JP7193315B2 - Lithium-manganese composite oxide, lithium secondary battery, and method for producing lithium-manganese composite oxide - Google Patents

Description

The present specification discloses a lithium-manganese composite oxide, a lithium secondary battery, and a method for producing a lithium-manganese composite oxide.

In general, materials that belong to the space group Fm-3m (rock salt type structure) when subjected to X-ray diffraction measurement cannot be used as positive electrode materials because they do not have paths for lithium ions in the crystal structure. It's here. However, in recent years, a positive electrode material containing excessive lithium, for example, by setting the ratio of the molar amount (MLi) of lithium ions to the molar amount (MTM) of transition metal ions to MLi/MTM > 1.0, rock salt type First-principles calculations have shown that lithium ions move within the crystal structure (see, for example, Non-Patent Document 1).

As a composite oxide having such a rock salt structure, for example, a lithium molybdenum composite oxide having a rock salt structure has been proposed (see, for example, Patent Document 1). It is said that this composite oxide has a good discharge capacity and a good discharge capacity maintenance rate because it has a rock salt structure, which is a metastable phase. A lithium secondary battery containing a lithium molybdenum iron composite oxide having a rock salt structure as an active material has also been proposed (see, for example, Patent Document 2). This composite oxide is said to be capable of increasing the capacity of lithium-ion batteries. Further, as the composite oxide, a case where Li _1.3 Nb _0.3 Me _0.4 O ₂ (Me is Fe, Mn and V) and Li _1.2 Ti _0.4 Mn _0.4 O ₂ having a rock salt structure is proposed for the electrode. (For example, see Non-Patent Document 1, etc.).

JP 2017-202954 A JP-A-2017-33928

Advanced Energy Materials, 4, 1400478 (2014) Nature Communications, 7, 13814 (2016)

By the way, in the above-mentioned literature, the use of a composite oxide having a rock salt structure as an active material for a lithium secondary battery is being studied, and it is said that the discharge capacity and the capacity retention rate are good, but it is still It was not sufficient, and further improvement was desired. That is, a novel composite oxide has been desired that can further increase the discharge capacity and durability.

The present disclosure has been made in view of such problems, and provides a lithium manganese composite oxide, a lithium secondary battery, and a method for producing a lithium manganese composite oxide that can further increase discharge capacity and durability. The main purpose is

As a result of intensive research to achieve the above-described object, the present inventors have found that a lithium-manganese composite oxide having a rock salt structure and a spinel structure in a predetermined range has excellent discharge capacity and durability. can be further enhanced, and have completed the invention disclosed in this specification.

That is, the lithium-manganese composite oxide disclosed in the present specification is
A lithium manganese composite oxide used as an electrode active material for a lithium secondary battery,
It includes a rock salt type structure and a spinel type structure, and the spinel type structure is contained in the range of 5% by mass or more and 35% by mass or less.

The lithium secondary battery disclosed herein is
a positive electrode having the lithium-manganese composite oxide described above as a positive electrode active material;
a negative electrode having a negative electrode active material;
an ion conducting medium interposed between the positive electrode and the negative electrode and conducting lithium ions;
is provided.

The method for producing a lithium-manganese composite oxide disclosed herein comprises
A method for producing a lithium-manganese composite oxide used as an electrode active material for a lithium secondary battery, comprising:
A molar ratio M2/ between the number of moles M2 of basic composition formula Li ₂ MnO ₃ and the number of moles M1 of basic composition formula LiMnO ₂ obtained by firing in the range of 800° C. to 1100° C. and 6 hours to 15 hours. Raw materials are blended so that M1 is in the range of more than 10/90 and less than 60/40, and mixed and pulverized in the range of 20 hours or more and 40 hours or less to obtain the spinel structure including the rock salt structure and the spinel structure. is adjusted to be contained in the range of 5% by mass or more and 35% by mass or less,
includes.

The present disclosure can provide a lithium-manganese composite oxide, a lithium secondary battery, and a method for producing a lithium-manganese composite oxide that can further increase discharge capacity and durability. The reason why such an effect is obtained is presumed as follows. In general, the molar amount of lithium ions contained in the positive electrode material is the maximum capacity of the battery. Taking in and out is important for increasing the capacity of the positive electrode material. Exhibiting an X-ray diffraction peak in the space group Fm-3m (rock salt type), oxides composed of excess lithium are known to exhibit oxidation-reduction reactions of not only transition metal ions but also oxygen. It is still unclear, and it has not been possible to stably charge and discharge. In the present disclosure, it is presumed that by combining the spinel structure, the positive electrode material attributed to the rock salt structure can stably charge and discharge while maintaining a high capacity. The reason for this is, for example, that the spinel type structure tends to have an oxygen defect composition more than the rock salt type structure, and it is considered that this stabilizes the oxidation-reduction reaction of oxygen. When the spinel type structure is 5% by mass or more, a sufficient composite effect can be obtained, and when it is 35% by mass or less, the proportion of the active rock salt type structure can be secured, and the discharge capacity is further increased. It is speculated that Here, the content of the spinel structure is determined by the Rietveld analysis of the two-component structural model of the space groups Fm-3m (rock salt structure) and Fd-3m (spinel structure) based on the X-ray diffraction measurement results. shall be calculated by performing

FIG. 2 is a schematic diagram showing an example of the configuration of a lithium secondary battery 20; 2 shows the result of X-ray diffraction measurement of the composite oxide of Experimental Example 1. FIG. Fig. 2 shows charge-discharge curves of a cell using the composite oxide of Experimental Example 1 as an electrode.

(lithium manganese composite oxide)
The lithium-manganese composite oxide of the present disclosure is used as an electrode active material for lithium secondary batteries. This lithium-manganese composite oxide includes a rock salt structure and a spinel structure, and contains the spinel structure in a range of 5% by mass or more and 35% by mass or less. By containing the spinel structure within this range, the composite oxide attributed to the rock salt structure can stably charge and discharge while maintaining a high capacity. The lithium-manganese composite oxide preferably contains a spinel structure in an amount of 25% by mass or less, more preferably 20% by mass or less. In addition, the lithium-manganese composite oxide preferably contains a spinel structure in an amount of 10% by mass or more, more preferably 12% by mass or more. Here, the content of the spinel structure is determined by the Rietveld analysis of the two-component structural model of the space groups Fm-3m (rock salt structure) and Fd-3m (spinel structure) based on the X-ray diffraction measurement results. shall be calculated by

In the lithium-manganese composite oxide of the present disclosure, the molar ratio M2/M1 between the number of moles M2 of the basic composition formula Li ₂ MnO ₃ and the number of moles M1 of the basic composition formula LiMnO ₂ is in the range of more than 10/90 and less than 60/40. is preferably When M2/M1 is within this range, the discharge capacity can be further improved. The molar ratio M2/M1 is preferably 20/80 or more, and may be 30/70 or more. Also, the molar ratio M2/M1 is preferably in the range of 50/50 or less, and may be in the range of 45/55 or less.

Similarly, the lithium-manganese composite oxide is represented by the basic composition formula Li _(2+2x)/(2+x) Mn _{(2/(2+x))- y My} O ₂ , .1<x<0.6 is preferred. When x is within this range, the discharge capacity can be further improved. Also, x is preferably 0.2 or more, and may be 0.3 or more. Furthermore, x is preferably 0.5 or less, and may be 0.45 or less. In the basic composition formula, M may be one or more of Ti, Al and Fe. By replacing M with Mn, the capacity retention rate can be further increased. Of these, M is preferably Ti. This M preferably satisfies 0≦y≦0.2 in the above basic composition formula. When y is within this range, the discharge capacity can be further improved. More preferably, M satisfies y≦0.1.

(Method for producing lithium-manganese composite oxide)
The production method of the present disclosure is a method for producing the aforementioned lithium-manganese composite oxide used as an electrode active material for lithium secondary batteries. This manufacturing method may include, for example, an adjustment step of adjusting the structure of the composite oxide. Also, this adjustment process is It may include the raw material preparation process and the mixed pulverization process. In this production method, when a plurality of types of lithium manganese oxides having a layered structure are mixed and pulverized to transition to a rock salt structure, the spinel is produced by appropriately adjusting the sintering temperature, sintering time, and mixing and pulverizing time of the raw materials. A treatment may be performed to allow the mold structure to remain in the rock salt structure within a predetermined content range. In this adjustment step, the lithium-manganese composite oxide is adjusted so that the spinel structure is included in the range of 5 mass % or more and 35 mass % or less, including the rock salt structure and the spinel structure. In this production method, the range described for the above lithium-manganese composite oxide, such as the content of the spinel structure and the compounding ratio of the raw materials, can be appropriately employed.

In the raw material production process, multiple kinds of lithium manganese oxides are produced while adjusting the firing conditions. In this treatment, Li ₂ MnO ₃ and LiMnO ₂ are produced as the raw material lithium manganese oxide. In this treatment, the raw material Li ₂ MnO ₃ is obtained by firing at a temperature of 800° C. to 1100° C. for 6 hours to 15 hours. The spinel structure contained in the lithium-manganese composite oxide can be adjusted according to the strength of the layered structure of Li ₂ MnO ₃ . Li ₂ MnO ₃ can be produced, for example, using lithium hydroxide and manganese dioxide as raw materials. LiMnO ₂ is prepared by mixing Li ₂ MnO ₃ and MnO in equimolar amounts, and firing in an inert atmosphere (for example, in Ar) at a temperature of 900° C. or higher and 1100° C. or lower for 6 hours or more and 24 hours or less. can be obtained by

In the mixed pulverization treatment, the lithium manganese oxide prepared above is blended at a predetermined ratio, and mixed and pulverized while adjusting the pulverization conditions. In this treatment, the raw materials are blended so that the molar ratio M2/M1 between the number of moles M2 of Li ₂ MnO ₃ and the number of moles M1 of LiMnO ₂ is in the range of more than 10/90 and less than 60/40. In the mixed pulverization process, the basic composition formula Li _(2+2x)/(2+x) Mn _{(2/(2+x))- y My} O ₂ (where 0.2<x<0.6, M is one or more of Ti, Al and Fe, and the raw materials may be blended so that 0≤y≤0.2). Further, in this treatment, mixing and pulverization may be performed for 20 hours or more and 40 hours or less. Mixing pulverization can be performed by, for example, a ball mill or a planetary ball mill, and is preferably performed by a planetary ball mill. In the planetary ball mill, the number of revolutions may be appropriately set according to the volume of the raw material. A range is more preferred. By performing such an adjustment process, the lithium-manganese composite oxide described above can be produced.

(lithium secondary battery)
A lithium secondary battery of the present disclosure includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an ion conducting medium interposed between the positive electrode and the negative electrode to conduct lithium ions. This lithium secondary battery has the aforementioned lithium-manganese composite oxide as a positive electrode active material.

The positive electrode is prepared by mixing a positive electrode active material, a conductive material, and a binder, adding an appropriate solvent to make a paste-like positive electrode mixture, applying and drying it on the surface of a current collector, and optionally It may be formed by compression to increase its density. The conductive material contained in the positive electrode is not particularly limited as long as it is an electronically conductive material that does not adversely affect the battery performance of the positive electrode. , carbon black, ketjen black, carbon whisker, needle coke, carbon fiber, metals (copper, nickel, aluminum, silver, gold, etc.), or a mixture of two or more thereof can be used. Among these, carbon black and acetylene black are preferable as the conductive material from the viewpoint of electronic conductivity and coatability. The binder contained in the positive electrode plays a role of binding the active material particles and the conductive material particles. Alternatively, thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR) and the like can be used singly or as a mixture of two or more. Cellulose-based or styrene-butadiene rubber (SBR) aqueous dispersions, which are water-based binders, can also be used. Examples of solvents for dispersing the positive electrode active material, conductive material, and binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methylethylketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, and N,N-dimethylaminopropylamine. , ethylene oxide, and tetrahydrofuran can be used. Alternatively, a dispersant, a thickener, or the like may be added to water, and the active material may be slurried with a latex such as SBR. As the thickening agent, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used singly or as a mixture of two or more. Application methods include, for example, roller coating such as applicator roll, screen coating, doctor blade method, spin coating, and bar coater, and any thickness and shape can be obtained using any of these methods. Current collectors include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, and conductive glass. The surface of which is treated with carbon, nickel, titanium, silver, or the like can be used. For these, it is also possible to oxidize the surface. Examples of the shape of the current collector include foil, film, sheet, net, punched or expanded, lath, porous, foam, and fiber group formations. The current collector used has a thickness of, for example, 1 to 500 μm.

The negative electrode may be formed by adhering the negative electrode active material and the current collector. A negative electrode material having a shape may be coated on the surface of a current collector, dried, and optionally compressed to increase the electrode density. Examples of negative electrode active materials include inorganic compounds such as lithium, lithium alloys and tin compounds, carbonaceous materials capable of intercalating and deintercalating lithium ions, composite oxides containing multiple elements, and conductive polymers. Examples of carbonaceous materials include cokes, vitreous carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Among them, graphites such as artificial graphite and natural graphite have an operating potential close to that of metallic lithium, can be charged and discharged at a high operating voltage, and suppress self-discharge when lithium salt is used as a supporting salt. Moreover, the irreversible capacity during charging can be reduced, which is preferable. Examples of composite oxides include lithium-titanium composite oxides and lithium-vanadium composite oxides. Among them, carbonaceous materials are preferable as the negative electrode active material from the viewpoint of safety. As the conductive material, binder, solvent, and the like used for the negative electrode, those exemplified for the positive electrode can be used. The current collector of the negative electrode includes copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc. For that purpose, for example, copper or the like whose surface is treated with carbon, nickel, titanium, silver, or the like can also be used. For these, it is also possible to oxidize the surface. A current collector having the same shape as that of the positive electrode can be used.

The ion-conducting medium may be a non-aqueous electrolytic solution containing a lithium-containing supporting salt and a non-aqueous solvent. Examples of the solvent for the non-aqueous electrolytic solution include carbonates, esters, ethers, nitriles, furans, sulfolanes, dioxolanes, and the like, and these can be used singly or in combination. Specifically, the carbonates include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t -chain carbonates such as butyl carbonate, di-i-propyl carbonate and t-butyl-i-propyl carbonate, cyclic esters such as γ-butyl lactone and γ-valerolactone, methyl formate, methyl acetate, ethyl acetate, Chain esters such as methyl butyrate; ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane; nitriles such as acetonitrile and benzonitrile; furans such as tetrahydrofuran and methyltetrahydrofuran; Dioxolanes such as sulfolanes, 1,3-dioxolane, methyldioxolane, and the like are included. Among these, a combination of cyclic carbonates and chain carbonates is preferred.

The supporting salt is, for example, _LiPF6 , _LiBF4 , _LiAsF6 , _LiCF3SO3 , LiN( _CF3SO2 ) ₂ , _{LiC ( CF3SO2} ) ₃ , _LiSbF6 , _LiSiF6 , _LiAlF4 , _LiSCN , LiClO ₄ , LiCl, LiF, LiBr, LiI, _LiAlCl4 and the like. Among them, from the group consisting of inorganic salts such as _LiPF6 , _LiBF4 , _LiAsF6 and LiClO4, and organic salts such as _{LiCF3SO3 ,} LiN _{( CF3SO2} ) ₂ and _{LiC ( CF3SO2} ) ₃ From the viewpoint of electrical properties, it is preferable to use one selected salt or a combination of two or more selected salts. The concentration of the supporting salt in the non-aqueous electrolytic solution is preferably 0.1 mol/L or more and 5 mol/L or less, more preferably 0.5 mol/L or more and 2 mol/L or less. When the supporting electrolyte is dissolved in a concentration of 0.1 mol/L or more, a sufficient current density can be obtained, and when it is 5 mol/L or less, the electrolytic solution can be made more stable.

The lithium secondary battery of the present disclosure may have a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the lithium secondary battery. Porous membranes are mentioned. These may be used alone, or may be used in combination.

The shape of the lithium secondary battery of the present disclosure is not particularly limited, and examples include coin-shaped, button-shaped, sheet-shaped, laminated-type, cylindrical-shaped, flat-shaped, and square-shaped. Also, a plurality of such lithium secondary batteries may be connected in series and applied to a large-sized battery used in an electric vehicle or the like. FIG. 1 is a schematic diagram showing an example of a lithium secondary battery 20 of this embodiment. This lithium secondary battery 20 includes a positive electrode sheet 23 having a positive electrode mixture 22 formed on a current collector 21, a negative electrode sheet 26 having a negative electrode mixture 25 formed on the surface of the current collector 24, a positive electrode sheet 23 and a negative electrode sheet. 26, and a non-aqueous electrolytic solution 29 filling between the positive electrode sheet 23 and the negative electrode sheet 26. In this lithium secondary battery 20, a separator 28 is sandwiched between a positive electrode sheet 23 and a negative electrode sheet 26, which are wound and inserted into a cylindrical case 32. A positive electrode terminal 34 and a negative electrode sheet 26 connected to the positive electrode sheet 23 are connected to and a negative electrode terminal 36 connected to . The positive electrode mixture 22 contains, as a positive electrode active material, a lithium-manganese composite oxide having a rock-salt structure and containing a spinel structure in a range of 5% by mass to 35% by mass.

The lithium-manganese composite oxide, the method for producing the same, and the lithium secondary battery according to the present embodiment, which have been described in detail above, can further increase the discharge capacity and durability. The reason why such an effect is obtained is that, for example, by combining the spinel structure, the positive electrode material attributed to the rock salt structure can stably charge and discharge while maintaining a high capacity. It is speculated that The spinel type structure has a property of being more likely to have an oxygen defect composition than the rock salt type structure, and it is considered that this stabilizes the oxidation-reduction reaction of oxygen. When the spinel type structure is 5% by mass or more, a sufficient composite effect can be obtained, and when it is 35% by mass or less, the proportion of the active rock salt type structure can be secured, and the discharge capacity is further increased. It is speculated that

It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present disclosure.

Experimental examples will be described below in which the lithium-manganese composite oxide and the lithium secondary battery of the present disclosure were specifically produced. Note that Experimental Examples 3 to 8 correspond to Comparative Examples, and Experimental Examples 1, 2, and 9 to 13 correspond to Examples.

(Preparation of synthetic raw materials)
Li ₂ MnO ₃ was synthesized by mixing lithium hydroxide and manganese dioxide in a molar ratio of 2:1 and calcining the mixture at 1000° C. for 12 hours in argon. LiMnO ₂ was synthesized by mixing the obtained Li ₂ MnO ₃ and MnO at a molar ratio of 1:1 and firing the mixture in argon at 1000° C. for 12 hours.

(Experimental example 1)
Li ₂ MnO ₃ and LiMnO ₂ prepared by the above method are used, and the molar ratio M2/M1 between the number of moles M2 of Li ₂ MnO ₃ and the number of moles M1 of LiMnO ₂ is adjusted to 30/70, and These oxides were weighed so that the total mass was 20 g. This weighed material was put into a zirconia pot with an internal volume of 500 mL containing 500 g of zirconia balls with a diameter of 10 mm. This pot was set in a planetary ball mill (pulverisette 6 manufactured by FRITSCH), and the treatment was performed for 30 hours at a revolution speed of 500 rpm. Thus, _{Li1.13Mn0.87O2} (Li( _{2 +2x)/(2+x)} Mn[2/( _{2 +x)]- yMyO2} , _x =0.3, y=0) was prepared. The resulting product was used as the lithium-manganese composite oxide of Experimental Example 1.

(Experimental example 2)
In Experimental Example 1, Li ₂ MnO ₃ was synthesized by firing at 900° C. for 12 hours, and treated in a planetary ball mill at a revolution speed of 600 rpm for 25 hours to obtain Li _1.13 Mn _0.87 O ₂ (Li _{(2+2x) /(2+x)} Mn _{[2/(2+x)]-yM y} O ₂ (x=0.3, y=0) was prepared.

(Experimental example 3)
In Experimental Example 1, Li ₂ MnO ₃ was synthesized by firing at 850° C. for 8 hours, and treated in a planetary ball mill at a revolution speed of 600 rpm for 50 hours to obtain Li _1.13 Mn _0.87 O ₂ (Li _{(2+2x) /(2+x)} Mn _{[2/(2+x)]-yM y} O ₂ (x=0.3, y=0) was prepared.

(Experimental example 4)
In Experimental Example 1, Li ₂ MnO ₃ was synthesized by firing at 1000° C. for 12 hours, and treated in a planetary ball mill at a revolution speed of 500 rpm for 15 hours to obtain Li _1.13 Mn _0.87 O ₂ (Li _{(2+2x) /(2+x)} Mn _{[2/(2+x)]-yM y} O ₂ (x=0.3, y=0) was prepared.

(Experimental example 5)
Li ₂ MnO ₃ was synthesized and subjected to planetary ball mill treatment under the same conditions as in Experimental Example 3 to produce Li _1.09 Mn _0.91 O ₂ (Li _(2+2x)/(2+x) Mn _[2/(2+x)] xx=0.2, y=0 when expressed as _{-yM y} O ₂ ).

(Experimental example 6)
Synthesis of Li ₂ MnO ₃ and treatment with a planetary ball mill were carried out under the same conditions as in Experimental Example 3 to produce Li _1.20 Mn _0.80 O ₂ (Li _(2+2x)/(2+x) Mn _{[2/(2+x)] -yM y} O ₂ (x=0.5, y=0) was prepared.

(Experimental example 7)
Li ₂ MnO ₃ was synthesized and subjected to planetary ball mill treatment under the same conditions as in Experimental Example 3 to obtain Li _1.05 Mn _0.95 O ₂ (Li _(2+2x)/(2+x) Mn _{[2/(2+x)] -yM y} O ₂ (x=0.1, y=0) was prepared.

(Experimental example 8)
Synthesis of Li ₂ MnO ₃ and treatment with a planetary ball mill were carried out under the same conditions as in Experimental Example 3 to obtain Li _1.23 Mn _0.77 O ₂ (Li _(2+2x)/(2+x) Mn _{[2/(2+x)] -yM y} O ₂ (x=0.6, y=0) was prepared.

(Experimental example 9)
Synthesis of Li ₂ MnO ₃ and treatment with a planetary ball mill were carried out under the same conditions as in Experimental Example 1 to produce Li _1.09 Mn _0.91 O ₂ (Li _(2+2x)/(2+x) Mn _{[2/(2+x)] -yM y} O ₂ (x=0.2, y=0) was prepared.

(Experimental example 10)
Li ₂ MnO ₃ was synthesized and subjected to planetary ball mill treatment under the same conditions as in Experimental Example 1 to produce Li _1.20 Mn _0.80 O ₂ (Li _(2+2x)/(2+x) Mn _{[2/(2+x)] -yM y} O ₂ (x=0.5, y=0) was prepared.

(Experimental example 11)
Li ₂ MnO ₃ was synthesized under the same conditions as in Experimental Example 1. Li ₂ TiO ₃ was synthesized by mixing lithium hydroxide and titanium dioxide in a molar ratio of 2:1 and firing the mixture at 1000° C. for 12 hours in argon. Li ₂ MnO ₃ , LiMnO ₂ and Li ₂ TiO ₃ were used, and the molar ratio of Li ₂ MnO ₃ , LiMnO ₂ and Li ₂ TiO ₃ was adjusted to 20/70/10. It was weighed so that the mass was 20 g. _{Li1.13Mn0.78Ti0.09O2} ( _Li ( _{2 +2x)/(2+x) Mn [2/(2+x)]- y My} M=Ti, x=0.3, y=0.09 when expressed in terms of O ₂ ).

(Experimental example 12)
LiAlO ₂ was synthesized by mixing lithium hydroxide and aluminum hydroxide at a molar ratio of 1:1 and calcining the mixture at 750° C. in air for 12 hours. Li ₂ MnO ₃ , LiMnO ₂ and LiAlO ₂ were used, and the molar ratio of Li ₂ MnO ₃ , LiMnO ₂ and LiAlO ₂ was adjusted to 30/60/10, and the total mass of these oxides was 20 g. Weighed to be _{Li1.13Mn0.78Al0.09O2} ( _Li ( _{2 +2x)/(2+x) Mn [2/(2+x)]- y My} M=Al, x=0.3, y=0.09 when expressed in terms of O ₂ ).

(Experimental example 13)
LiFeO ₂ was synthesized by mixing lithium hydroxide and iron oxyhydroxide in a molar ratio of 1:1 and calcining the mixture at 750° C. in air for 12 hours. Li ₂ MnO ₃ , LiMnO ₂ and LiFeO ₂ were used and the molar ratio of Li ₂ MnO ₃ , LiMnO ₂ and LiFeO ₂ was adjusted to 30/60/10, and the total mass of these oxides was 20 g. Weighed to be _{Li1.13Mn0.78Fe0.09O2} ( _Li ( _{2 +2x)/(2+x) Mn [2/(2+x)]- y My} M=Fe, x=0.3, y=0.09 when expressed as O ₂ ).

(X-ray diffraction measurement)
A powder X-ray diffraction measurement was performed on the sample. The measurement was carried out using an X-ray diffractometer (Ultima IV manufactured by Rigaku Co., Ltd.) using CuKα rays (wavelength: 1.54051 Å) as radiation. Measurement was performed by setting the applied voltage to 50 kV and the current to 40 mA. Further, the measurements were recorded at a scanning speed of 5°/min in the angle range of 2θ from 10° to 100°. 2 is the result of X-ray diffraction measurement of the lithium-manganese composite oxide of Experimental Example 1. FIG. As shown in FIG. 2, in Experimental Example 1, it was found that the space groups Fm-3m (rock salt type structure) and Fd-3m (spinel type structure) are included. Based on the measurement results, Rietveld analysis was performed on a two-component structural model of a rock salt structure and a spinel structure using GSAS software, and the ratio of the rock salt structure and the spinel structure was calculated. As a result, the ratio of the spinel structure was 12% by mass. Similarly, for Experimental Examples 2 to 13, the content of the spinel phase was calculated for those containing the spinel phase.

(Preparation of bipolar evaluation cell)
The obtained sample was used as the positive electrode active material, and the mixture ratio was 85% by mass of the active material, 10% by mass of carbon black as the conductive material, and 5% by mass of polyvinylidene fluoride as the binder. An appropriate amount of N-methyl-2-pyrrolidone was added as a dispersing agent and dispersed to obtain a slurry mixture. This slurry mixture was uniformly applied to an aluminum foil current collector having a thickness of 15 μm and dried by heating to prepare a coated sheet. The coated sheet was then passed through a roll press to densify it. A disk-shaped electrode was prepared by punching out the positive electrode produced by the above method to have an area of 2.05 cm ² . A bipolar evaluation cell was prepared by sandwiching a polyethylene separator impregnated with a non-aqueous electrolytic solution between the electrodes as a working electrode and a lithium metal foil (thickness: 300 μm) as a counter electrode. For the non-aqueous electrolyte, _LiPF6 was dissolved at a concentration of 1 M in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio of 30/40/30. I used something else.

(Charging and discharging test)
Using the bipolar evaluation cell, a charge/discharge test was conducted in a temperature environment of 20° C. at a rate of 0.05 C and in a range of 5.0 V to 1.0 V. 3 is an initial charge/discharge curve of a bipolar evaluation cell using the lithium-manganese composite oxide of Experimental Example 1. FIG. The initial discharge capacity Qi was 258 mAh/g. This charge/discharge cycle was repeated 5 times, and the capacity retention rate was calculated by the formula Qc/Qi×100 with respect to the discharge capacity Qc after 5 cycles.

(Results and discussion)
Table 1 summarizes the compositions, spinel phase contents (% by mass), discharge capacities (mAh/g), and capacity retention rates (%) of Experimental Examples 1 to 13. As shown in Experimental Examples 1 to 4 in Table 1, in the sample with x = 0.3, the X-ray diffraction peak attributable to Fd-3m (spinel type) is the X of the space group Fm-3m (rock salt type). It was found that the capacity retention rate is improved when the abundance ratio is in the range of 5% by mass or more and 35% by mass or less, more preferably in the range of 10% by mass or more and 20% by mass or less with respect to the line diffraction peak. Further, as shown in Experimental Examples 3 and 5 to 8, in the basic composition formula Li _(2+2x)/(2+x) Mn _{[2/(2+x)]- y My} O ₂ , 0.1 It was found that the discharge capacity increased in the range of <x<0.6, more preferably in the range of 0.2≦x≦0.5. That is, the molar ratio M2/M1 between the number of moles M2 of the basic composition formula Li ₂ MnO ₃ and the number of moles M1 of the basic composition formula LiMnO ₂ is in the range of more than 10/90 and less than 60/40, more preferably 20/80 or more. It was found that the discharge capacity increased in the range of 50/50 or less. Furthermore, as shown in Experimental Examples 5, 6, 9, and 10, even in the samples with x = 0.2 and 0.5, the effect of improving the capacity retention rate by compositing the spinel structure was observed. Do you get it. Further, as shown in Experimental Examples 11 to 13, it was found that the capacity retention rate was further improved by further compounding at least one of M=Ti, Al, and Fe. It is presumed that the above effect can be obtained in the range of 0≦y≦0.2, more preferably in the range of y≦0.1, in the above basic composition formula.

It goes without saying that the present disclosure is by no means limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure.

INDUSTRIAL APPLICABILITY The lithium-manganese composite oxide, the lithium secondary battery, and the method for producing the lithium-manganese composite oxide disclosed in the present specification can be used in the technical field of secondary batteries.

20 Lithium secondary battery 21 Current collector 22 Positive electrode mixture 23 Positive electrode sheet 24 Current collector 25 Negative electrode mixture 26 Negative electrode sheet 28 Separator 29 Non-aqueous electrolytic solution 32 Cylindrical case 34 Positive electrode terminal , 36 negative terminal.

Claims (7)

A lithium manganese composite oxide used as an electrode active material for a lithium secondary battery,
A lithium-manganese composite comprising a rock salt structure that can be assigned to space group Fm-3m and a spinel structure that can be assigned to space group Fd-3m, wherein the spinel structure is contained in a range of 5% by mass or more and 35% by mass or less. oxide. The lithium-manganese composite oxide according to claim 1, which has one or more of the following features (1) to (2).
(1) The spinel structure is included in the range of 20% by mass or less.
(2) The spinel structure is included in the range of 10% by mass or more. _3. The method according to claim 1 or ₂ , wherein the molar ratio M2/M1 between the number of moles M2 of the basic composition formula _Li2MnO3 and the number of moles M1 of the basic composition formula LiMnO2 is in the range of more than 10/90 and less than 60/40. lithium-manganese composite oxide. Basic composition formula Li _(2+2x)/(2+x) Mn _{(2/(2+x))- y My} O ₂ (where 0.1<x<0.6, M is Ti, Al and The lithium-manganese composite oxide according to any one of claims 1 to 3, wherein at least one of Fe is represented by 0≤y≤0.2). A positive electrode having the lithium manganese composite oxide according to any one of claims 1 to 4 as a positive electrode active material;
a negative electrode having a negative electrode active material;
an ion conducting medium interposed between the positive electrode and the negative electrode and conducting lithium ions;
Lithium secondary battery with A method for producing a lithium-manganese composite oxide used as an electrode active material for a lithium secondary battery, comprising:
A molar ratio M2/ between the number of moles M2 of basic composition formula Li ₂ MnO ₃ and the number of moles M1 of basic composition formula LiMnO ₂ obtained by firing in the range of 800° C. to 1100° C. and 6 hours to 15 hours. Raw materials are blended so that M1 is in the range of more than 10/90 and less than 60/40, and mixed and pulverized in the range of 20 hours or more and 40 hours or less to obtain the spinel structure including the rock salt structure and the spinel structure. is adjusted to be contained in the range of 5% by mass or more and 35% by mass or less,
A method for producing a lithium-manganese composite oxide containing In the adjustment step, the basic composition formula Li _(2+2x)/(2+x) Mn _{(2/(2+x))- y My} O ₂ (where 0.1<x<0.6, M is any one or more of Ti, Al and Fe, and the method for producing a lithium-manganese composite oxide according to claim 6, wherein the raw materials are blended so that 0≤y≤0.2).

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