TWI726967B - Lithium iron manganese composite oxide - Google Patents

Abstract

To provide a novel compound effective as a positive electrode active material for lithium ion secondary batteries. A lithium-iron-manganese composite oxide represented by the following composition formula: Li _1+m Fe _x Mn _2-x O ₄ [In the formula, m represents 0<m≦2, and x represents 0<x≦1].

Description

Lithium iron manganese composite oxide

Field of the Invention The present invention relates to lithium iron manganese composite oxides.

BACKGROUND OF THE INVENTION Lithium-ion secondary batteries occupy the most important position in energy storage devices, and their use has gradually expanded to plug-in hybrid car batteries in recent years.

Regarding the positive electrode of lithium ion secondary batteries, LiCoO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and other positive electrode active materials are currently the mainstream (Non-Patent Documents 1 and 2). However, the positive electrode material containing the positive electrode active material contains a large amount of rare metals such as cobalt and nickel, so the price is high, and the combustion-supporting ability is strong, so it is also one of the main causes of heat accidents.

In view of this, for the current positive electrode active materials that can solve this problem, iron-based poly(oxo)anion materials, especially LiFePO _4, have attracted attention (Non-Patent Document 3). The aforementioned iron-based poly(oxo)anion materials have attracted much attention (Non-Patent Document 3). The poly(oxygen) anion system utilizes the element iron rich in nature, and the strong polyvalent anion acid skeleton greatly suppresses the combustion-supporting property. Prior Art Literature Non-Patent Literature

Non-Patent Document 1: Solid State Ionics, 3-4, 171-174, 1981 Non-Patent Document 2: J.　Electrochem.　Soc.,　151(6),　A914-A921,　2004 Non-Patent Literature 3: J.　Electrochem.　Soc .,　144(4),　1188-1194,　1997

SUMMARY OF THE INVENTION Problems to be solved by the invention However, LiFePO ₄ can only be reversibly inserted and removed from 1 Li ⁺ part per molecule, so the charge and discharge capacity is low. In order to achieve high charge and discharge capacity, a positive electrode active material ^{that can be removed and inserted more than 1 Li + is required.}

The present invention has been implemented in view of these current conditions, and its object is to provide a novel compound that is effective as a positive electrode active material for lithium ion secondary batteries. Means to solve the problem

In order to solve the above-mentioned problems of the present invention, the inventors of the present invention continue to repeat intensive research. As a result, a lithium-iron-manganese composite oxide with a specific composition was successfully synthesized. In addition, we found that the lithium-iron-manganese composite oxide is feasible for insertion and removal of lithium ions, and exhibits a high theoretical charge-discharge capacity that can be used as a positive electrode active material for lithium-ion secondary batteries. Based on these findings, the inventors have further researched and completed the present invention.

That is, the representative of the present invention includes the subjects described in the following items. Item 1. A lithium-iron-manganese composite oxide, expressed by the following composition formula: Li _1+m Fe _x Mn _2-x O ₄ [where m means 0<m≦2, x means 0<x≦1] . Item 2. The lithium iron manganese composite oxide described in Item 1 above, which has a tetragonal crystal structure or a cubic crystal structure. Item 3. The lithium iron manganese composite oxide described in Item 1 or 2 above, which has a rock salt structure. Item 4. The lithium iron manganese composite oxide described in any one of items 1 to 3 above has an average particle size of 0.01 to 50 μm. Item 5. A method for producing a lithium iron manganese composite oxide as described in any one of items 1 to 4, comprising the step of heating a mixture containing lithium, iron, manganese, and oxygen. Item 6. The method described in Item 5 above, wherein the heating temperature is 600°C or higher. Item 7. A positive electrode active material for a lithium ion secondary battery, which contains the lithium iron manganese composite oxide described in any one of items 1 to 4 above. Item 8. A positive electrode for a lithium ion secondary battery, which contains the positive electrode active material for a lithium ion secondary battery as described in Item 7 above. Item 9. The positive electrode for a lithium ion secondary battery as described in Item 8, which further contains a conductive auxiliary agent. Item 10. A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery as described in Item 8 or 9 above. Invention effect

The lithium iron manganese composite oxide of the present invention can detach and insert more than one lithium ion, so it can be used as a positive electrode active material for lithium ion secondary batteries. In particular, by using the lithium iron manganese composite oxide of the present invention as a positive electrode active material, a lithium ion secondary battery that can exhibit high charge and discharge capacity can be produced.

Modes for Carrying Out the Invention The present invention will be described in detail below. However, when the numerical range is displayed in this specification, the numerical range includes the values at both ends.

1. Lithium-iron-manganese composite oxide The lithium-iron-manganese composite oxide of the present invention is a compound represented by the following composition formula: Li _1+m Fe _x Mn _2-x O ₄ [In the formula, m means 0＜m≦ 2. x represents 0<x≦1]. In addition, the compound may be described as the "compound of the present invention" below.

In the above composition formula, m is 0<m≦2. From the viewpoints of the ease of insertion and removal of lithium ions and the capacity and potential, 0<m≦1.5 is preferable, 0.5≦m≦1.5 is preferable, and 0.75≦m ≦1.25 is better. x is 0<x≦1. From the viewpoints of the ease of insertion and removal of lithium ions, capacity and potential, 0.25≦x≦1 is preferable, 0.5≦x≦1 is preferable, and 0.75≦x≦1 is more preferable .

Specifically, the compound of the present invention includes Li ₂ FeMnO ₄ .

The crystalline structure of the compound of the present invention is preferably a tetragonal crystal structure or a cubic crystal structure, and a tetragonal crystal structure is preferred. In particular, the compound of the present invention preferably has a tetragonal crystal structure or a cubic crystal structure as the main phase, and preferably has a tetragonal crystal structure as the main phase. In the compound of the present invention, the amount of the crystal structure of the main phase is not particularly limited, and it is preferably 80 mol% or more, preferably 90 mol% or more based on the entire compound of the present invention. Therefore, the compound of the present invention can be made into a material composed of a single-phase crystal structure, or can be made into a material having other crystal structures within the range that does not impair the effect of the present invention. In addition, the crystal structure of the compound of the present invention can be confirmed by X-ray diffraction measurement. In addition, when the compound of the present invention has a tetragonal crystal structure, a rock salt type structure is preferred.

The compound of the present invention has sharp peaks at various positions in the X-ray diffraction pattern using CuKα rays. For example, it is advisable to have peak values at the following diffraction angles 2θ: 18-20°, 37-39°, 43-45°, 61-68°, 70-77°, 78-82°, etc. Among them, it should have the highest peak at 43~45° and the second highest peak at 61~68°.

The average particle size of the compound of the present invention is not particularly limited. From the viewpoint of performance improvement, it is preferably 0.01-50 μm, preferably 0.1-50 μm, and more preferably 0.5-25 μm. In addition, the average particle size of the compound of the present invention can be confirmed by scanning electron microscope (SEM).

2. Production method of lithium iron manganese composite oxide The production method of the compound of the present invention includes a step of heating a mixture containing lithium, iron, manganese, and oxygen. In addition, the production method of the compound of the present invention may be described as "the production method of the present invention" below.

In the method for producing the compound of the present invention, for obtaining a raw material compound containing a mixture of lithium, iron, manganese, and oxygen, as long as the final mixture contains lithium, iron, manganese, and oxygen in a predetermined ratio, for example, it can be used Lithium-containing compounds, iron-containing compounds, manganese-containing compounds, oxygen-containing compounds, etc.

There are no particular restrictions on the types of compounds such as lithium-containing compounds, iron-containing compounds, manganese-containing compounds, and oxygen-containing compounds. Each of four or more of the elements of lithium, iron, manganese, and oxygen may be used. Compounds are used in combination, or a compound containing two or more of lithium, iron, manganese, and oxygen can be used as a part of the raw material, and less than four compounds can be used in combination.

The raw material compounds are preferably compounds that do not contain metal elements (especially rare metal elements) other than lithium, iron, manganese, and oxygen. In addition, elements other than the respective elements of lithium, iron, manganese, and oxygen contained in the raw material compound can preferably be desorbed or volatilized by the heating treatment described later.

Specific examples of such raw material compounds include the following compounds.

Examples of lithium-containing compounds include: metallic lithium (Li); lithium oxide (Li ₂ O); lithium bromide (LiBr); lithium fluoride (LiF); lithium iodide (LiI); lithium oxalate (Li ₂ C ₂ O ₄ ) ; Lithium hydroxide (LiOH); Lithium nitrate (LiNO ₃ ); Lithium chloride (LiCl); Lithium carbonate (Li ₂ CO ₃ ) and so on.

Examples of iron-containing compounds include: metallic iron (Fe); iron oxide (II) (FeO), iron oxide (III) (Fe ₂ O ₃ ) and other iron oxides; iron (II) bromide (FeBr ₂ ), chlorine Iron (II) (FeCl ₂ ); Iron hydroxide (II) (Fe(OH) ₂ ), iron hydroxide (III) (Fe(OH) ₃ ) and other iron hydroxides; Iron carbonate (II) (FeCO ₃ ), iron carbonate such as iron (III) (Fe ₂ (CO ₃ ) ₃ ); iron (II) oxalate (FeC ₂ O ₄ ), etc.

Examples of manganese-containing compounds include: metallic manganese (Mn); manganese oxide (II) (MnO), manganese (IV) oxide (MnO ₂ ) and other manganese oxides; manganese hydroxide (II) (Mn(OH) ₂ ), Manganese (IV) hydroxide (Mn(OH) ₄ ) and other manganese hydroxides; manganese (II) carbonate (MnCO ₃ ) and other manganese carbonates; manganese (II) oxalate (MnC ₂ O ₄ ), etc.

Examples of oxygen-containing compounds include: lithium hydroxide (LiOH); lithium carbonate (Li ₂ CO ₃ ); iron oxides such as iron (II) (FeO) and iron (III) oxide (Fe ₂ O ₃ ); hydroxides Iron (II) (Fe(OH) ₂ ), iron hydroxide (III) (Fe(OH) ₃ ) and other iron hydroxides; iron (II) carbonate (FeCO ₃ ), iron (III) carbonate (Fe ₂ ( CO ₃ ) ₃ ) and other iron carbonates; iron (II) oxalate (FeC ₂ O ₄ ); manganese (II) oxide (MnO), manganese (IV) oxide (MnO ₂ ) and other manganese oxides; manganese (II) hydroxide ) (Mn(OH) ₂ ), manganese hydroxide (IV) (Mn(OH) ₄ ) and other manganese hydroxides; manganese carbonate (II) (MnCO ₃ ) and other manganese carbonates; manganese (II) oxalate (MnC ₂ O ₄ ) and so on.

In addition, hydrates can also be used for these raw material compounds.

In addition, the raw material compound used in the production method of the present invention may be a commercially available product, or may be appropriately synthesized and used. When synthesizing each raw material compound, the synthesis method is not particularly limited, and it can be carried out according to a known method.

The shape of the raw material compounds is not particularly limited. From the viewpoint of ease of disposal, etc., powder form is preferable. In addition, from the viewpoint of reactivity, the particles are preferably fine, and the average particle size is preferably 1 μm or less (preferably about 10 to 200 nm, particularly preferably about 60 to 80 nm). In addition, the average particle size of the raw material compound can be measured by a scanning electron microscope (SEM).

By mixing the necessary materials in the above-mentioned raw material compounds, a mixture containing lithium, iron, manganese, and oxygen can be obtained.

The mixing ratio of each raw material compound is not particularly limited, and it is preferable to mix it in such a way that the final product of the compound of the present invention has a composition. The mixing ratio of the raw material compound is preferably such that the ratio of each element contained in the raw material compound is the same as the ratio of each element in the resulting compound of the present invention.

The method for preparing a mixture containing lithium, iron, manganese, and oxygen is not particularly limited, and a method that can uniformly mix the respective raw material compounds can be adopted. For example, it can be used: milk pottery mixing, mechanical grinding treatment, co-precipitation method, the method of dispersing each raw material compound in a solvent and then mixing, the method of dispersing and mixing each raw material compound in the solvent together, etc. Among them, the mixture can be obtained in a simpler way by mixing with milk ware, and a more uniform mixture can be obtained by co-precipitation method.

In addition, when performing mechanical grinding treatment as a mixing means, the mechanical grinding device can use, for example, a ball mill, a vibration mill, a turbine mill, a disc mill, etc., among which a ball mill is suitable. In addition, when performing mechanical grinding treatment, mixing and heating should be performed at the same time.

The gas environment during mixing and heating is not particularly limited as long as it is an inert gas environment. For example, an inert gas environment such as argon and nitrogen, and a hydrogen environment can be used. In addition, mixing and heating may be performed under reduced pressure such as a vacuum.

When heating a mixture containing lithium, iron, manganese, and oxygen, the heating temperature is not particularly limited. From the viewpoint of further improving the crystallinity and electrode characteristics (capacity and potential) of the compound of the present invention, it is preferable to set 600°C. Above, 700°C or higher is preferred, 800°C or higher is more preferred, and 900°C or higher is particularly preferred. In addition, the upper limit of the heating temperature is not particularly limited, and only a temperature (for example, about 1500°C) at which the compound of the present invention can be easily produced. In other words, the heating temperature should be set to 600~1500°C, 700~1500°C is better, 800~1500°C is more preferred, and 900~1500°C is especially preferred.

3. Positive electrode active material for lithium ion secondary batteries The compound of the present invention has the above composition and crystal structure, so it can insert and desorb lithium ions, so it can be used as a positive electrode active material for lithium ion secondary batteries. Therefore, the present invention includes a positive electrode active material for a lithium ion secondary battery containing the above-mentioned compound of the present invention. In addition, the positive electrode active material for lithium ion secondary batteries containing the compound of the present invention may be described as "the positive electrode active material of the present invention" below.

The positive electrode active material of the present invention may also form a composite of the compound of the present invention described above and a carbon material (for example, a material such as carbon black such as acetylene black). Thereby, the carbon material can suppress particle growth during firing, and therefore, a positive electrode active material for a lithium ion secondary battery of fine particles with excellent electrode characteristics can be obtained. At this time, the content of the carbon material in the positive electrode active material for lithium ion secondary batteries of the present invention is preferably 1-30% by mass, more preferably 3-20% by mass, and particularly preferably 5-15% by mass.

The positive electrode active material of the present invention contains the above-mentioned compound of the present invention. The positive electrode active material of the present invention may be composed only of the above-mentioned compound of the present invention, or it may contain unavoidable impurities in addition to the compound of the present invention. Such unavoidable impurities can be exemplified by the above-mentioned raw material compounds. The unavoidable impurity content is 10 mol% or less, preferably 5 mol% or less, and more preferably 2 mol% or less, within a range that does not impair the effect of the present invention.

4. Positive electrode for lithium ion secondary battery and lithium ion secondary battery The positive electrode for lithium ion secondary battery and lithium ion secondary battery of the present invention, in addition to using the compound of the present invention as the positive electrode active material, the basic structure can be adopted and known The positive electrode for a non-aqueous electrolyte (non-aqueous) lithium ion secondary battery and the non-aqueous electrolyte (non-aqueous) lithium ion secondary battery have the same configuration. For example, the positive electrode, the negative electrode, and the separator can be arranged in the battery container in such a manner that the positive electrode and the negative electrode are separated from each other through the separator. Then, the lithium ion secondary battery of the present invention is manufactured by filling the battery container with a non-aqueous electrolyte solution and then sealing the battery container. In addition, the lithium ion secondary battery of the present invention may also be a lithium secondary battery. In this specification, "lithium ion secondary battery" refers to a secondary battery that uses lithium ions as carrier ions, and "lithium secondary battery" refers to a secondary battery that uses lithium metal or lithium alloy as the negative electrode active material.

The positive electrode for a lithium ion secondary battery of the present invention can adopt a structure in which a positive electrode current collector supports a positive electrode active material containing the compound of the present invention. For example, a positive electrode material containing the above-mentioned compound of the present invention, a conductive auxiliary agent, and a binder on demand can be coated on a positive electrode current collector to be manufactured.

As the conductive auxiliary agent, for example, carbon materials such as acetylene black, Ketjen black, carbon nanotube, vapor-phase carbon fiber, carbon nanofiber, black lead, and coke can be used. The shape of the conductive auxiliary agent is not particularly limited, and for example, a powder form can be used.

As the binder, for example, fluororesin such as polyvinylidene fluoride resin and polytetrafluoroethylene can be used.

The content of various components in the positive electrode material is not particularly limited, and can be appropriately determined in a wide range. For example, it is advisable to contain 50-95% by volume (especially 70-90% by volume) of the above-mentioned compound of the present invention, 2.5-25% by volume (especially 5-15% by volume) of conductive assistant and 2.5-25% by volume ( Especially 5~15% by volume) of adhesives.

Examples of materials constituting the positive electrode current collector include aluminum, platinum, molybdenum, and stainless steel. The shape of the positive electrode current collector can be exemplified by porous bodies, foils, plates, and meshes composed of fibers.

In addition, the coating amount of the positive electrode material of the positive electrode current collector is not particularly limited, and it should be appropriately determined according to the use of the lithium ion secondary battery and the like.

The negative electrode active material constituting the negative electrode may include: lithium metal; silicon; silicon-containing crystal cage (Clathrate) compound; lithium alloy; M ¹ M ² ₂ O ₄ (M ¹ : Co, Ni, Mn, Sn, etc., M ² : Ternary or quaternary oxides shown in Mn, Fe, Zn, etc.; M ³ ₃ O ₄ (M ³ : Fe, Co, Ni, Mn, etc.), M ⁴ ₂ O ₃ (M ⁴ : Fe, Co, Oxidation of metals such as Ni, Mn, etc.), MnV ₂ O ₆ , M ⁵ O ₂ (M ⁵ : Sn, Ti, etc.), M ⁶ O (M ⁶ : Fe, Co, Ni, Mn, Sn, Cu, etc.) Materials; black lead, hard carbon, soft carbon, graphene; the above-mentioned carbon materials; Li ₂ C ₆ H ₄ O ₄ , Li ₂ C ₈ H ₄ O ₄ , Li ₂ C ₁₆ H ₈ O ₄ and other organic compounds.

Examples of lithium alloys include alloys containing lithium and aluminum as constituent elements, alloys containing lithium and zinc as constituent elements, alloys containing lithium and lead as constituent elements, alloys containing lithium and manganese as constituent elements, alloys containing lithium and bismuth Alloys as constituent components, alloys containing lithium and nickel as constituent elements, alloys containing lithium and antimony as constituent elements, alloys containing lithium and tin as constituent elements, alloys containing lithium and indium as constituent elements; alloys containing metal (scandium) , Titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, etc.) and carbon as constituent elements of MXene series alloys, M ⁷ _x BC ₃ series alloys (M ⁷ : Sc, Ti, V, Cr, Zr, Nb , Mo, Hf, Ta, etc.) and other quaternary system layered carbonized compounds or nitrided compounds.

The negative electrode can be composed of a negative electrode active material, and a negative electrode material can be supported on the negative electrode current collector. The negative electrode material contains a negative electrode active material, a conductive auxiliary agent and a binder on demand. When adopting the structure of supporting the negative electrode material on the negative electrode current collector, it can be manufactured by coating the negative electrode mixture containing the negative electrode active material, the conductive auxiliary agent and the binder on demand on the negative electrode current collector.

When the negative electrode is composed of a negative electrode active material, it can be obtained by shaping the above-mentioned negative electrode active material to conform to the shape (plate shape, etc.) of the electrode.

In addition, when the negative electrode material is supported on the negative electrode current collector, the types of the conductive auxiliary agent and the binder, and the content of the negative electrode active material, the conductive auxiliary agent, and the binder can be applied to the above-mentioned positive electrode. Examples of materials constituting the negative electrode current collector include aluminum, copper, nickel, and stainless steel. Examples of the shape of the aforementioned negative electrode current collector include porous bodies, foils, plates, meshes composed of fibers, and the like. In addition, the amount of the negative electrode material applied to the negative electrode current collector should be appropriately determined in accordance with the use of the lithium ion secondary battery.

The separator is not limited as long as it is made of a material that can isolate the positive electrode and the negative electrode in the battery, retain the electrolyte, and ensure the ionic conductivity between the positive electrode and the negative electrode. For example, polyolefin resins such as polyethylene, polypropylene, polyimide, polyvinyl alcohol, and terminally aminated polyethylene oxide; fluorine resins such as polytetrafluoroethylene; acrylic resins; nylon; aromatic aromatic amides; Inorganic glass; ceramic and other materials, using porous membranes, non-woven fabrics, woven fabrics and other materials.

The non-aqueous electrolyte is preferably an electrolyte containing lithium ions. Examples of such electrolytes include lithium salt solutions, ionic liquids composed of lithium-containing inorganic materials, and the like.

Examples of lithium salts include: lithium halides such as lithium chloride, lithium bromide, and lithium iodide; inorganic lithium salt compounds such as lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium hexafluoroarsenate; bis(trifluoromethylsulfonate) Lithium oxyimide, Lithium bis(perfluoroethanesulfonyl)imide, Lithium benzoate, Lithium salicylate, Lithium phthalate, Lithium acetate, Lithium propionate, Grignard reagent and other organic lithiums Salt compounds, etc.

In addition, the solvent may include carbonate compounds such as propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; γ-butyrolactone, γ-valerolactone, etc. Lactone compounds; tetrahydrofuran, 2-methyltetrahydrofuran, diethyl ether, diisopropyl ether, dibutyl ether, methoxymethane, ethylene glycol dimethyl ether (glyme), dimethoxyethane, two Methoxymethane, diethoxymethane, diethoxyethane, propylene glycol dimethyl ether and other ether compounds; acetonitrile; N,N-dimethylformamide; N-propyl-N-methylpyrrolidinium bis (Trifluoromethanesulfonyl) imide and the like.

In addition, a solid electrolyte may be used instead of the above-mentioned non-aqueous electrolyte. Examples of the solid electrolyte include lithium ion conductors such _{as Li 10 GeP 2} S ₁₂ , Li ₇ P ₃ S ₁₁ , Li ₇ La ₃ Zr ₂ O ₁₂ , and La _0.51 Li _0.34 TiO _2.94.

Because the lithium ion secondary battery of the present invention uses the compound of the present invention, it can ensure a higher potential and energy density during the oxidation-reduction reaction (charge-discharge reaction), and is safe (polyvalent anion skeleton) and practicality good. Therefore, the lithium ion secondary battery of the present invention is suitable for use in, for example, equipment that pursues miniaturization and high performance. Example

Hereinafter, the present invention will be explained in further detail with examples, but the present invention is not limited by the following examples.

Example 1: Synthesis of Li ₂ FeMnO ₄ raw material powder used Li ₂ CO ₃ (manufactured by RARE Metallic Co., Ltd.; 99.9% (3N)), Fe ₂ C ₂ O ₄ ･2H ₂ O (manufactured by Junsei Chemical Co., Ltd.) ; 99.9% (3N)) and MnO ₂ (manufactured by RARE METALLIC Co., Ltd.; 99.99% (4N)). After weighing Li ₂ CO ₃ , Fe ₂ C ₂ O ₄ ･2H ₂ O and MnO ₂ so that the ratio of lithium: iron: manganese (molar ratio) is 2:1:1, together with zirconia balls (15mmΦ×10) Put it in a chrome steel container, add acetone and pulverize and mix with a planetary ball mill (manufactured by Fritsch, trade name: P-6) at 400 rpm for 24 hours. Then, after removing the acetone under reduced pressure, the recovered powder was hand-rubbed into pellets, and fired at 600°C, 700°C, 800°C, 900°C, or 1000°C for 1 hour under argon gas flow. At this time, the temperature increase rate was set to 400°C/h. In addition, the cooling rate was set to 100°C/h up to 300°C, and then allowed to cool to room temperature by natural cooling. _{The obtained products (Li 2} FeMnO ₄ ) were confirmed by powder X-ray diffraction (XRD). The results are shown in Figure 1.

In addition, an X-ray diffraction measuring device (manufactured by Rigaku Corporation, trade name: RINT2200) was used for the powder X-ray diffraction (XRD) measurement system, and the X-ray source was CuKα monochromated by a monochromator. The measurement conditions were set to a tube voltage of 5 kV and a tube current of 300 mA to perform data collection. At this time, set the scanning speed so that the intensity becomes approximately 10,000 counts. In addition, the sample used for the measurement has been sufficiently crushed to make the particles uniform. The structural analysis department conducts Rietveld analysis, and the analysis software uses JANA-2006.

It is confirmed from Fig. 1 that when the firing temperature is 600°C or higher, many main peaks can be seen at least at a 2θ value of 30 to 65°. These peaks correspond to single-phase Li ₂ FeMnO ₄ , and it can be seen that single-phase Li ₂ FeMnO ₄ is obtained for the product. It is also known that the peak seen in the aforementioned 2θ value of 35~65° becomes stronger when the firing temperature is higher, so the firing temperature should be higher.

Moreover, it can be seen from Fig. 1 that the obtained Li ₂ FeMnO ₄ crystals have peaks in the X-ray diffraction pattern obtained by powder X-ray diffraction at the following diffraction angles shown in 2θ: 18-20°, 37-39°, 43 ~45°, 61~68°, 70~77° and 78~82°. From this result, the obtained Li ₂ FeMnO ₄ crystal system has a tetragonal structure (space group P4/nbm), and the lattice constants are a=b=3.596~3.610Å, c=14.366~14.498Å, α=β=γ =90°and the unit lattice volume (V) is a crystal of 187.2~187.5Å ³ . Also, from c/a=3.9950, it can be seen that the obtained Li ₂ FeMnO ₄ crystal has a rock salt structure.

Figure 2 shows another in the firing temperature was obtained Li ₂ FeMnO ₄ X-ray diffraction and other known-lithium-manganese composite oxide _{(Li 2 NiMnO 4, Li 2} CoMnO 4 and Li ₂ Mn ₂ O ₄₎ is at 800 ℃ Pattern comparison result. In addition, Li ₂ NiMnO ₄ , Li _{2 CoMnO 4,} and Li ₂ Mn ₂ O ₄ are samples synthesized by the same method as the above except that the raw material compound is replaced. _{Another, Li 2 FeMnO 4, Li 2} NiMnO 4, Li 2 CoMnO 4 and Li ₂ Mn ₂ O _4, and other iron manganese composite oxide _{(K 2 FeMnO 4, Na 2} FeMnO 4, MgFeMnO 4, LiFeMnO 4) each The comparison of lattice constants is shown in Table 1 below.

[Table 1]

Can be confirmed from FIG. _2, Li 2 FeMnO ₄ with other lithium-manganese composite oxide _{(Li 2 NiMnO 4, Li 2} CoMnO 4 and Li ₂ Mn ₂ O ₄₎ show completely different X-ray diffraction pattern.

_{In addition, Li 2} FeMnO ₄ obtained when the firing temperature was set to 800° C. was observed with a scanning electron microscope (SEM). The results are shown in Figure 3. In addition, the scale bar in FIG. 3 indicates 7.69 μm. It can be seen from Fig. 3 that Li ₂ FeMnO ₄ with a particle size of about 1-20 μm is obtained.

Example 2: Measurement of charge and discharge characteristics In order to perform charge and discharge measurements, the Li ₂ FeMnO ₄ , polyvinylidene fluoride (PVDF) and acetylene black (AB) obtained in the above-mentioned example 1 at a sintering temperature of 800°C were measured at a volume ratio of 85 : 7.5: 7.5 After mixing in an agate mortar, the resulting slurry is coated on the aluminum foil (thickness 20μm) of the positive electrode current collector and punched into a circle with a diameter of 8mm to make the positive electrode. In addition, in order to prevent the sample from peeling off the positive electrode current collector, pressure bonding was performed at 30-40 mPa.

The negative electrode uses 14mmφ perforated metal lithium, and the separator uses two 18mmφ perforated porous membranes (trade name: celgard 2500). The electrolyte is used: Ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed into a solvent at a volume ratio of 1:2, and _{LiPF 6} is dissolved ^{in the solvent at a concentration of 1 mol/dm 3} as a supporting electrolyte. Into the electrolyte solution (manufactured by Kishida Chemical Co., Ltd.). Due to the use of metallic lithium and the main reason for the increase in resistance if the electrolyte is mixed with moisture in the production of the battery, the battery was produced in a glove box under an argon atmosphere. The battery system uses the CR2032 coin type battery shown in Figure 4. The constant current charging and discharging measurement system uses a voltage switch at a charge-discharge rate of 0.05C or a charge-discharge rate of 0.1C. The current is set to 10mA/g, the upper limit voltage is 4.8V, and the lower limit voltage is 1.5V, starting from charging. In addition, the charge and discharge measurement is performed in a state where the battery is placed in a constant temperature bath at 55°C or at room temperature (25°C). The measurement results of charge-discharge characteristics at a charge-discharge rate of 0.05C (55°C) (relationship between each cycle and discharge capacity) are shown in Figure 5. The measurement results of charge-discharge characteristics at a charge-discharge rate of 0.05C (25°C) (each The relationship between cycle and discharge capacity) is shown in FIG. 6, and the measurement results of charge and discharge characteristics (relationship between each cycle and discharge capacity) at a charge-discharge rate of 0.1C (55°C) are shown in FIG. 7. In addition, the charge-discharge rate (C-rate) means the current density required to charge and discharge the electrode active material for 1 hour of theoretical capacity.

As shown in Figure 5, the initial charge capacity is 280mAh/g (approximately 1.9Li ⁺ parts) _{at a charge-discharge rate of 0.05C (55℃), and the theoretical capacity of Li 2} FeMnO ₄ is approximately 285mAh/g. Very close to the value of theoretical capacity. In addition, the average operating voltage is 2.8V, and the reversible charge-discharge capacity is about 250 mAh/g (about 1.8 Li ⁺ parts). This is equivalent to an energy density of 700Wh/kg, so Li ₂ FeMnO ₄ is highly expected as a positive electrode active material with high capacity and high energy density. In addition, it is confirmed from Fig. 6 that at room temperature, the capacity of 1 ^{Li + part can be reversibly detached and inserted at most.} From this result, it can be seen that Li ₂ FeMnO ₄ can exert its maximum performance by increasing the operating temperature. In addition, it can be seen from FIG. 7 that good cycle characteristics of initial discharge and high-order cycles can be obtained at a charge-discharge rate of 0.1C. It can be seen that the capacity that can be drawn at 0.1C charge and discharge rate is about 200mAh/g.

In addition, except that Li ₂ FeMnO _{4 was} not used, a positive electrode was produced in the same manner as described above, and a charge-discharge test was carried out at a C/20 charge-discharge rate (55° C.) under the same conditions as described above. The results are shown in Figure 8.

It was confirmed from FIG. 8 that the charge and discharge capacity could not be obtained in the electrode that _{did not use Li 2} FeMnO _4. Comparing FIG. 5 and FIG. 8, it can be seen that the high charge and discharge capacity shown in FIG. 5 is derived from Li ₂ FeMnO ₄ .

In addition, the charge-discharge rate characteristics _{of Li 2} FeMnO _{4 were studied.} Specifically, after charging at a charge rate of 0.05C, the initial discharge capacity at a discharge rate of 0.05C, a discharge rate of 0.1C, or a discharge rate of 0.2C is measured. The results are shown in Figure 9.

In Figure 9, the capacity obtained at a discharge rate of 0.1C is 225 mAh/g, and the capacity obtained at a discharge rate of 0.2C is 100 mAh/g. From these results, it can be seen that Li ₂ FeMnO ₄ shows good charge-discharge rate characteristics.

In addition, the current charge and discharge characteristics were measured in the same manner as the above except that the discharge was started at a charge and discharge rate of 0.05C. The results are shown in Figure 10.

In Fig. 10, _{the capacity extracted from Li 2} FeMnO ₄ after the initial discharge is about 360 mAh/g. From this result, it can be seen that as soon as Li ₂ FeMnO _{4 is} discharged for the first time, lithium is further inserted, and a higher capacity can be obtained. Therefore, Li ₂ FeMnO _{4 is} highly anticipated as a high-capacity positive electrode active material.

Comparative Example 1: _{Li 2} CO ₃ (manufactured by RARE Metallic Co., Ltd.; 99.9% (3N)), Fe ₂ O ₃ (Junsei Chemical, 99.9% (3N)) and MnO _{2 were} used for the _{synthesis of LiFeMnO 4 raw material powder} (RARE METALLIC Co., Ltd., 99.99%(4N)). Li ₂ CO ₃ , Fe ₂ O _3, and MnO _{2 were} weighed so that lithium:iron:manganese (molar ratio) became 1:1:2, and mixed in an agate mortar for about 30 minutes to obtain a raw material mixture. After that, the raw material mixture and zirconia balls (15 mmΦ×10 pieces) were put into a container made of chromium steel, and acetone was added to pulverize and mix with a planetary ball mill (Fritsch; P-6) at 400 rpm for 6 hours. Then, after acetone was distilled off under reduced pressure, the recovered powder was pelletized at 40 MPa and burned in air at 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, or 900°C. Into 3 hours. Then let it cool to room temperature by natural cooling. The obtained products were confirmed by powder X-ray diffraction (XRD) in the same manner as in Example 1. The results are shown in Figure 11.

It can be seen from Figure 11 that the obtained LiFeMnO ₄ crystal system has cubic crystals (space group Fd-3m), the lattice constant is a=b=c=8.286~8.306Å, α=β=γ=90° and the unit lattice volume (V) is a crystal of 568.9~573.0Å ³ . In addition, it can be seen from c/a=1 that the obtained LiFeMnO ₄ crystal has a spinel structure.

_{In addition, the LiFeMnO 4} obtained when the firing temperature was set to 800°C was observed with a scanning electron microscope (SEM). The results are shown in Figure 12. In addition, the scale bar in FIG. 12 indicates 1.53 μm. _{It can be seen from Fig. 12 that LiFeMnO 4} with a particle size of about 0.3 to 3 μm is obtained.

Comparative Example 2: Measurement of charge and discharge characteristics In order to perform charge and discharge measurements, the LiFeMnO ₄ , polyvinylidene fluoride (PVDF) and acetylene black (AB) obtained in the above Comparative Example 1 at a sintering temperature of 800°C were used in a volume ratio of 85:7.5 : 7.5 After mixing in an agate mortar, apply the resulting slurry to the aluminum foil (thickness 20μm) of the positive electrode current collector and punch it into a circle with a diameter of 8mm to make the positive electrode. In addition, in order to prevent the sample from peeling off the positive electrode current collector, pressure bonding was performed at 30-40 mPa.

The negative electrode uses 14mmφ perforated metal lithium, and the separator uses two 18mmφ perforated porous membranes (trade name: celgard 2500). Electrolyte system use: ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed into a solvent at a volume ratio of 1:2, and LiPF ₆ ^{is dissolved in the solvent at a concentration of 1 mol/dm 3} as a supporting electrolyte. Electrolyte (manufactured by Kishida Chemical Co., Ltd.). Due to the use of metallic lithium and the main reason for the increase in resistance if the electrolyte is mixed with moisture in the production of the battery, the battery was produced in a glove box under an argon atmosphere. The battery system uses the CR2032 coin type battery shown in Figure 4. The constant current charging and discharging measurement system uses a voltage switch at a charge and discharge rate of 0.05C. The current is set to 10mA/g, the upper limit voltage is 4.8V, and the lower limit voltage is 1.5V, starting from charging. In addition, the charge and discharge measurement was performed with the battery in a 55°C thermostat. The measurement results of initial charge-discharge characteristics at a charge-discharge rate of 0.05C (55°C) (relationship between each cycle and discharge capacity) are shown in Figure 13. The charge-discharge characteristics of high-level cycles at a charge-discharge rate of 0.05C (55°C) The measurement results (relationship between each cycle and discharge capacity) are shown in FIG. 14. In addition, the charge-discharge rate (C-rate) means the current density required to charge and discharge the electrode active material for 1 hour of theoretical capacity.

As shown in FIG. 13, it was confirmed that the spinel-type LiFeMnO ₄ had an initial charge-discharge capacity of 130 mAh/g at a charge-discharge rate of 0.05C. Comparing with the rock salt type Li ₂ FeMnO ₄ obtained in Example 1, it can be seen that the spinel type LiFeMnO _{4 has} an initial charge and discharge capacity much inferior to _{that of the rock salt type Li 2} FeMnO _4.

In addition, it can be seen from Fig. 14 that _{although the spinel-type LiFeMnO 4} has relatively stable operating characteristics, the extractable capacity is much inferior to _{that of the rock salt-type Li 2} FeMnO _4.

1‧‧‧Lithium-ion secondary battery 2‧‧‧Negative terminal 3‧‧‧Negative 4‧‧‧Separator soaked in electrolyte 5‧‧‧Insulation pad 6‧‧‧Positive electrode 7‧‧‧Positive can

FIG. 1 is a diagram showing the X-ray diffraction pattern of _{Li 2} FeMnO _{4 obtained in Example 1.} Figure 2 is a graph showing the comparison results of the following patterns: _{the X-ray diffraction pattern of Li 2} FeMnO ₄ obtained when the firing temperature is set to 800 ℃ in Example 1 is compared with other lithium manganese composite oxides (Li ₂ NiMnO ₄ , Li ₂ CoMnO ₄ and Li ₂ Mn ₂ O ₄ ) X-ray diffraction patterns. Fig. 3 is a diagram showing the result of observing the _{Li 2 FeMnO 4} obtained when the firing temperature in Example 1 is set to 800° C. with a scanning electron microscope (SEM). 4 is a cross-sectional view of the test battery used in Example 2. FIG. Fig. 5 is a graph showing the measurement results of the charge and discharge characteristics performed in Example 2 (0.05C charge and discharge rate; 55°C). Fig. 6 is a graph showing the measurement results of the charge and discharge characteristics performed in Example 2 (charge and discharge rate at 0.05C; 25°C). FIG. 7 is a graph showing the measurement results of the charge-discharge characteristics (0.1C charge-discharge rate) performed in Example 2. FIG. FIG. 8 shows the measurement results of the charge and discharge characteristics of only carbon and PVDF electrodes performed in Example 2. FIG. 9 is a graph showing the measurement results of the charge-discharge rate characteristics performed in Example 2. FIG. FIG. 10 is a graph showing the measurement results of the charge and discharge characteristics (0.05C charge and discharge rate) performed in Example 2. FIG. In addition, it is the result from the beginning of the discharge. 11 is a diagram showing the X-ray diffraction pattern of _{LiFeMnO 4 obtained in Comparative Example 1.} Fig. 12 is a diagram showing the result of _{observing the LiFeMnO 4} obtained when the firing temperature is 800° C. in Comparative Example 1 with a scanning electron microscope (SEM). Fig. 13 shows the measurement results of initial charge-discharge characteristics performed in Comparative Example 2 (0.05C charge-discharge rate; 55°C). Fig. 14 shows the measurement results of the charge-discharge characteristics under high-level cycles in Comparative Example 2 (0.05C charge-discharge rate; 55°C).

(no)

Claims (8)

A lithium-iron-manganese composite oxide with a rock salt structure and represented by the following composition formula: Li _1+m Fe _x Mn _2-x O ₄ [where m means 0<m≦2, x means 0< x≦1]. For example, the lithium-iron-manganese composite oxide of claim 1 has an average particle size of 0.01-50μm. A method for manufacturing a lithium iron manganese composite oxide is to manufacture the lithium iron manganese composite oxide as claimed in claim 1 or 2. The manufacturing method includes the step of heating a mixture containing lithium, iron, manganese and oxygen. Such as the method of claim 3, the heating temperature is 600°C or higher. A positive electrode active material for a lithium ion secondary battery, which contains the lithium iron manganese composite oxide as claimed in claim 1 or 2. A positive electrode for a lithium ion secondary battery, which contains the positive electrode active material for a lithium ion secondary battery according to claim 5. For example, the positive electrode for lithium ion secondary battery of claim 6, which further contains a conductive auxiliary agent. A lithium ion secondary battery containing the positive electrode for a lithium ion secondary battery as in Claim 6 or 7.

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