WO2018181967A1 - Manganese oxide, production method therefor, and lithium secondary battery - Google Patents

Abstract

Provided are a novel manganese oxide suitable for a positive electrode material for a high-energy-density lithium secondary battery, a production method for the manganese oxide, and a high-energy-density lithium secondary battery. This manganese oxide is represented by general formula Li(4/3-X-Y)M(2/3+X)O2 (0≤X≤1/3, 0<Y≤4/3, M represents only Mn and Ni, and 0< Ni/Mn molar ratio ≤2/5), and has a crystalline structure belonging to the monoclinic crystal system (space group: C2/m). This manganese oxide production method comprises electrochemically oxidizing and reducing a lithium-containing manganese oxide that is represented by general formula Li(4/3-X)M(2/3+X)O2 (0≤X≤1/3, M represents only Mn and Ni, and 0 < Ni/Mn molar ratio ≤ 2/5), that has a BET specific surface area of 0.5 m2/g or less and a primary particle size of 0.5 μm or more, and that has a crystalline structure belonging to the monoclinic crystal system (space group: C2/m). This lithium secondary battery has a positive electrode containing the manganese oxide.

Description

Manganese oxide, method for producing the same, and lithium secondary battery

The present invention relates to a manganese oxide, a method for producing the same, and a lithium secondary battery using the same.

Lithium secondary batteries are widely used as storage batteries for mobile terminals because they have a higher energy density than other storage batteries. Recently, application to a large-sized application requiring a large capacity such as a stationary one and an in-vehicle one has been promoted.

As a positive electrode material of a lithium secondary battery aiming at high energy density, NCM material (patent document 1) consisting of lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and oxygen, Li NCA material (Patent Document 2) made of Ni, aluminum (Al), Co, and oxygen is used. All of these materials belong to R3-m having a layered structure in which a layer occupied by Li and a layer occupied by a metal element other than Li are alternately stacked with a layer occupied by oxygen interposed therebetween. It is a layered rock salt crystal compound. Structurally, when NCM or NCA removes 80% or more of Li contained by charging, electrostatic repulsion between oxygen layers is strengthened, the crystal structure is irreversibly changed, and the charge / discharge capacity is greatly reduced. For this reason, the electrochemical capacity is at most about 80% of the electrochemical capacity calculated from the Li content, and the discharge capacity of 200 to 220 mAh / g is the upper limit for practical use.

Studies have been conducted on the use of Li ₂ MnO ₃ with the aim of further increasing the energy density of the positive electrode material. Since Li ₂ MnO ₃ has a Li-excess composition compared to NCA and NCM, a high capacity is expected.
Li ₂ MnO ₃ in the Li-rich Mn oxide is labeled Li [Li _1/3 Mn _2/3 ] O ₂ and is an orthorhombic system in the space group C2 / m of the layered rock-salt crystal with Li-rich composition. Belonging to. Since the composition of Li is excessive, the symmetry of the crystal is lower than that of the layered rock salt type crystal, and in addition to the diffraction peak of the layered rock salt type crystal, a diffraction pattern corresponding to the lowering of the symmetry is characteristic. In powder X-ray diffraction measurement using CuKα rays, a unique diffraction pattern is shown in a region where the diffraction angle 2θ is 20 ° to 35 °.

Since Li ₂ MnO ₃ has a Li-excess composition compared to NCA and NCM, a high capacity is expected. However, in reality, a high discharge capacity of 250 mAh / g can be obtained in the initial stage, but it has been reported that a rapid capacity drop occurs as the charge / discharge cycle proceeds. It is thought that the cause of the large decrease in capacity with respect to the cycle is related to the transition of the crystal phase to the cubic spinel phase (Fd3-m) due to the release of oxygen generated during charging and the accompanying movement of the transition metal element in the crystal structure. (Non-Patent Document 1).

The valence of Mn contained in Li ₂ MnO ₃ is +4, and in the charge / discharge reaction of Li ₂ MnO ₃ , oxygen ions compensate for the charge. The oxygen ion O ²⁻ is known to be oxidized to the O ₂ state via the peroxidized state O ₂ ²⁻ , and therefore the ideal charge / discharge reaction of Li ₂ MnO ₃ is as follows: Can be considered.
Li ₂ Mn ⁴⁺ O ₃ ⇔Mn ⁴⁺ O ₂ + 2Li ⁺ + 2e ⁻ + 1 / 2O ₂ (Formula 1)

If during the oxygen ions O in the crystal lattice ^2- charging undergoing oxidation to a state of O _2, oxygen atom is considered possible that easily separated from the crystal lattice. It is difficult for oxygen once desorbed to be taken into the crystal lattice again by a reduction reaction at the time of discharge, and the capacity decreases corresponding to the desorption of oxygen. When oxygen is released from the crystal lattice, other constituent elements such as Mn and Li easily move to the site occupied by the oxygen vacated by the separation, and the crystal phase changes due to the movement. In Li ₂ MnO ₃ , it is considered that the crystal phase changes to a spinel phase with a charge / discharge cycle, and a sudden capacity drop occurs correspondingly.

On the other hand, since Li ₂ MnO ₃ belongs to the same layered rock salt type crystal system except that it has a Li-excess composition, it is possible to form a solid solution with the layered rock salt type crystal system compound. For example, Ni excess composition Ni, Co, which can be regarded as a solid solution with lithium nickel manganese oxide (LiNi _1/2 Mn _1/2 O ₂ ) of NCM or layered rock salt type crystal system, Ni, Mn oxide or Li excess composition, Mn oxide has been studied. The valences of Ni and Co in the solid solution are theoretically +2 and +3, respectively, and Mn has the same +4 valence as Mn in Li ₂ MnO ₃ and maintains a high capacity property.

The study of the solid solution described above aims to achieve both the high capacity characteristic originally provided by Li ₂ MnO ₃ and the reversibility provided by NCM and lithium nickel manganese oxide. Although a high discharge capacity can be obtained, the capacity drop with respect to the charge / discharge cycle is still large compared to NCM, Li, Ni, and Mn oxide (Non-patent Document 2), and it is a problem to suppress oxygen desorption and crystal phase change. It becomes.

A method has been proposed in which calcium (Ca) and magnesium (Mg), which are highly covalently bound to oxygen, are introduced into the structure of Ni and Mn oxides with an excess of Li to suppress the release of oxygen during charging. (Patent Document 3).
It is known that the oxygen desorption reaction forms a potential flat at about 4.5 V with respect to lithium at the time of initial charge, but Ni in the Li-rich composition and part of Li in the Mn oxide are replaced with Ca or Mg. Then, a potential flat portion of 4.5 V is not recognized, and it is shown that the detachment of oxygen can be suppressed. As a result, even when charging and discharging are repeated, the space structure C2 / m is maintained in the crystal structure, and a charging / discharging capacity of 250 to 300 mAh / g is stably obtained.

Patent Document 3 is a proposal that shows that a high capacity can be stably expressed if the release of oxygen can be suppressed. Generally, when an element having a large ion radius such as Ca is introduced into the Li layer, the charge / discharge Li There is also a possibility that the diffusion in the solid phase may be inhibited, and there is a concern that the capacity may decrease due to a decrease in the amount of Li due to substitution.

JP 2010-015959 A JP 2010-080394 A International Publication No. 2016/190251

An object of the present invention is to provide a manganese oxide having a Li-excess composition that stably expresses a high capacity without substitution with a different element such as Ca and Mg, and a method for producing the same. The present invention provides a lithium secondary battery having a high energy density in which is used for a positive electrode.

The inventors of the present invention have made extensive studies on a manganese oxide having an excessive Li composition. As a result, it has been found that the present invention having the following summary can achieve the above-described problems.
(1) General formula Li _{(4 / 3-XY)} M _{(2/3 + X)} O ₂ (where 0 ≦ X ≦ 1/3, 0 <Y ≦ 4/3, M is only Mn and Ni) And 0 <Ni / Mn molar ratio ≦ 2/5.) And a crystal structure belonging to a monoclinic crystal (space group C2 / m).
(2) In the above general formula, 1/20 ≦ X ≦ 1/8, 0.7 ≦ Y ≦ 1.0, and 0 <Ni / Mn molar ratio ≦ 1/3 (1 ) Manganese oxide.
(3) The manganese oxide according to (1) or (2), which includes two phases having different lattice constants.

(4) The method for producing a manganese oxide according to any one of the above (1) to (3), wherein the general formula Li _{(4 / 3-X)} M _{(2/3 + X)} O ₂ (where , 0 ≦ X ≦ 1/3, M is only Mn and Ni, or Mn, Ni and Mn, and 0 <Ni / Mn molar ratio ≦ 2/5 is satisfied.], And the BET surface area is 0.5 m. ² / g or less, a primary particle diameter of 0.5 μm or more, and a lithium-containing manganese oxide belonging to a monoclinic crystal (space group C2 / m) is subjected to electrochemical oxidation / reduction. The manufacturing method characterized by the above-mentioned.
(5) The manufacturing method according to (4), wherein, in the general formula, 1/20 ≦ X ≦ 1/8 and 0 <Ni / Mn molar ratio ≦ 1/3 is satisfied.
(6) The production method according to (4) or (5), wherein the lithium-containing manganese oxide has a BET specific surface area of 0.1 to 0.4 m ² / g.
(7) The production method according to any one of (4) to (6), wherein a primary particle diameter of the lithium-containing manganese oxide is 0.5 to 1.0 μm.
(8) The electrochemical oxidation / reduction is performed through charging / discharging in a lithium battery using a positive electrode using the lithium-containing manganese oxide, according to any one of (4) to (7) above. Production method.
(9) The production method according to (6), wherein a lithium battery using a positive electrode using the lithium-containing manganese oxide can be used as a lithium secondary battery as it is.
(10) A lithium secondary battery comprising a positive electrode containing the manganese oxide described in any one of (1) to (3) above.

When the manganese oxide of the present invention is used as a positive electrode material for a lithium secondary battery, it can be charged / discharged with an extremely high capacity compared to the conventional lithium secondary battery having a high energy density. Provision becomes possible.
In addition, the method for producing manganese oxide of the present invention can efficiently produce the above-mentioned book by electrochemically oxidizing and reducing the raw material lithium manganese oxide, preferably through charge / discharge in a lithium battery using this as a positive electrode. Enables the production of the manganese oxides of the invention.

2 is a powder X-ray diffraction pattern of the lithium-containing manganese oxide obtained in Example 1. 3 is a powder X-ray diffraction pattern of each lithium-containing manganese oxide obtained in Examples 2 to 4. FIG. It is a powder X-ray-diffraction pattern in the discharge state after repeating the charge / discharge cycle of the coin cell in Example 2 25 times.

It is the charge / discharge profile after repeating the charge / discharge cycle of the coin cell in Example 2 25 times, and the initial charge / discharge cycle profile of the NCM of the reference example (Reference). 4 is a SEM image of each lithium-containing manganese oxide in Examples 1 to 4. It is a Rietveld crystal structure analysis of the synchrotron radiation X-ray diffraction measurement after repeating the charge / discharge cycle of the coin cell in Example 6 20 times. It is a Rietveld crystal structure analysis of the synchrotron radiation X-ray diffraction measurement after repeating the charge / discharge cycle of the coin cell in Example 7 30 times.

Hereinafter, the present invention will be described in more detail.
The manganese oxide of the present invention is represented by the general formula Li _{4 / 3-XY} M _{2/3 + X} O ₂ . Here, 0 ≦ X ≦ 1/3, preferably 1/20 ≦ X ≦ 2/15, and particularly preferably 1/20 ≦ X ≦ 1/8. 0 <Y ≦ 4/3, and preferably 0.7 ≦ Y ≦ 1.0. M is only Mn and Ni and satisfies 0 <Ni / Mn molar ratio ≦ 2/5.

The value of the Ni / Mn molar ratio in the general formula Li _{4 / 3-XY} M _{2/3 + X} O _{2 which} is the manganese oxide of the present invention is a raw material used in the method for producing a manganese oxide of the present invention. It can be determined from a composition analysis of the general formula Li _{(4 / 3-X)} M _{(2/3 + X)} O ₂ which is a lithium-containing manganese oxide. Examples of the method include dielectric coupling plasma emission analysis and atomic absorption analysis.

The value of Y in the general formula Li _{4 / 3-XY} M _{2/3 + X} O ₂ , which is the manganese oxide of the present invention, corresponds to the amount of Li desorption by electrochemical oxidation / reduction. It can be calculated by using Coulomb's law from the quantity of electricity at the time of selective oxidation / reduction.
The crystal structure of the general formula Li _{4 / 3-XY} M _{2/3 + X} O ₂ which is the manganese oxide of the present invention can be identified by powder X-ray diffraction measurement.

The manganese oxide of the present invention has a crystal structure belonging to a monoclinic crystal (space group C2 / m). The mechanism is unknown, but this monoclinic crystal structure of the manganese oxide of the present invention reversibly reduces the electrostatic repulsion of oxygen when lithium is desorbed in large quantities and suppresses structural changes. Therefore, it is considered that a large amount of Li can be stably inserted and removed.

The manganese oxide of the present invention preferably contains two phases having different lattice constants. The mechanism is unknown, but the presence of two phases with different lattice constants relieves or cancels Li insertion / desorption with respect to charging / discharging and the expansion / contraction of crystals associated with redox of Ni, Mn, and oxygen. It is considered that stability is improved.

In the manganese oxide of the present invention, M is only Ni and Mn, and it is necessary to satisfy 0 <Ni / Mn molar ratio ≦ 2/5. When the Ni / Mn molar ratio exceeds 2/5, the crystal structure of Ni becomes difficult to maintain a monoclinic crystal, and the upper limit of the Ni / Mn molar ratio is 2/5. The Ni / Mn molar ratio is preferably 1/3 or less, particularly preferably 1/4 or less. On the other hand, the Ni / Mn molar ratio is preferably 1/8 or more, and particularly preferably 1/5 or more, in order to suppress the decrease in capacity due to the transition of the Ni valence to a +3 highly oxidized state.

The manganese oxide of the present invention has a BET specific surface area of 0.5 m ² / g or less and a primary particle diameter of 0.5 μm or more, and has the general formula Li _{(4 / 3-X)} M _{(2/3 + X)} O ₂ (where 0 ≦ X ≦ 1/3, M is only Mn and Ni, and 0 <Ni / Mn molar ratio ≦ 2/5 is satisfied), and the crystal structure is monoclinic (space It is obtained by electrochemically repeating oxidation / reduction of lithium-containing manganese oxide belonging to group C2 / m).
In the above general formula, preferably, 1/20 ≦ X ≦ 2/15, particularly preferably 1/20 ≦ X ≦ 1/8. Further, preferably, 1/8 ≦ Ni / Mn molar ratio ≦ 1/3.

By electrochemically repeating oxidation and reduction, a large amount of Li can be inserted and desorbed from the lithium-containing manganese oxide while maintaining the original monoclinic crystal structure. At this time, if the BET specific surface area of the lithium-containing manganese oxide is 0.5 m ² / g or less and the primary particle diameter is 0.5 μm or more, the detachment of oxygen that is likely to occur at the time of charging is suppressed, which is inherently high. The capacity property can be stably expressed.
The BET specific surface area of the lithium-containing manganese oxide is preferably 0.1 to 0.4 m ² / g, and the primary particle diameter is preferably 0.5 to 1.0 μm.

As a method for electrochemically oxidizing / reducing the lithium-containing manganese oxide, preferably, a method in which a battery is produced and charging and discharging are repeated in the battery is exemplified. Of course, instead of this, oxidation and reduction may be performed outside the battery.
As a method of producing a battery and charging / discharging the battery, a lithium battery is produced using the lithium-containing manganese oxide as a positive electrode material, and charging / discharging is performed in the battery.

As a configuration of the lithium battery in this case, a configuration that can be used as it is as a lithium secondary battery is preferable. Since it can be used as a battery as it is, a method of electrochemically oxidizing / reducing is preferably a method of producing a battery and repeating charging and discharging in the battery.
The monoclinic manganese oxide of the present invention can be obtained by electrochemically repeating oxidation and reduction of monoclinic lithium-containing manganese oxide.

The composition of the lithium-containing manganese oxide used in the production of the manganese oxide of the present invention can be determined from composition analysis. Examples of the method obtained from the composition analysis include dielectric coupling plasma emission analysis and atomic absorption analysis.

The BET specific surface area of the lithium-containing manganese oxide used in the production of the manganese oxide of the present invention is obtained by converting the adsorption isotherm obtained from physical gas adsorption into a BET plot, and based on the BET isotherm, the gas adsorption of the monolayer The amount Vm can be obtained and can be obtained by the so-called BET method in which the specific surface area is calculated based on the molecular size of the gas used for physical adsorption.

The primary particle diameter of the lithium-containing manganese oxide used in the production of the manganese oxide of the present invention can be determined from direct observation with a scanning electron microscope (SEM). Here, the primary particle diameter refers to particles in which crystallites are densely aggregated to form one particle.

The lithium-containing manganese oxide used in the manufacture of the manganese oxide of the present invention has a molar ratio of (Mn raw material + Ni raw material) to Li raw material] of 0 <[Li / (Mn + Ni) ratio] <2, and the Mn raw material and Ni The raw material molar ratio] is set to 0 <[Ni / Mn molar ratio] ≦ 2/5, and a mixture of Mn raw material, Ni raw material, and Li raw material in a solid phase, a liquid phase, or a combination of both is fired. Can be prepared.
Examples of the firing include a method in which the firing is performed in the air, preferably at 400 to 1000 ° C., preferably for 6 to 24 hours, but is not particularly limited as long as a monoclinic crystal structure can be obtained. Examples of the temperature increase and temperature decrease conditions during firing include temperature increase and decrease at a constant rate, and stepwise temperature increase and decrease, but are not limited thereto.

There is no restriction | limiting in particular in the Mn raw material used by manufacture of lithium containing manganese oxide. For example, manganese sulfate, manganese carbonate, manganese nitrate, manganese chloride, trimanganese tetroxide (Mn ₃ O ₄ ), MnO, Mn (OH) ₂ , Birnessite, Hollandite, Manganite, Romanite, Todorokite, acid treatment of these Mn raw materials Although a thing etc. are illustrated, it is not restrict | limited to these.

There is no particular limitation on the Ni raw material used in the production of lithium-containing manganese oxide. For example, nickel sulfate, nickel carbonate, nickel nitrate, nickel chloride, nickel hydroxide, nickel oxide and the like are exemplified, but not limited thereto.

In the production of the lithium-containing manganese oxide, it is possible to use an oxide prepared in advance so that Mn and Ni have the Ni / Mn molar ratio of the present invention. For example, hydroxide [(Mn · Ni) (OH) ₂ ], oxyhydroxide [(Mn · Ni) OOH] prepared beforehand so that Mn and Ni have the Ni / Mn molar ratio of the present invention, oxidation Examples include [[Mn · Ni) O, (Mn · Ni) O ₂ , (Mn · Ni) ₂ O ₃ , (Mn · Ni) ₃ O ₄ ], but are not limited thereto.

The Li raw material used in the production of the lithium-containing manganese oxide is not particularly limited, and examples include lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium iodide, lithium oxalate, lithium sulfate, and lithium oxide. However, it is not limited to these.
By using the manganese oxide of the present invention for the positive electrode of a lithium secondary battery, it becomes possible to constitute a high-capacity lithium secondary battery that could not be obtained conventionally.

The configuration of the lithium secondary battery other than the positive electrode is not particularly limited, but the negative electrode is a material that occludes and releases Li, for example, a carbon-based material, a tin oxide-based material, Li ₄ Ti ₅ O ₁₂ , SiO, Li, and the like. The material etc. which form an alloy are illustrated. Examples of the material that forms an alloy with Li include silicon-based materials and aluminum-based materials. Examples of the electrolyte include an organic electrolytic solution in which a Li salt and various additives are dissolved in an organic solvent, a Li ion conductive solid electrolyte, and a combination thereof.

Next, the present invention will be described with reference to specific examples, but the present invention should not be construed as being limited to these examples.
<Production of battery>
The lithium-containing manganese oxide obtained in each Example and a conductive binder (trade name: TAB-2, manufactured by Hosen Co., Ltd.) were mixed at a weight ratio of 2: 1 using an agate mortar. The obtained mixture was uniaxially pressed onto a SUS mesh (SUS316) having a diameter of 13 mmφ at 1 ton / cm ² to form a disk-shaped pellet, and then dried under reduced pressure at 150 ° C. for 2 hours to obtain a positive electrode.

Metallic lithium is used for the negative electrode, and 1 mol / dm ³ of LiPF ₆ dissolved in a 1: 2 volume ratio solvent of ethylene carbonate and dimethyl carbonate is used for the electrolyte, and a polyethylene sheet (trade name: Celgard, manufactured by Polypore) ) Was used as a separator to prepare a CR2032-type coin cell.

<Charge / discharge cycle test>
(1) Test conditions of Examples 1 to 5 Using the produced coin cell, the cell voltage was between 4.8 V and 2.0 V at room temperature (22 to 27 ° C.), and initially 10 mA / 4.8 to 4.8 V. The battery was charged at a current value of g and charged at 4.8 V for 4 hours after reaching 4.8 V. Subsequently, the battery was discharged to 2.0 V at a current value of 10 mA / g, and thereafter, this charge / discharge cycle was repeated to obtain the maximum discharge capacity.

(2) Test conditions of the reference example Using the manufactured coin cell, the battery voltage was first charged at a constant current of 10 mA / g and a cell voltage between 4.3 V and 2.5 V under room temperature conditions (22 to 27 ° C.). Then, the battery was discharged, and thereafter the charge / discharge cycle was repeated to obtain the maximum discharge capacity.

<Composition analysis>
The composition of the prepared lithium-containing manganese oxide was analyzed with a dielectric coupled plasma emission spectrometer (trade name: ICP-AES, manufactured by PerkinElmer Japan).

<Measurement of BET specific surface area>
1 g of a sample was put into a glass cell for measuring a BET specific surface area, and dehydrated at 150 ° C. for 1 hour under a nitrogen stream to remove water adhering to the powder particles.
The BET specific surface area is measured by a one-point method using a mixed gas of 30% nitrogen and 70% helium as an adsorbed gas using a BET measuring device (trade name: MiCROMERITIC DeSorbIII, manufactured by Shimadzu Corporation). did.

<Measurement of primary particle size>
Using a scanning electron microscope (trade name: JSM-6390LV, manufactured by JEOL Ltd.), observation was performed at an acceleration voltage of 20 kV, and a primary particle diameter was determined from a particle image observed at a magnification of 10,000 times.

<Evaluation of crystallinity>
(1) The crystallinity of the crystal structure of the lithium-containing manganese oxide prepared in Example 1 was identified using a powder X-ray diffractometer (trade name: RINT 2550V, manufactured by Rigaku). The measurement conditions were as follows.
・ Target: Cu ・ Output: 8.0 kW (200 mA-40 kV)
Step scan: 0.03 ° (2θ / θ) Measurement time: 2.0 seconds (2) Lithium-containing manganese oxide prepared in Examples 2 to 4, commercially available NCA used in Reference Examples, and Identification of the crystallinity of the crystal structure of NCM was performed using a powder X-ray diffractometer (trade name: Ultimate IV, manufactured by Rigaku). The measurement conditions were as follows.
・ Target: Cu ・ Output: 1.6 kW (40 mA-40 kV)
・ Step scan: 0.04 ° (2θ / θ) ・ Measurement time: 0.6 seconds

<Change in crystallinity after repeated charge / discharge cycles>
The coin cell after the charge / discharge cycle test was disassembled, the positive electrode was taken out, and the crystallinity of the manganese oxide was evaluated with a powder X-ray diffraction measurement apparatus (trade name: Ultimate IV, manufactured by Rigaku). The measurement conditions were as follows.
・ Target: Cu ・ Output: 1.6 kW (40 mA-40 kV)
Step scan: 0.04 ° (2θ / θ) Measurement time: 0.6 seconds <Crystal structure analysis of manganese oxide after repeated charge / discharge cycles>
The coin cell after the charge / discharge cycle test was disassembled, the positive electrode was taken out, and the crystallinity of the manganese oxide was evaluated by synchrotron radiation X-ray diffraction measurement. The measurement was performed at the Aichi Synchrotron Light Center, and the measurement conditions were as follows.
・ Measurement wavelength: 0.78 mm ・ Measurement resolution: 0.01 deg
Measurement method: Debye-Scherrer method Capillary material: Lindeman glass Using the obtained measurement data, Rietveld method crystal structure analysis was performed to determine the crystal structure.

Example of raw material production Nickel sulfate and manganese sulfate were dissolved in pure water to obtain an aqueous solution containing 0.5 mol / L (liter) of nickel sulfate and 1.5 mol / L of manganese sulfate. . The total concentration of all metals in the metal aqueous solution was 2.0 mol / L. Further, 200 g of pure water was put into a reaction vessel having an internal volume of 1 L, and then this was heated to 80 ° C. and maintained.

The metal salt aqueous solution was added to the reaction vessel at a supply rate of 0.28 g / min. Further, air was bubbled into the reaction vessel at a supply rate of 1 L / min as an oxidant. A 2 mol / L sodium hydroxide aqueous solution (caustic soda aqueous solution) was intermittently added so that the pH was 10 when supplying the metal salt aqueous solution and air to obtain a mixed aqueous solution. In the mixed aqueous solution, nickel-manganese composite oxyhydroxide was precipitated to obtain a slurry. The obtained slurry was filtered and washed, and then the wet cake after washing was air-dried in the air for 1 week, and then dried at 115 ° C. for 5 hours, thereby obtaining an oxyhydroxide containing Mn and Ni (Ni _0.245). Mn _0.755 OOH, Mn: 45.3 wt%, Ni: 14.7 wt%).

Example 1
1.80 g of oxyhydroxide containing Mn and Ni obtained in the above raw material production example and 1.21 g of commercially available lithium carbonate (manufactured by Rare Metallics) were dry-mixed for 15 minutes using a mortar. To the resulting mixture, 2 mL of ethanol (special grade reagent, manufactured by Kishida Chemical Co., Ltd.) was added and mixed for 60 minutes. 1.00 g of the obtained mixed powder was put in a baking dish, subjected to heat treatment at 900 ° C. for 12 hours in a box furnace, cooled to room temperature, and a sample was taken out. The temperature increase rate and temperature decrease rate were 300 ° C./hr. When the temperature was lowered, the furnace was cooled at 300 ° C. or lower.

From the evaluation of crystallinity and composition analysis of the sample prepared above, the obtained crystal belongs to monoclinic C2 / m, the Ni / Mn molar ratio is 0.304, and the Li / (Mn + Ni) molar ratio. Was 1.50. From these values, X was 0.13, and a lithium-containing manganese oxide of Li _1.20 M _0.80 O ₂ (Li _1.20 Mn _0.61 Ni _0.19 O ₂ ) was obtained. I understood. The lithium-containing manganese oxide had a BET specific surface area of 0.4 m ² / g and a primary particle size of 1 μm. The powder X-ray diffraction pattern of this lithium-containing manganese oxide is shown in FIG.

A coin cell using the obtained lithium-containing manganese oxide as a positive electrode was produced, and a charge / discharge cycle test was performed. It was found that no potential flat portion was observed around 4.5 V during charging, and no oxygen was released. The cycle in which the maximum discharge capacity was obtained was the 11th cycle, and the maximum discharge capacity value was 277 mAh / g. The value of Y calculated from this discharge capacity value of 277 mAh / g is 0.88, which is Li _0.32 M _0.80 O ₂ (Li _0.32 Mn _0.61 Ni _0.19 O ₂ ). It was. The X-ray diffraction pattern after repeating the charge / discharge cycle belonged to the same monoclinic crystal structure as that of the lithium-containing manganese oxide.

Example 2
2.00 g of oxyhydroxide containing Mn and Ni obtained in Production Example and 1.39 g of commercially available lithium carbonate (made by Rare Metallics) were dry-mixed for 15 minutes using a mortar, and then ethanol (reagent) 2 mL of special grade, manufactured by Kishida Chemical Co., Ltd. was added and mixed for 60 minutes. 1.00 g of the obtained mixed powder was put in a baking dish, subjected to heat treatment at 900 ° C. for 12 hours in a box furnace, cooled to room temperature, and a sample was taken out. The temperature increase rate and temperature decrease rate were 300 ° C./hr. When the temperature was lowered, the furnace was cooled at 300 ° C. or lower.

From the evaluation of crystallinity and composition analysis of the prepared sample, the obtained lithium-containing manganese oxide belongs to monoclinic crystals, the Ni / Mn molar ratio is 0.333, and the Li / (Mn + Ni) molar ratio is 1.63. Met. From this value, it was confirmed that X was 0.09, and a lithium-containing manganese oxide of Li _1.24 M _0.76 O ₂ (Li _1.24 Mn _0.57 Ni _0.19 O ₂ ) was obtained. I understood. The lithium-containing manganese oxide had a BET specific surface area of 0.2 m ² / g and a primary particle size of 1 μm.

A coin cell using the obtained lithium-containing manganese oxide as a positive electrode was produced, and a charge / discharge cycle test was performed. It was found that no potential flat portion was observed around 4.5 V during charging, and no oxygen was released. The cycle in which the maximum discharge capacity was obtained was the 25th cycle, and the maximum discharge capacity value was 250 mAh / g. The value of Y calculated from this discharge capacity value 250 mAh / g was 0.62, and was Li _0.62 M _0.76 O ₂ (Li _0.62 Mn _0.57 Ni _0.19 O ₂ ). . The powder X-ray diffraction pattern of this lithium-containing manganese oxide is shown in FIG.

When the powder X-ray diffraction pattern measurement was performed in the discharge state after repeated 25 cycles of charging / discharging, the appearance of a new diffraction peak was observed in addition to the original diffraction pattern, and two phases with different lattice constants were included It was a thing. The above new diffraction peak is also attributed to the monoclinic crystal, and the manganese oxide obtained by repeating the charge / discharge cycle maintains the same monoclinic crystal structure as the lithium-containing manganese oxide. I understood.

Example 3
A lithium-containing manganese oxide was prepared in the same manner as in Example 2 except that 1.43 g of lithium carbonate was used.
From the evaluation of crystallinity and composition analysis of the prepared sample, it was attributed to monoclinic crystal, the Ni / Mn molar ratio was 0.315, and the Li / (Mn + Ni) molar ratio was 1.67. It was. From these values, it was found that X was 0.08, and it was a lithium-containing manganese oxide of Li _1.25 M _0.75 O ₂ (Li _1.25 Mn _0.57 Ni _0.18 O ₂ ). It was. The lithium-containing manganese oxide had a BET specific surface area of 0.2 m ² / g and a primary particle size of 1 μm. The powder X-ray diffraction pattern of this lithium-containing manganese oxide is shown in FIG.

A coin cell using the obtained lithium-containing manganese oxide as a positive electrode was produced, and a charge / discharge cycle test was performed. It was found that no potential flat portion was observed around 4.5 V during charging, and no oxygen was released. The cycle in which the maximum discharge capacity was obtained was the 25th cycle, and the maximum discharge capacity value was 270 mAh / g. The value of Y calculated from this discharge capacity value 270 mAh / g was 0.66 and was Li _0.59 Mn _0.75 O ₂ (Li _0.59 Mn _0.57 Ni _0.18 O ₂ ). . The X-ray diffraction pattern after repeating the charge / discharge cycle belonged to the same monoclinic crystal structure as that of the lithium-containing manganese oxide.
In addition, the powder X-ray-diffraction pattern of the manganese oxide in the discharge state after repeating charge / discharge cycle 25 times was shown in FIG. Further, FIG. 4 shows a charge / discharge profile after the charge / discharge cycle is repeated 25 times.

Example 4
A lithium-containing manganese oxide was prepared in the same manner as in Example 2 except that 1.47 g of lithium carbonate was used.
From the evaluation of crystallinity and composition analysis of the prepared samples, the obtained crystals belonged to monoclinic crystals, and the Ni / Mn molar ratio was 0.321 and the Li / (Mn + Ni) molar ratio was 1.70. From these values, it was found that X was 0.07, and it was a lithium-containing manganese oxide of Li _1.26 Mn _0.74 O ₂ (Li _1.26 Mn _0.56 Ni _0.18 O ₂ ). It was. The lithium-containing manganese oxide had a BET specific surface area of 0.1 m ² / g and a primary particle size of 1 μm. The powder X-ray diffraction pattern of this lithium-containing manganese oxide is shown in FIG.

A coin cell using the obtained lithium-containing manganese oxide as a positive electrode was produced, and a charge / discharge cycle test was performed. It was found that no potential flat portion was observed around 4.5 V during charging, and no oxygen was released. The cycle in which the maximum discharge capacity was obtained was the 25th cycle, and the maximum discharge capacity value was 250 mAh / g. The value of Y calculated from this discharge capacity ratio value of 250 mAh / g is 0.61 and is Li _0.65 M _0.74 O ₂ (Li _0.65 Mn _0.56 Ni _0.18 O ₂ ). It was. The X-ray diffraction pattern after repeating the charge / discharge cycle belonged to the same monoclinic crystal structure as that of the lithium-containing manganese oxide.

Example 5
A coin cell using a lithium-containing manganese oxide synthesized in the same manner as in Example 2 as a positive electrode was prepared, and a charge / discharge cycle test was performed. It was found that no potential flat portion was observed around 4.5 V during charging, and no oxygen was released. The cycle in which the maximum discharge capacity was obtained was the 25th cycle, and the maximum discharge capacity value was 250 mAh / g. The value of Y calculated from this discharge capacity value 250 mAh / g was 0.62, and was Li _0.62 M _0.76 O ₂ (Li _0.62 Mn _0.57 Ni _0.19 O ₂ ). .
When the powder X-ray diffraction pattern measurement was performed in the discharge state after repeating 50 cycles of charge / discharge, it was found that the crystal structure was a manganese oxide belonging to a monoclinic crystal.

Example 6
A coin cell using the lithium-containing manganese oxide obtained in Example 1 as a positive electrode was prepared, a charge / discharge cycle test was performed, and a manganese oxide in a discharged state after repeating the charge / discharge cycle 20 times was obtained. It was.
FIG. 6 shows the synchrotron radiation X-ray measurement result and Rietveld analysis result of the manganese oxide in the discharge state after repeating the charge / discharge cycle 20 times. As a result of the crystal structure analysis, fitting is possible with two monoclinic phases (monoclinic crystal 1 and monoclinic crystal 2), and R values indicating the accuracy of the analysis are Rp = 2.06%, wRp = 3. Since it converged to 20%, high-precision analysis was possible. The existence ratio of the two phases was determined to be 41% and 59%.

The lattice parameters of monoclinic crystal 1 are as follows: a = 5.0262 (6) Å, b = 8.7006 (10), c = 5.1009 (4) Å, β = 108.844 (9) °, V = 211.11 (4) Å ³ , Z = 4. The lattice parameters of the monoclinic crystal 2 are as follows: a = 5.00096 (3) Å, b = 8.6936 (6), c = 5.0600 (2) Å, β = 109.128 (5) °, V = It was 208.20 (2) ^{３ 3} and Z = 4.
In order to judge the validity of the crystal structure analysis result, the interatomic distance was obtained from the Rietveld analysis result.

As a result of the analysis of the monoclinic crystal 1, the interatomic distance from the six oxygen atoms around the four kinds of metal seats is 1.92 (9) Å to 2.05 (5) Å for the M1 seat, and 2 for the M2 seat. .06 (5) Å-2.13 (9) Å, M3 seats are 2.08 (3) Å-2.22 (6) Å, M4 seats are 2.00 (1) Å-2.04 (0 ) In the meantime, since the interatomic distance showed a significant variation beyond the error range, it was found that the monoclinic system is appropriate.
As a result of the analysis of the monoclinic crystal 2, the interatomic distance from the six oxygen atoms around the four metal seats is 1.85 (6) Å to 1.89 (3) Å for the M1 seat and 2 for the M2 seat. .12 (1) Å-2.24 (8) Å, M3 seats are 1.83 (0) Å-2.43 (9) Å, M4 seats are 2.00 (6) Å-2.10 (5) ) In the meantime, since the interatomic distance showed a significant variation beyond the error range, it was found that the monoclinic system is appropriate.

Example 7
A coin cell using the lithium-containing manganese oxide obtained in Example 1 as a positive electrode was prepared, a charge / discharge cycle test was performed, and a manganese oxide in a discharged state after repeating the charge / discharge cycle 30 times was obtained. It was.
FIG. 7 shows the synchrotron radiation X-ray measurement result and Rietveld analysis result of the manganese oxide in the discharge state after repeating the charge / discharge cycle 30 times. As a result of the crystal structure analysis, fitting is possible with two monoclinic phases (monoclinic crystal 1 and monoclinic crystal 2), and R values indicating the accuracy of analysis are Rp = 2.20%, wRp = 3. Since it converged to 21%, high-precision analysis was possible. From this result, it was found that the crystal structure was a manganese oxide belonging to two monoclinic crystals. Further, the abundance ratios of the two phases were determined to be 41% and 59%, and it was found that the abundance ratios of the two monoclinic crystals were not different from the discharge state after 20 charge / discharge cycles were repeated.
The lattice parameters of monoclinic crystal 1 are as follows: a = 5.0149 (6) Å, b = 8.7117 (9), c = 5.1064 (3) Å, β = 108.996 (8) °, V = 210.94 (4) ^{３ 3} , Z = 4. The lattice parameters of the monoclinic crystal 2 are as follows: a = 5.0146 (4) Å, b = 8.6683 (7), c = 5.0641 (2) Å, β = 109.041 (5) °, V = It was 208.56 (2) ^{３ 3} and Z = 4.

In order to judge the validity of the crystal structure analysis result, the interatomic distance was obtained from the Rietveld analysis result.
As a result of the analysis of the monoclinic crystal 1, the distance between the six oxygen atoms around the four metal seats is 1.98 (1) Å to 1.98 (9) Å for the M1 seat and 2 for the M2 seat. .11 (2) Å-2.14 (0) Å, M3 seats are 1.95 (3) Å-2.34 (0) Å, M4 seats are 2.00 (1) Å-2.08 (5) ) In the meantime, since the interatomic distance showed a significant variation beyond the error range, it was found that the monoclinic system is appropriate.
As a result of the analysis of the monoclinic crystal 2, the interatomic distance from the six oxygen atoms around the four metal seats is 1.85 (6) Å to 1.89 (3) Å for the M1 seat and 2 for the M2 seat. .12 (1) Å-2.24 (8) Å, M3 seats are 1.83 (0) Å-2.43 (9) Å, M4 seats are 2.00 (6) Å-2.10 (5) ) On the other hand, the interatomic distances at each site showed significant variation beyond the error range, indicating that the monoclinic system was appropriate.

Reference Example The same procedure as in Examples 1 to 5 was performed except that a commercially available NCM (EQ-lib-LNCM-111, manufactured by MTI JAPAN) was used instead of the lithium-containing manganese oxide obtained in each Example. A coin cell was manufactured, and a charge / discharge cycle test was repeated at room temperature (22-27 ° C.) with a constant current of 10 mA / g and a battery voltage between 2.0 V and 3.3 V. .
The X-ray diffraction pattern of the NCM is a hexagonal crystal and has a crystal structure different from that of the above example. The cell using the positive electrode of NCM showed the maximum discharge capacity in the first cycle, and the value was 150 mAh / g which was considerably smaller than the manganese oxide of the above example. FIG. 4 shows a charge / discharge profile after 25 cycles of the charge / discharge cycle.

The manganese oxide of the present invention can be used in various fields including positive electrode materials for lithium secondary batteries.
It should be noted that the entire content of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2017-72111 filed on March 31, 2017 is cited here as the disclosure of the specification of the present invention. Incorporate.

Claims (10)

1. General formula Li _{(4 / 3−XY)} M _{(2/3 + X)} O ₂ (where 0 ≦ X ≦ 1/3, 0 <Y ≦ 4/3, M is only Mn and Ni, 0 <Ni / Mn molar ratio ≦ 2/5 is satisfied.] And the crystal structure belongs to a monoclinic crystal (space group C2 / m).
2. 2. The general formula according to claim 1, wherein 1/20 ≦ X ≦ 1/8, 0.7 ≦ Y ≦ 1.0, and 0 <Ni / Mn molar ratio ≦ 1/3. Manganese oxide.
3. The manganese oxide according to claim 1 or 2, comprising two phases having different lattice constants.
4. The method for producing a manganese oxide according to any one of claims 1 to 3, wherein the general formula Li _{(4 / 3-X)} M _{(2/3 + X)} O ₂ (where 0 ≦ X ≦ 1) / 3, M is only Mn and Ni, or Mn, Ni and Mn, and 0 <Ni / Mn molar ratio ≦ 2/5.), And the BET surface area is 0.5 m ² / g or less. The production is characterized in that the lithium-containing manganese oxide having a primary particle size of 0.5 μm or more and a crystal structure belonging to a monoclinic crystal (space group C2 / m) is obtained by electrochemical oxidation / reduction. Method.
5. In the above general formula, the production method according to claim 4, wherein 1/20 ≦ X ≦ 1/8 and 0 <Ni / Mn molar ratio ≦ 1/3 is satisfied.
6. 6. The production method according to claim 4, wherein the lithium-containing manganese oxide has a BET specific surface area of 0.1 to 0.4 m ² / g.
7. The production method according to any one of claims 4 to 6, wherein the primary particle diameter of the lithium-containing manganese oxide is 0.5 to 1.0 µm.
8. The method according to any one of claims 4 to 7, wherein the electrochemical oxidation / reduction is performed through charging / discharging in a lithium battery using a positive electrode using the lithium-containing manganese oxide.
9. The manufacturing method according to claim 6, wherein a lithium battery using a positive electrode using the lithium-containing manganese oxide can be used as it is as a lithium secondary battery.
10. A lithium secondary battery comprising a positive electrode containing the manganese oxide according to any one of claims 1 to 3.

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