both iodine and boric acid is lower than that with iodine alone, this indicates that the increase in DC resistance caused by boric acid is not suppressed by adding iodine alone. In other words, compared to cathode active materials using either iodine or boric acid, the simultaneous addition of iodine and boric acid provides cathode active materials exhibiting higher quality in both capacity and resistance characteristics.

[0216] [Test Example 4-1: Capacity Retention]

[0217] The single cells obtained in each embodiment and comparative example were aged at 25°C with a charging current rate of 0.1C and a discharging current rate of 0.1C. Then, the single cells were repeatedly charged / discharged in a thermostat maintained at 45°C under conditions of a charging cutoff voltage of 4.2V, a discharging cutoff voltage of 2.5V, a charging current rate of 0.3C, and a discharging current rate of 0.3C. The capacity retention rate after n repeated charge / discharge cycles, as determined by the following mathematical formula 5, is calculated from the discharge capacity of each charge / discharge cycle:

[0218] [Mathematical Expression 5]

[0219] Capacity retention rate (%) = {(Discharge capacity in the nth charge / discharge cycle) / (Discharge capacity in the 1st charge / discharge cycle)} × 100%

[0220] [Test Example 4-2: Linear Resistance Increase Rate]

[0221] The DC resistance value of the single battery in each charge / discharge cycle was determined in the same manner as in Test Example 3-2. The linear resistance increase rate at the nth charge / discharge cycle was calculated based on the determined DC resistance value. The linear resistance increase rate in Examples 1-1 and 2, and Comparative Examples 1-1, 2-1, 3-1, and 4 was determined according to the following mathematical formula 6. To facilitate comparison of the changes in linear resistance between the various examples and comparative examples, the linear resistance increase rate of Comparative Example 1-1 at the 299th cycle was normalized with reference to it.

[0222] [Mathematical Expression 6]

[0223] The rate of increase in linear resistance (%) = [{(linear resistance of the nth charge / discharge cycle) / (linear resistance of the 1st charge / discharge cycle)} / {(linear resistance of the 299th charge / discharge cycle in Comparative Example 1-1) / (linear resistance of the 1st charge / discharge cycle in Comparative Example 1-1)}] × 100%

[0224] The linear resistance increase rate in Examples 1-2 and Comparative Examples 1-2, 2-2, and 3-2 was determined according to the following mathematical formula 7. To facilitate comparison of the changes in linear resistance between the various examples and comparative examples, the linear resistance increase rate of Comparative Example 1-2 in the 299th cycle was normalized with reference to it.

[0225] [Mathematical Expression 7]

[0226] The rate of increase in linear resistance (%) = [{(linear resistance of the nth charge / discharge cycle) / (linear resistance of the 1st charge / discharge cycle)} / {(linear resistance of the 299th charge / discharge cycle in Comparative Example 1-2) / (linear resistance of the 1st charge / discharge cycle in Comparative Example 1-2)}] × 100%

[0227] (Results of examples and comparative examples without the addition of carbon nanotubes)

[0228] Figure 3 The graph illustrates the battery capacity changes during the 1st to 50th charge-discharge cycles in Examples 1-1 and 2, and Comparative Examples 1-1, 2-1, 3-1, and 4, by plotting the capacity retention rate as a function of the cycle number as defined above. The discharge capacity of each example and comparative example in the first cycle is considered to be 100%. Regarding battery capacity degradation, the degradation in Comparative Examples 3-1 and 4 is relatively significant, while the degradation in Examples 1-1 and 2 and Comparative Example 2-1 is relatively insignificant. In the cases of Comparative Examples 1-1 and 3-1, the capacity retention rate changes significantly, with a high amplitude as a function of cycle number. Figure 3 In this study, the results of the first to the 50th charge / discharge cycles were amplified to facilitate the identification of this change.

[0229] Figure 4 The graphs showing the DC resistance changes during the 1st to 200th charge-discharge cycles in Examples 1-1 and 2, and Comparative Examples 1-1, 2-1, 3-1, and 4, are illustrated by plotting the linear resistance increase rate as a function of the cycle number as defined above. When the charge / discharge cycles were repeated, all examples and comparative examples showed an increase in the linear resistance value. Regarding the linear resistance increase rate, Example 1-1 showed the smallest linear resistance increase rate, and Example 2 showed the second smallest. Meanwhile, Comparative Example 1-1 showed the largest linear resistance increase.

[0230] (Results of examples and comparative examples with added carbon nanotubes)

[0231] Figure 5 The graph illustrates the battery capacity changes during the 1st to 50th charge-discharge cycles in Examples 1-2 and Comparative Examples 1-2, 2-2, and 3-2 by plotting the capacity retention rate as a function of the cycle number, as defined above. The discharge capacity in the first cycle of each example and comparative example was taken as 100%. Regarding battery capacity degradation, the degradation in Comparative Examples 1-2 and 3-2 was relatively significant, while the degradation in Examples 1-2 and Comparative Examples 2-2 was relatively insignificant. In the cases of Comparative Examples 1-2 and 3-2, the capacity retention rate changed significantly, with a high amplitude as a function of cycle number.

[0232] Figure 6 The graph shows the change in DC resistance during the 1st to 200th charge / discharge cycles in Examples 1-2 and Comparative Examples 1-2, 2-2, and 3-2, by plotting the linear resistance increase rate as defined above as a function of the number of cycles. Figure 4 Similarly, when repeated charge / discharge cycles were performed, all embodiments and comparative examples showed an increase in linear resistance value. Regarding the rate of increase in linear resistance, Embodiments 1-2 showed the smallest rate of increase in linear resistance, while Comparative Examples 1-2 showed the largest rate of increase in linear resistance.

[0233] [Test Example 5: Impedance after repeated charge / discharge]

[0234] In the charge / discharge repetition test of Test Example 4, the impedance of the single cells obtained in Examples 1-1 and 1-2 and Comparative Examples 1-1, 1-2, 2-1, 2-2, 2-1, and 3-2 was measured using an impedance analyzer after the completion of the first charge cycle and after the completion of the 299th charge cycle. The impedance of each negative electrode was calculated based on the negative electrode impedance component appearing on the high-frequency side (1,000,000 Hz to 100 Hz) of the obtained Cole-Cole plot. Similarly, the impedance of each positive electrode was calculated based on the positive electrode impedance component appearing on the low-frequency side (100 Hz to 0.01 Hz) of the obtained Cole-Cole plot. The results are shown in Table 5 below. In Table 5, the impedance is expressed as a relative value (relative impedance) based on the impedance value of Comparative Example 1-1 after the first or 299th cycle. Meanwhile, in the "Iodine and Boron" column, the case of adding only iodine is indicated by "I", the case of adding only boron is indicated by "B", the case of adding both iodine and boron is indicated by "I, B", and the case of not adding iodine and boron is indicated by "-".

[0235] [Mathematical Expression 8]

[0236] Relative impedance = Measured impedance / Impedance of Comparative Example 1-1

[0237] [Table 5]

[0238]

[0239] First, Examples 1-1 and Comparative Examples 1-1, 2-1, and 3-1, which do not use carbon nanotubes as the conductive material, are discussed. When comparing Comparative Example 1-1 without iodine and boron and Comparative Example 2-1 with only iodine, the initial impedance after the first charge did not change significantly due to the addition of iodine. However, after repeated charge / discharge cycles, the impedance on the low-frequency side decreased significantly. Simultaneously, comparing Comparative Example 1-1 without iodine and boron with Comparative Example 3-1 with only boron, the initial impedance on the low-frequency side after the first charge increased significantly due to the addition of boron. However, after repeated charge / discharge cycles, the impedance on the high-frequency side decreased significantly, and the impedance on the low-frequency side also decreased to a value equivalent to that of Comparative Example 1-1. Therefore, this indicates that adding iodine is effective in reducing the impedance on the low-frequency side (positive electrode side), and adding boron is effective in reducing the impedance on the high-frequency side (negative electrode side). In Example 1-1, where iodine and boron are added simultaneously, the effect of reducing the impedance on the low-frequency side (positive electrode side) can be balanced with the effect of reducing the impedance on the high-frequency side (negative electrode side). Furthermore, in the case of Example 1-1, the significant increase in the initial impedance on the low-frequency side caused by the addition of boron can be suppressed.

[0240] Next, when comparing Examples 1-2 and Comparative Examples 1-2, 2-2, and 3-2 using carbon nanotubes as conductive materials, a trend substantially the same as that without carbon nanotubes was observed. Furthermore, when comparing Examples 1-1 and 1-2 with and without carbon nanotubes, it can be seen that both the impedance on the high-frequency side and the impedance on the low-frequency side decreased before and after charge / discharge cycles.

[0241] [Reference Example 1]

[0242] Figure 7 The diagram shows the process of obtaining I3d by mixing orthoperiodic acid (H5IO6) as a coating component with lithium transition metal oxide and calcining the resulting mixture at 350°C for 5 hours. 5 / 2 XPS spectrum. From Figure 7It can be seen that when H5IO6 is used as the iodine-based coating material, the same spectrum as in Example 1-1, which uses elemental iodine as the coating material, can be obtained. Meanwhile, the original periodic acid (H5IO6) melts at 132°C and begins to dehydrate to produce metaperiodic acid (HIO4). Furthermore, iodine (V) oxides such as I2O4 or I2O5 decompose into oxygen and iodine above 275°C. Based on the above, it is assumed that regardless of the valence of iodine in the coating composition (i.e., even if metaperiodic acid (HIO4), I2O4, or I2O5 is used as the coating material), iodine, after being mixed with lithium transition metal oxides and calcined, has the same oxidation state as in Example 1-1, which uses elemental iodine.

Claims

1. A positive electrode active material, comprising: A core containing lithium transition metal oxides; and The coating portion, which at least partially covers the surface of the core and contains iodine and boron, in, The coated portion contains iodine with an oxidation state of +5 to +7. Of which, based on 100 parts by weight of lithium transition metal oxide, the iodine content is from 0.001 parts by weight to 5 parts by weight, and Of which, based on 100 parts by weight of lithium transition metal oxide, the boron content is from 0.001 parts by weight to 5 parts by weight.

2. The positive electrode active material as described in claim 1, wherein, The coating contains iodine with an oxidation state of +7.

3. The positive electrode active material as described in claim 1, wherein, I3d observed by X-ray photoelectron spectroscopy of the positive electrode active material 5 / 2 The spectrum has peaks in the range of 623.5 eV to 624.5 eV.

4. The positive electrode active material as described in claim 1, wherein, Based on 100 parts by weight of lithium transition metal oxide, the iodine content is from 0.005 parts by weight to 2 parts by weight.

5. The positive electrode active material as described in claim 1, wherein, Based on 100 parts by weight of lithium transition metal oxide, the boron content is from 0.01 parts by weight to 3 parts by weight.

6. A positive electrode active material slurry for lithium-ion secondary batteries, comprising the positive electrode active material according to any one of claims 1 to 5.

7. A positive electrode for a lithium-ion secondary battery, having a positive electrode active material layer comprising the positive electrode active material according to any one of claims 1 to 5, and formed on a current collector.

8. The positive electrode as described in claim 7, wherein, The positive electrode active material layer further includes a conductive material comprising carbon nanotubes.

9. A lithium-ion secondary battery comprising the positive electrode as described in claim 7 or 8.

10. A method for preparing a positive electrode active material, wherein the positive electrode active material is as described in any one of claims 1 to 5, the method comprising the following steps: Preparation of a mixture comprising lithium transition metal oxide, iodine, and boron; and The mixture is then calcined.

11. The method for preparing a positive electrode active material as described in claim 10, further comprising the step of adding an iodine-containing component as a component of the mixture. in, The iodine component includes at least one 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 iodate (LiIO3), sodium iodate (NaIO3), potassium iodate (KIO3), ammonium iodate (NH4IO3), metaperiodic acid (HIO4), orthoperiodic acid (H5IO6), lithium periodate (LiIO4), sodium periodate (NaIO4), potassium periodate (KIO4), iodine oxide (IV) (I2O4), iodine oxide (V) (I2O5), and iodine oxide (IV, V) (I4O9).

12. The method for preparing a positive electrode active material as described in claim 10 or 11, comprising the step of adding a boron-containing boron component as a component of the mixture. in, The boron component includes those selected from H3BO3, HBO2, B2O3, LiBO2, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, and C. 13 H 19 At least one of the group consisting of BO3, C3H9B3O6 and (C3H7O)3B.

13. The method for preparing a positive electrode active material as described in claim 10 or 11, comprising the step of calcining the mixture at a calcination temperature of 150°C to 500°C.

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