JP2023162559A - Lithium composite oxide and method for producing the same - Google Patents

Abstract

To provide a lithium composite oxide for meeting the demand for improved cycle stability and obtaining a positive electrode active material for a lithium-ion battery excellent in electrochemical characteristics, and to provide a method for producing the same.SOLUTION: A lithium composite oxide having a composition formula LixPyMezMn1-zO2 (where 0<x≤1.3, 0<y≤0.1, 0<z≤0.2), where Me is one or more metallic elements selected from the group consisting of Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, Zn, and Zr, and having a rectangular zigzag layered structure as a base structure, a domain of monoclinic or rhombohedral α-NaFeO2 type layered structure, an intensity ratio (A/B) of a diffraction peak integrated intensity (A) observed at 15.3±1.0° to a diffraction peak integrated intensity (B) observed at 18.2±1.0° in powder X-ray diffraction that is 0.5 or more, and a BET specific surface area of 3.5 to 15 m2/g, and a method for producing the same, are provided.SELECTED DRAWING: None

Description

The present invention relates to a lithium composite oxide and a method for producing the same, and more particularly to a lithium composite oxide substituted with a different metal that has improved output characteristics and a method for producing the same.

Lithium composite oxide is generally used as a positive electrode active material for lithium ion batteries. Lithium composite oxides, specifically lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), etc., are the positive electrode active materials of lithium ion batteries that are distributed all over the world. It is often used as Active research is being conducted to improve the characteristics (higher capacity, higher output, cycle stability) and safety of such lithium composite oxides.

Li _x Ni _1-y-z Co _y consisting of lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn) and oxygen (O) is suitable as a positive electrode active material for lithium-ion batteries suitable for these goals. LixNi _1-yz Co _{y Al z} O ₂ (NCA) consisting of Mn z O 2 (NCM), _Li , Ni, Co, aluminum (Al) and O is used. These materials use less Co than existing lithium composite oxides to improve safety, use cheaper metals, and have discharge capacities of approximately 165 mAh/g for NCM and 200 mAh/g for NCA, compared to LiCoO ₂ Achieved higher capacity.

In order to improve the performance of such lithium ion batteries, increased capacity is attracting particular attention, and lithium is expressed by LiMnO ₂ and has a crystal structure with a zigzag layered structure as a mother structure and domains with an α-NaFeO ₂ type layered structure. A composite oxide has been disclosed as a high capacity material (see Patent Document 1).

LiMnO ₂ characterized by being composed of one or more of rectangular crystals and monoclinic crystals has been disclosed, and its discharge capacity was low at about 170 mAh/g. The crystal structure was modified through the process, and the material was further improved as a positive electrode active material with a high discharge capacity of 260 mAh/g. Although such LiMnO ₂ has been found to be a positive electrode active material for lithium ion secondary batteries that has a high capacity and is inexpensive, it has a problem of low output characteristics.

In view of the problem of low output characteristics, we produced a metal composite oxide in which a different metal element was substituted for a manganese compound, mixed it with a lithium compound and sintered it, and changed the crystal structure from the existing LiMnO ₂ to improve output. A lithium composite oxide with improved properties has been disclosed (see Patent Document 2). However, this dissimilar metal-substituted lithium composite oxide has a problem of low cycle stability.

In view of the problem of low cycle stability, the present invention creates a lithium composite oxide that improves cycle stability compared to existing dissimilar metal-substituted lithium composite oxides by adding and mixing lithium phosphate to a lithium composite oxide. and its manufacturing method.

Japanese Patent Application Publication No. 2019-153564 JP 2021-183555 Publication

As electronic devices have recently become smaller and lighter, research into lithium-ion batteries has been progressing to develop batteries with superior electrochemical properties such as higher capacity, higher voltage, and higher output. In particular, as described in the Background Art section, improving the cycle stability of active materials is essential for practical use of positive electrode materials for lithium ion batteries.

The present invention aims to solve the demand for improved cycle stability, and provides a lithium composite oxide and a method for producing the same for obtaining a positive electrode active material for lithium ion secondary batteries with excellent electrochemical properties. It is in.

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, the gist of the present invention is as follows.

(1) Represented by the compositional formula Li _x P _y Me _z Mn _1-z O ₂ (0<x≦1.3, 0<y≦0.1, 0<z≦0.2), Me is one or more metal elements selected from the group consisting of Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, Zn, and Zr, and has a rectangular system. The integrated intensity of the diffraction peak observed at 15.3 ± 1.0° in powder X-ray diffraction, which has a zigzag layered structure as a parent structure and domains of monoclinic or rhombohedral α-NaFeO ₂ type layered structure. The intensity ratio (A/B) between (A) and the integrated intensity of the diffraction peak observed at 18.2±1.0° (B) is 0.5 or more, and the BET specific surface area is 3.5 to 15 m ² /g of lithium composite oxide.

(2) After assembling a carbon counter electrode cell and conducting a 100 cycle charge/discharge test at 25°C, 2.0-4.4V (vs. carbon electrode), and current density of 66 mA/g, the carbon negative electrode was taken out and dissolved in acid. The lithium composite oxide according to (1) above, wherein the amount of Mn precipitated when measured by an ICP method is 1.0 wt% or less based on the weight of Mn in the positive electrode active material.

(3) Compositional formula (Me _y Mn _1-y ) _a O _b (However, 1.3<a/b<1.6, 0<y≦0.2, and Me is Al, Co, Cr , Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, Zn, and Zr), and the average oxidation number of the metal ion is 2. A lithium composite oxide whose main phase is represented by Li _x Me _y Mn _1-y O ₂ having a zigzag layered structure is synthesized by mixing and sintering a manganese compound and a lithium compound with a molecular weight of 6 or more and 3.3 or less. , the lithium composite oxide according to (1) or (2) above, in which lithium phosphate is added to the obtained Li _x Me _y Mn _1-y O ₂ , subjected to mechanical milling, and then heat treated in an inert gas. manufacturing method.

(4) Composition formula (Me _y Mn _1-y ) _a O _b (However, 1.3<a/b<1.6, 0<y≦0.2, and Me is Al, Co, Cr , Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, Zn, and Zr), and the average oxidation number of the metal ion is 2. A lithium composite oxide whose main phase is represented by Li _x Me _y Mn _1-y O ₂ having a zigzag layered structure is synthesized by mixing and sintering a manganese compound and a lithium compound with a molecular weight of 6 or more and 3.3 or less. , the obtained Li _x Me _y Mn _1-y O ₂ is mechanically milled, then heat treated in an inert gas, lithium phosphate is added and mixed, and then heat treated again in an inert gas. The method for producing a lithium composite oxide according to 1) or (2).

(5) The metal composition is Me _y Mn _1-y (0<y≦0.2, and Me is Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V , W, Zn, and Zr) and a lithium compound are hydrothermally treated in an alkaline aqueous solution, resulting in Li _x Me _y Mn ₁ The method for producing a lithium composite oxide according to (1) or (2) above, which comprises adding and mixing lithium phosphate to the lithium composite oxide represented by _-y O ₂ and then heat-treating in an inert gas.

(6) The metal composition is Me _y Mn _1-y (0<y≦0.2, and Me is Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V , W, Zn, and Zr), a manganese compound, a lithium compound, and phosphoric acid are hydrothermally treated in an alkaline aqueous solution as described in (1) or (2) above. A method for producing lithium composite oxide.

(7) The metal composition is Me _y Mn _1-y (0<y≦0.2, and Me is Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V Li _x Me _y obtained by mixing a manganese compound Me _y Mn _1-y OOH (one or more metals selected from the group consisting of , W, Zn, and Zr) with lithium hydroxide and firing it. The lithium composite oxide according to (1) or (2) above, in which lithium phosphate is added to and mixed with the lithium composite oxide represented by Mn _1-y O ₂ and then heat-treated in an inert gas. manufacturing method.

(8) The metal composition is Me _y Mn _1-y (0<y≦0.2, and Me is Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V , W, Zn, and Zr) is mixed with the manganese compound Me _y Mn _1-y OOH, lithium phosphate, and lithium hydroxide, and fired. Or the method for producing a lithium composite oxide according to (2).

(9) An electrode containing the lithium composite oxide according to (1) or (2) above.

(10) A lithium ion secondary battery using the electrode described in (9) above as a positive electrode.

By controlling the BET specific surface area, the positive electrode active material using the lithium composite oxide of the present invention is expected to have high capacity and high output when applied to secondary batteries. Furthermore, the compositing of phosphorus has the remarkable effect of improving cycle stability.

By applying such a positive electrode active material to a secondary battery, it is expected that a lithium ion secondary battery with high capacity and output and high cycle stability can be provided.

FIG. 2 is a schematic diagram showing a rectangular zigzag layered structure. It is a schematic diagram showing a layered structure (2a) and a rock salt type structure (2b). 3 is a diagram showing XRD patterns of lithium composite oxides of Examples 1 to 3 and Comparative Examples 1 and 2. FIG.

The present invention will be explained in detail below.

The lithium composite oxide of the present invention has a composition formula Li _x P _y Me _z Mn _1-z O ₂ (where 0<x≦1.3, 0<y≦0.1, 0<z≦0.2). ), in which manganese is substituted with a different metal and phosphorus is compounded.

The dissimilar metal Me is one or more metals selected from the group consisting of Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, Zn, and Zr; Among them, it is preferably one or more metals selected from the group consisting of Al, Co, Fe, Mg, Nb, Ni, Ti, and Zn. The amount of substitution of different metals is not particularly limited, but is preferably 20.0 mol% or less, more preferably 1.0 to 10.0 mol% of manganese.

The lithium composite oxide of the present invention has a parent structure having a rectangular zigzag layered structure and domains having a monoclinic or rhombohedral α-NaFeO ₂ type layered structure. By having a rectangular zigzag layered structure as the parent structure and domains of monoclinic or rhombohedral α-NaFeO ₂ type layered structure, no initial activation charge/discharge cycle is required and high capacity can be developed from the initial cycle. This is advantageous compared to rectangular LiMnO ₂ , which is activated and develops high capacity by charging and discharging several tens of cycles.

Here, the rectangular zigzag layered structure refers to belonging to the space group Pmnm. A schematic diagram of the rectangular zigzag layered structure is shown in FIG. Further, schematic diagrams of a layered structure and a rock salt structure, which are different from the rectangular zigzag layered structure, are shown in FIGS. 2(2a) and 2(2b), respectively. As can be seen from Figures 1 and 2, the rectangular zigzag layered structure is a crystal structure in which the layers in the α-NaFeO ₂ type layered structure grow vertically and regularly, forming a zigzag layered structure. .

A domain with a monoclinic or rhombohedral α-NaFeO ₂ type layered structure refers to a domain belonging to a space group C2/m, R-3m or Fm-3m, and a monoclinic or rhombohedral α-NaFeO ₂ Since the domain has a type layered structure, the rectangular crystal and the monoclinic crystal or the rhombohedral crystal form an intergrowth structure due to stacking faults.

The lithium composite oxide of the present invention has a diffraction peak integrated intensity (A) observed at 15.3±1.0° in powder X-ray diffraction under the following measurement conditions, and 18.2±1.0°. It is characterized in that the intensity ratio (A/B) to the observed diffraction peak integrated intensity (B) is 0.5 or more.

[Measurement condition]
・X-ray source: CuKα ray = 1.5418 Å
・Divergence slit: 1°
・Divergence vertical restriction slit: 10mm
・Scattering slit: Open ・Light receiving slit: Open ・Step width: 0.04°
・Scan speed: 4°/min

When the intensity ratio (A/B) is less than 0.5, the main phase is a monoclinic or rhombohedral α-NaFeO ₂ type layered structure, and the lithium composite oxide has a domain of a rectangular zigzag layered structure. Therefore, cycle deterioration may become large. The intensity ratio (A/B) is preferably 1.0 to 146.0, more preferably 2.6 to 33.6.

The BET specific surface area of the lithium composite oxide of the present invention is not particularly limited, but is preferably 2.0 m ² /g or more, more preferably 2.0 to 20.0 m ² /g. The BET specific surface area of lithium composite oxide is determined by converting the adsorption isotherm obtained from physical gas adsorption into a BET plot, determining the amount of gas adsorption Vm in a monomolecular layer based on the BET isotherm equation, and calculating the amount of gas adsorption Vm in the monomolecular layer based on the BET isotherm formula. It can be determined by the so-called BET method, which calculates the specific surface area based on the size.

The lithium composite oxide of the present invention has a compositional formula (Me _y Mn _1-y ) _a O _b (where 1.3<a/b<1.6, 0<y≦0.2, and Me is one or more metals selected from the group consisting of Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, Zn, and Zr), and the metal A manganese compound and a lithium compound whose average oxidation number of ions is 2.6 or more and 3.3 or less are mixed and sintered, and the main phase is represented by Li _x Me _y Mn _1-y O ₂ having a zigzag layered structure. It can be produced by synthesizing a lithium composite oxide, adding lithium phosphate to the obtained Li _x Me _y Mn _1-y O ₂ , subjecting it to mechanical milling, and then heat-treating it in an inert gas. .

Alternatively, the obtained lithium composite oxide represented by Li _x Me _y Mn _1-y O ₂ whose main phase has a zigzag layered structure is subjected to mechanical milling, then heat treated in an inert gas, and then lithium phosphate It is also possible to produce by adding and mixing, and then heat-treating again in an inert gas.

There are no particular restrictions on the metal raw materials used in manufacturing. Examples include sulfates, carbonates, nitrates, acetates, chlorides, hydroxides, oxidized salts, etc., but there is no limitation thereto.

In the production of the lithium composite oxide of the present invention, the manganese compound has the composition formula (Me _y Mn _1-y ) _a O _b (where 1.3<a/b<1.6, 0<y≦0.2 and Me is one or more metals selected from the group consisting of Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, Zn, and Zr). An aqueous solution of a metal salt of a substituent element and manganese is prepared in advance so that the average oxidation number of the metal ion is 2.6 or more and 3.3 or less, and a preferable Me/Mn molar ratio is obtained. For example, in the present invention, sulfide [(Me・Mn)(SO ₄ ) _a ], hydroxide [(Me・Mn)(OH) _b ], oxywater prepared in advance to have a preferable Me/Mn molar ratio Examples include oxides [(Me·Mn)(OOH) _c ] and oxides [(Me·Mn)O _d ], but there is no limitation to these. In the formula, a, b, c, and d are numerical values that satisfy the valence.

There are no particular restrictions on the metal raw materials used in the production, and examples include sulfates, carbonates, nitrates, acetates, chlorides, hydroxides, oxides, etc., but there are no limitations to these.

The above manganese compound becomes manganese oxide by sintering in air at 600 to 900°C for 12 to 24 hours.

If the average oxidation number of the metal ions in the manganese compound is less than 2.6, sintering in air will result in a Mn ₃ O ₄ attributed composition (Mn _y Me _1-y ) ₃ O ₄ , and 3. If it exceeds 3, the MnO ₂ attributed composition becomes Mn _y Me _1-y O ₂ . When these manganese compounds and lithium compounds are mixed and sintered, a lithium composite oxide whose main phase is represented by Li _x Me _y Mn _1-y O ₂ having a zigzag layered structure can be obtained, but it has a monoclinic or rhombic crystal structure. It does not have a domain with a hedral α-NaFeO ₂ type layered structure. Preparing in advance a metal salt aqueous solution of a substituent element and manganese so as to have a preferable Me/Mn molar ratio means to produce a manganese compound at a Me/Mn molar ratio according to the charged composition.

In the production of the lithium composite oxide of the present invention, the lithium compound to be mixed with the manganese compound is not particularly limited, but examples include lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, lithium chloride, lithium iodide, lithium oxalate, Examples include lithium sulfate and lithium oxide, but there is no limitation to these.

Sintering of the above-mentioned manganese compound and lithium compound is not particularly limited, but is preferably carried out at 700 to 1000°C for 6 to 24 hours in an inert gas, and mechanical milling is carried out, for example, at 300 to Preferably, the heating time is 800 rpm for 6 to 72 hours.

The above-mentioned mechanical milling is preferably carried out in an inert gas in a sealed container using a ball made of the same material as the container. The materials of the closed container and the ball are not particularly limited, and examples thereof include silicon nitride, zirconia, stainless steel, tungsten carbide, sintered alumina, etc., but there are no limitations to these materials.

The heat treatment subsequent to mechanical milling is performed in an inert atmosphere. Although the time and temperature are not particularly limited, for example, it is preferably 500 to 900°C for 1 to 24 hours, and more preferably 500 to 750°C for 1 to 12 hours.

The lithium composite oxide of the present invention has a metal composition of Me _y Mn _1-y (where 0<y≦0.2, and Me is Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni , Si, Ti, V, W, Zn, and Zr) and the above lithium compound are mixed and hydrothermally treated in an alkaline aqueous solution. It can be produced by adding and mixing lithium phosphate to the lithium composite oxide represented by Li _x Me _y Mn _1-y O ₂ and then heat-treating it in an inert gas. Alternatively, it can be produced by hydrothermally treating a manganese compound whose metal composition is Me _y Mn _1-y , a lithium compound, and phosphoric acid in an alkaline aqueous solution.

The alkaline aqueous solution in which the above hydrothermal treatment is performed refers to, for example, a mixed solution of lithium hydroxide and potassium hydroxide. The pH of the alkaline aqueous solution is preferably 11.0 to 14.0, for example.
The temperature of the above hydrothermal treatment is not particularly limited, but is preferably 140° C. or higher for 1 hour or more, and more preferably 180 to 240° C. for 4 to 24 hours.

In the above hydrothermal treatment, the mixing ratio of the manganese compound and the lithium compound (Li/Mn+Me) is not particularly limited, but it is preferably 1.5 or more, and more preferably 2.0 to 8.0.
The lithium composite oxide of the present invention has a metal composition of Me _y Mn _1-y (where 0<y≦0.2, and Me is Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni , Si, Ti, V, W, Zn, and Zr) obtained by mixing a manganese compound Me _y Mn _1-y OOH with lithium hydroxide and firing it. It can be produced by adding and mixing lithium phosphate to a lithium composite oxide represented by Li _x Me _y Mn _1-y O ₂ characterized by the following, and then heat-treating it in an inert gas. can. Alternatively, it can be produced by mixing a manganese compound Me _y Mn _{1- y} OOH whose metal composition is represented by Me _y Mn 1-y, lithium phosphate, and lithium hydroxide, and firing the mixture.

The electrode of the present invention is characterized by containing the lithium composite oxide of the present invention, and preferably contains a conductive material and a binder in addition to the lithium composite oxide.

The above-mentioned conductive material is added to improve the conductivity of the electrode. The conductive material is not particularly limited, and examples thereof include carbon blacks such as acetylene black and Ketjen black. From the viewpoint of improving the output characteristics of the battery, it is preferable to uniformly distribute the conductive material around the positive electrode active material to form a network through which electrons flow.

The content of the conductive material in the lithium composite oxide of the electrode of the present invention is not particularly limited, but is preferably 1 to 10% by weight.

Examples of the above binders include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinyl chloride (PVC), carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), etc. is exemplified, but there is no particular restriction.

The binder content in the electrode of the present invention is not particularly limited, but is preferably, for example, 1 to 10% by weight.

Examples of the structure of the lithium ion secondary battery other than the positive electrode include the following, but there are no particular limitations.

Examples of the negative electrode include materials that reversibly intercalate and release Li, such as carbon-based materials, tin oxide-based materials, silicon oxide-based materials, Li ₄ Ti ₅ O ₁₂ , and materials that form alloys with Li.

Examples of the electrolyte include an organic electrolyte in which Li salt and various additives are dissolved in an organic solvent, an ionic liquid, a solid electrolyte that conducts Li ions, and a combination thereof. The organic solvent of the electrolyte is not particularly limited, but examples include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), and examples of the electrolyte salt include , tetrafluoroborate (BF _4- ), hexafluorophosphate (PF _6- ), fluoromethanesulfonylimide (FSI _- ), trifluoromethanesulfonylimide (TFSI _- ), trifluoromethanesulfonate (CF ₃ SO _3- ), etc. is exemplified, but there is no particular restriction.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention should not be construed as being limited to these Examples.

<Confirmation of crystal structure>
The crystal structure of the lithium composite oxide was identified using powder XRD (trade name: Ultima IV, manufactured by Rigaku).
The measurement conditions were as follows.
・Target: Cu/Kα
・Output: 1.6kW (40mA-40kV)
・Data interval: 0.04° (2θ/θ)
・Measurement range: 10~90° (4°/min)

<Measurement of BET specific surface area>
0.2 g of the sample was placed in a glass cell for BET specific surface area measurement, and subjected to dehydration treatment at 150° C. for 30 minutes under nitrogen aeration to remove water adhering to the powder particles. The BET specific surface area of the treated sample was measured using a BET measurement device (trade name: MiCROMETRICS Desorb III, manufactured by Shimadzu Corporation) using a 1-point method using a mixed gas of 30% nitrogen and 70% helium as the adsorption gas. .

<Preparation of Li counter electrode battery>
The lithium composite oxide obtained in Examples and Comparative Examples, a conductive material (Denka black), and a binder (10 wt% PvdF/N-Methyl-2-Pyrrolidone solution) were mixed in a mixer (AR- 100 (manufactured by Thinky) to make the mixture uniform, thereby producing a positive electrode material ink. The obtained positive electrode material ink was applied to an aluminum foil to a thickness of 125 μm, dried at 80° C. for 30 minutes, dried under reduced pressure at 150° C. for more than 1 hour, and then cut into a circle with a diameter of 15.956 mm. The cut electrode was uniaxially pressed at 3 tons/cm ² and dried under reduced pressure at 150° C. for 2 hours to obtain a positive electrode.

The configuration of the battery other than the above positive electrode includes a solution containing LiPF6 at a concentration of 1.0M in a solution of EC and DMC mixed at a volume ratio of 1:2 as an electrolyte, and Celgard 2400 (diameter 19 mm, (manufactured by Celgard) was used.

As a negative electrode, lithium foil (diameter 16.16 mm, thickness 200 μm, manufactured by Honjo Metal Co., Ltd.) was used.
A CR2032 type coin cell was used as the cell.

<Preparation of C counter electrode battery>
As a negative electrode, a negative electrode ink was prepared by mixing spherulite graphite with a binder at a weight ratio of 90:10, then applied to copper foil, punched out to a diameter of 16.16 mmφ, and uniaxially pressed at 3 ton/cm ² . The weight of the negative electrode active material was adjusted by changing the coating thickness so that the negative electrode/positive electrode capacity ratio was 1.3.

The method of manufacturing the battery was the same as <Manufacture of Li counter electrode battery> except that the counter electrode was changed from lithium to carbon.

<Li counter electrode charge/discharge test>
The performance of the Li counter electrode battery was evaluated using a charge/discharge evaluation device (trade name: BTS2004W, manufactured by NAGANO) at 25° C. and measurements were performed in a voltage range of 2.0 V to 4.5 V (vs. lithium electrode). First, a charge/discharge test was performed at a current density of 0.03C for two cycles, and then an initial capacity evaluation was performed at a current density of 0.3C. The C rate was calculated as 0.3 C (66 mA/g), with the discharge capacity when charging and discharging at a current density of 0.03 C in a Li counter electrode cell being taken as the practical discharge capacity (220 mA/g).

<C counter electrode 25°C charge/discharge cycle test>
The performance of the C counter electrode battery was evaluated using a charge/discharge evaluation device (trade name: BTS2004W, manufactured by NAGANO) at 25° C. and measurements were performed in a voltage range of 2.0 V to 4.4 V (vs. carbon electrode). The charging termination condition was when the current value when 4.4V was maintained became 1/10 or less of the charging current value. First, a charge/discharge test was conducted for two cycles at a current density of 0.03C, and then a charge/discharge test was conducted for 100 cycles at a current density of 0.3C. The C rate was calculated as 0.3C (66mA/g), with the discharge capacity when charging and discharging at a current density of 0.03C being the practical discharge capacity (220mA/g).

Cycle stability was evaluated by capacity retention rate. The capacity retention rate was calculated as the ratio (B/A) of the discharge capacity (B) at the 100th cycle of 0.3C charging and discharging to the discharge capacity (A) at the 1st cycle of 0.3C charging and discharging.

<C counter electrode 45°C charge/discharge cycle test>
A charge/discharge cycle test was conducted at an evaluation temperature of 45°C. The first two cycles of charge/discharge test at 0.03C were performed at 25°C, and the cycle test evaluation was performed at 45°C for 50 cycles. The evaluation temperature, experimental conditions other than the number of cycles, and the method for calculating the capacity retention rate are the same as the C counter electrode 45° C. charge/discharge cycle test.

<Calculation of Mn precipitation amount>
After performing the cycle test, the carbon negative electrode taken out from the coin cell was washed with dimethyl carbonate, dissolved in 10 mL of a mixed solution of 5% sulfuric acid and 3% hydrogen peroxide, and then pure water was added to make a 100 mL aqueous solution. Analysis was performed using ICPAES (trade name: Optima 5300DV, manufactured by PerkinElmer).

The amount of Mn precipitated on the carbon negative electrode is determined by calculating the weight of Mn precipitated on the carbon electrode from the Mn concentration (A [ppm]) of the ICP measurement result, and calculating the amount of Mn precipitated on the carbon electrode as a ratio to the weight of Mn in the positive electrode active material (B [mg]). represent. B is not the weight of the active material, but only the weight of Mn calculated from the composition of the active material. At this time, the amount of Mn precipitation is expressed by the following formula.
Mn precipitation amount [wt%] = A/(10・B)

Example 1
The metal salt aqueous solution contains an aqueous solution containing 0.025 mol/L nickel sulfate (NiSO ₄ ), 0.025 mol/L titanyl sulfate (TiOSO ₄ ), and 1.95 mol/L manganese sulfate (MnSO ₄ ). there was. Note that the total concentration of all metals in the metal salt aqueous solution was 2.0 mol/L.

After putting 200 g of pure water into a 1.0 L reaction vessel, the temperature was raised to 60° C. and the mixture was stirred. The metal salt aqueous solution was added to the reaction vessel at a feed rate of 0.75 g/min. Furthermore, during the above supply operation, air was continued to be bubbled into the reaction vessel as an oxidizing agent at a supply rate of 1.0 L/min. Further, a 2.0 mol/L aqueous sodium hydroxide solution was intermittently added and mixed so that the pH of the mixed solution was 8.5. The precipitated slurry obtained by the reaction was filtered, washed, and dried at 120°C for 12 hours to obtain manganese oxide containing Mn, Ni and Ti (theoretical composition (Ni _0.025 Ti _0.025 Mn _0.95 ) ₃ O ₄ ) was obtained.

The manganese oxide obtained above was fired in air at 700° C. for 12 hours to produce a theoretical composition (Ni _0.025 Ti _0.025 Mn _0.95 ) ₂ O ₃ . Manganese oxide and commercially available lithium carbonate were dry mixed in a mortar for 20 minutes so that the Li/(Ni+Ti+Mn) molar ratio was 1.0 based on the weight ratio of the metal composition determined from ICP. The obtained mixed powder was placed in a baking dish, heated at 900°C for 12 hours in _N2 gas, and cooled to room temperature to form LiNi _0.025 Ti _0.025 Mn ₀ whose main phase has a zigzag layered structure. Obtained _{.95 O2} . The temperature increase rate and temperature decrease rate were 10° C./min.

Lithium phosphate Li ₃ PO ₄ was added to LiNi _0.025 Ti _0.025 Mn _0.95 O ₂ whose main phase had a zigzag layered structure, and mechanical milling was performed at 600 rpm for 36 hours in a closed container in an Ar atmosphere. A rock salt type Li _1.02 P _0.02 Ni _0.025 Ti _0.025 Mn _0.95 O ₂ was obtained. For mechanical milling, a zirconia container and balls are used, and three balls with a diameter of 10 mm are placed in 1.5 g of a lithium composite oxide sample, 0.037 g of lithium phosphate (equivalent to 2 mol% relative to the lithium composite oxide), and Ten 5 mm balls and 2 g of 1 mm diameter balls were used.

Next, the rock salt-type structure Li _1.02 P _0.02 Ni _0.025 Ti _0.025 Mn _0.95 O ₂ was heat-treated at 600°C for 12 hours in N ₂ gas to transform the zigzag layered structure into a matrix structure. A lithium composite oxide of Li _1.02 P _0.02 Ni _0.025 Ti _0.025 Mn _0.95 O _x having a domain with an α-NaFeO ₂ type layered structure was obtained.

Using the obtained lithium composite oxide, a lithium ion secondary battery was produced according to the above <Preparation of Li counter electrode battery> and <Preparation of C counter electrode battery>.

Example 2
The same method as in Example 1 except that lithium phosphate was not added to LiNi _0.025 Ti _0.025 Mn _0.95 O ₂ whose main phase had a zigzag layered structure obtained by the same method as in Example 1. Mechanical milling was performed to obtain rock salt type LiNi _0.025 Ti _0.025 Mn _0.95 O ₂ .

Next, the rock salt-type structure LiNi _0.025 Ti _0.025 Mn _0.95 O ₂ was heat-treated at 600 °C for 12 hours in Ar gas to create a zigzag layered structure as a matrix structure and an α-NaFeO _2- type layered structure. A lithium composite oxide of LiNi _0.025 Ti _0.025 Mn _0.95 O _x having the following domains was obtained.

Furthermore, lithium phosphate was added to a lithium composite oxide LiNi _0.025 Ti _0.025 Mn _0.95 O _x which had a zigzag layered structure as a mother structure and domains of an α-NaFeO ₂ type layered structure, and was processed using a ball mill. and mixed. Ball mill mixing was performed in an air atmosphere at 100 rpm for 12 hours. By heat-treating the mixture in N ₂ gas at 600°C for 12 hours, Li _1.02 P _0.02 Ni _0.025 Ti which has a zigzag layered structure as a matrix structure and a domain of α-NaFeO ₂ type layered structure A lithium composite oxide of _0.025 Mn _0.95 O _x was obtained.

Using the obtained lithium composite oxide, a lithium ion secondary battery was produced according to the above <Preparation of Li counter electrode battery> and <Preparation of C counter electrode battery>.

Example 3
The 0.037 g of lithium phosphate (equivalent to 2 mol% relative to the lithium composite oxide) used in mechanical milling was changed to 0.056 g of lithium phosphate (equivalent to 3 mol% relative to _the lithium composite oxide), and Li _1.03 P _0.03 having a zigzag layered structure as a parent structure and a domain of α-NaFeO ₂ type layered structure was prepared in the same manner as in Example 1 except that the heat treatment temperature was changed from 600°C to 700°C. A lithium composite oxide of Ni _0.025 Ti _0.025 Mn _0.95 O _x was obtained.

Using the obtained lithium composite oxide, a lithium ion secondary battery was produced according to the above <Preparation of Li counter electrode battery> and <Preparation of C counter electrode battery>.

Comparative example 1
Same as Example 1 except that lithium phosphate was not added to LiNi _0.025 Ti _0.025 Mn _0.95 O ₂ whose main phase had a zigzag layered structure obtained by the same method as Example 1. Mechanical milling was performed using the method described above to obtain rock salt type LiNi _0.025 Ti _0.025 Mn _0.95 O ₂ .

Next, the rock salt-type structure LiNi _0.025 Ti _0.025 Mn _0.95 O ₂ was heat-treated at 600 °C for 12 hours in Ar gas to create a zigzag layered structure as a matrix structure and an α-NaFeO _2- type layered structure. A lithium composite oxide of LiNi _0.025 Ti _0.025 Mn _0.95 O _x having the following domains was obtained.

Using the obtained lithium composite oxide, a lithium ion secondary battery was produced according to the above <Preparation of Li counter electrode battery> and <Preparation of C counter electrode battery>.

Comparative example 2
Same as Example 1 except that lithium phosphate was not added to LiNi _0.025 Ti _0.025 Mn _0.95 O ₂ whose main phase had a zigzag layered structure obtained by the same method as Example 1. Mechanical milling was performed using the method described above to obtain rock salt type LiNi _0.025 Ti _0.025 Mn _0.95 O ₂ .

Next, the rock salt-type structure LiNi _0.025 Ti _0.025 Mn _0.95 O ₂ was heat-treated at 700°C for 12 hours in Ar gas to form a zigzag layered structure as a matrix structure and an α-NaFeO _2- type layered structure. A lithium composite oxide of LiNi _0.025 Ti _0.025 Mn _0.95 O _x having the following domains was obtained.

Using the obtained lithium composite oxide, a lithium ion secondary battery was produced according to the above <Preparation of Li counter electrode battery> and <Preparation of C counter electrode battery>.

The 10 to 90° XRD patterns of the lithium composite oxides of Examples 1 to 3 and Comparative Examples 1 to 2 were confirmed, and the results are shown in FIG. The lithium composite oxide produced in the present invention has strong peaks on the rectangular (010), (011), (200), and (021) planes and weak peaks on the monoclinic (001) plane. I found out that it was. In addition, the lithium composite oxide produced in the present invention has a rectangular (010) plane shown at 15.3±1.0° (A) and a monoclinic plane shown at 18.2±1.0° (B). A peak of the crystal system (001) plane was confirmed. That is, it was found that the lithium composite oxide had a rectangular zigzag layered structure as a parent structure and domains of an α-NaFeO ₂ type layered structure. Furthermore, it was confirmed that the crystal structure of the lithium composite oxide produced by the present invention, which is composed of phosphorus composites, was not changed. Furthermore, the (A/B) peak integrated intensity ratio was calculated, and the results are shown in Table 1.

BET specific surface areas were measured for the lithium composite oxides of Examples 1 to 3 and Comparative Examples 1 to 2, and the results are shown in Table 1.
The initial capacity of the Li counter electrode was measured for the lithium composite oxides of Examples 1 to 3 and Comparative Examples 1 to 2 according to <Preparation of Li counter electrode battery> and <Li counter electrode charge/discharge test>, and the results are shown in Table 1. Ta.

When the BET specific surface area of Comparative Example 2 is 3.3 m ² /g, the initial capacity of the Li counter electrode is small and high capacity is not developed. Therefore, the BET specific surface area is required to be 3.5 m ² /g or more.

The initial capacity of the C counter electrode at 25°C was measured for the lithium composite oxides produced in Examples 1 to 2 and Comparative Example 1 according to <Preparation of C counter electrode battery> and <C counter electrode charge/discharge test at 25°C>, and the capacity retention rate was determined. The results of the calculation are shown in Table 2. Table 2 shows the amount of Mn precipitation calculated according to <Measurement of Mn precipitation amount> using the carbon negative electrode taken out from the battery after the cycle test.

From the results of the 0.3C cycle stability test shown in Table 2, Examples 1 and 2 showed improved charge-discharge cycle stability compared to Comparative Example 1, which was produced without phosphorus compounding.

The amount of Mn precipitation taken out and measured from the batteries manufactured in Examples 1 and 2 shown in Table 2 was also lower than Comparative Example 1, indicating that Mn elution from the positive electrode was suppressed. We have achieved a lithium-ion secondary battery with high capacity, high output, and high cycle stability.

For the lithium composite oxides produced in Example 3 and Comparative Examples 1 and 2, the initial capacity of the C counter electrode at 45°C was measured according to <Preparation of C counter electrode battery> and <C counter electrode charge/discharge test at 45°C>, and the capacity retention rate was determined. The results of the calculation are shown in Table 3. Table 3 shows the amount of Mn precipitation calculated according to <Measurement of Mn precipitation amount> using the carbon negative electrode taken out from the battery after the cycle test.

From the results of the 0.3C cycle stability test shown in Table 3, Example 3 showed improved charge-discharge cycle stability compared to Comparative Examples 1 and 2, which were manufactured without phosphorus compounding.

The amount of Mn precipitation taken out and measured from the battery manufactured in Example 3 shown in Table 3 was also lower than Comparative Examples 1 and 2, indicating that Mn elution from the positive electrode was suppressed. We have achieved a lithium-ion secondary battery with high capacity, high output, and high cycle stability.

The lithium composite oxide of the present invention is expected to be used in the field of positive electrode active materials for lithium ion secondary batteries as a positive electrode active material that is inexpensive, has high capacity, high output, and has high cycle stability.

Claims (10)

It is represented by the compositional formula Li _x P _y Me _z Mn _1-z O ₂ (0<x≦1.3, 0<y≦0.1, 0<z≦0.2), and Me is Al , Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, Zn, and Zr, and has a rectangular zigzag layered structure. The integrated intensity of the diffraction peak observed at 15.3 ± 1.0° in powder X-ray diffraction (A), which has a monoclinic or rhombohedral α-NaFeO ₂ type layered structure domain, has a parent structure of and the diffraction peak integrated intensity (B) observed at 18.2±1.0°, the intensity ratio (A/B) is 0.5 or more, and the BET specific surface area is 3.5 to 15 m ² /g. A certain lithium composite oxide. After assembling a carbon counter electrode cell and performing a 100 cycle charge/discharge test at 25°C, 2.0-4.4V (vs. carbon electrode), and current density of 66 mA/g, the carbon negative electrode was taken out, dissolved in acid, and subjected to ICP method. The lithium composite oxide according to claim 1, wherein the amount of Mn precipitated when measured is 1.0 wt% or less based on the weight of Mn in the positive electrode active material. Composition formula (Me _y Mn _1-y ) _a O _b (However, 1.3<a/b<1.6, 0<y≦0.2, and Me is Al, Co, Cr, Cu, one or more metals selected from the group consisting of Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, Zn, and Zr), and the average oxidation number of the metal ions is 2.6 or more and 3 A lithium composite oxide whose main phase has a zigzag layered structure and is represented by Li _x Me _y Mn _1-y O ₂ is synthesized by mixing and sintering a manganese compound and a lithium compound that are less than .3. The method for producing a lithium composite oxide according to claim 1 or 2, wherein lithium phosphate is added to the Li _x Me _y Mn _1-y O _{2 ,} which is subjected to mechanical milling, and then heat treated in an inert gas. Composition formula (Me _y Mn _1-y ) _a O _b (However, 1.3<a/b<1.6, 0<y≦0.2, and Me is Al, Co, Cr, Cu, one or more metals selected from the group consisting of Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, Zn, and Zr), and the average oxidation number of the metal ions is 2.6 or more and 3 A lithium composite oxide whose main phase has a zigzag layered structure and is represented by Li _x Me _y Mn _1-y O ₂ is synthesized by mixing and sintering a manganese compound and a lithium compound that are less than .3. Li _x Me _y Mn _1-y O ₂ is mechanically milled, then heat treated in an inert gas, lithium phosphate is added and mixed, and then heat treated again in an inert gas. Item 2. The method for producing a lithium composite oxide according to item 2. The metal composition is Me _y Mn _1-y (however, 0<y≦0.2, and Me is Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, Li _x Me _y Mn _1-y O obtained by hydrothermally treating a mixture of a manganese compound (one or more metals selected from the group consisting of Zn and Zr) and a lithium compound in an alkaline aqueous solution. _3. The method for producing a lithium composite oxide according to claim 1, wherein lithium phosphate is added to and mixed with the lithium composite oxide represented by 2, and then heat treated in an inert gas. The metal composition is Me _y Mn _1-y (however, 0<y≦0.2, and Me is Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, A manganese compound (which is one or more metals selected from the group consisting of Zn and Zr), a lithium compound, and phosphoric acid are hydrothermally treated in an alkaline aqueous solution, and then heat-treated in an inert gas. The method for producing a lithium composite oxide according to claim 2. The metal composition is Me _y Mn _1-y (however, 0<y≦0.2, and Me is Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, Li _x Me _y Mn _1- obtained by mixing a manganese compound Me _y Mn _1-y OOH (which is one or more metals selected from the group consisting of Zn and Zr) with lithium hydroxide and firing it. The method for producing a lithium composite oxide according to claim 1 or _{2 ,} wherein lithium phosphate is added to and mixed with the lithium composite oxide represented by yO2, and then heat-treated in an inert gas. The metal composition is Me _y Mn _1-y (however, 0<y≦0.2, and Me is Al, Co, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Si, Ti, V, W, One or more metals selected from the group consisting of Zn and Zr), a manganese compound Me _y Mn _1-y OOH, lithium phosphate, and lithium hydroxide are mixed, fired, and then heated in an inert gas. The method for producing a lithium composite oxide according to claim 1 or 2, wherein the lithium composite oxide is heat-treated. An electrode comprising the lithium composite oxide according to claim 1 or 2. A lithium ion secondary battery using the electrode according to claim 9 as a positive electrode.

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