JP2001048545A - Production of lithium-manganese multiple oxide and secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject multiple oxide maintaining its performance as an anode active substance without the need of reaction at high temperatures for a long time even through reaction at relatively low temperatures for a short time by reaction between a lithium compound and a manganese compound in the presence of a boron compound in a liquid state. SOLUTION: This lithium manganese multiple oxide is obtained by reaction between a lithium compound (e.g. lithium hydroxide) and a manganese compound (e.g. MnO2) in the presence of a boron compound (e.g. H3BO3) in a liquid state; wherein the molar ratio Li/Mn is pref. about 0.8-1.2 when this multiple oxide is of lamellar structure, or about 0.4-0.6 in the case of spinel structure, and the molar ratio B/Mn is pref. 0.001-0.05; the reaction is carried out in the presence of a compound containing a metallic element as substituent dope (AlOOH or the like with a particle size of about <=10 μm) at 500-900 deg.C for 1-100 h.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a lithium manganese composite oxide and a secondary battery using the same as a positive electrode active material.

[0002]

2. Description of the Related Art A lithium ion secondary battery, which functions as a battery by a positive electrode and a negative electrode absorbing and releasing lithium ions from each other, has a high voltage and a high energy density, and is used for mobile phones, portable personal computers, video cameras, It can be suitably used for applications such as electric vehicles. As a positive electrode active material for a lithium ion secondary battery, a layered composite oxide, Li _{1- x} CoO ₂ (0 ≦ x ≦ 1), can obtain a high voltage of 4V class and has a high energy density From that
It is already widely used. On the other hand, Co, a raw material, is scarce in terms of resources and expensive, so considering the possibility that demand will continue to expand significantly, there is concern about the supply of raw materials and the price may rise further. It is possible. Therefore,
Li _1-x CoO ₂ instead obtained positive electrode active material as an inexpensive Mn of Li _1-x MnO ₂ is layered composite oxide raw material (0 ≦ x ≦ 1) and spinel-type Mn-based composite oxide Li _{1- x} Mn ₂ O ₄ (0 ≦ x ≦ 1)
It has been considered to use as a positive electrode active material. However, these lithium manganese composite oxides have 50
There is a problem in that the capacity deterioration when repeatedly charged and discharged at a temperature of 6060 ° C. is greater than that of the above-mentioned Li _1-x CoO ₂ .
In this regard, in order to (1) improve the crystallinity of the lithium-manganese composite oxide, and (2) stabilize the crystal structure, a part of Mn is replaced by one or more elements to increase the capacity. It has been clarified that there is a deterioration suppressing effect.

As a method for producing a lithium manganese composite oxide, a method of reacting a lithium compound and a manganese compound at a high temperature is usually used. However, in order to produce a lithium manganese composite oxide having good crystallinity, a long-time reaction at a high temperature is required, and there is a problem that the production cost is increased. Further, when the reaction temperature is further increased for the purpose of shortening the reaction time, there is a problem that the performance as a positive electrode active material is reduced due to decomposition of the lithium manganese composite oxide. As a method of solving this problem, a method of firing a lithium compound and a manganese compound in the presence of an inert melting agent (Japanese Patent Laid-Open No. 10-3245)
No. 21) has been proposed.

However, potassium, barium, and potassium, which are exemplified as inert fluxes in the above-mentioned improvement method,
Lithium halides, sulfates and molybdates do not always have a sufficient effect as a melting agent, and need to be added in large amounts to the lithium-manganese composite oxide to be produced. As a result, a large amount of the inert flux that does not function as a positive electrode active material must be removed by washing after baking, and furthermore, filtration and drying are required, which is not preferable in terms of production cost.

[0005]

(1) The performance as a positive electrode active material (discharge capacity, discharge capacity at high temperature) even without reaction for a long time at low temperature (3) The addition amount of the inert flux is small with respect to the lithium manganese composite oxide to be produced, and as a result, a large amount that does not function as a positive electrode active material is obtained. There is a need for a method for producing a lithium manganese composite oxide, which is preferable in terms of production cost since it is not necessary to remove the inert flux by rinsing with water after calcination, and furthermore, there is no filtration or drying.

[0006]

Means for Solving the Problems As a result of extensive studies, the present inventors have found that a lithium compound and a manganese compound are reacted in the presence of a boron compound in a liquid phase, which is one of inert fluxes. The inventors have found that the above problems can be solved, and have completed the present invention. That is, the gist of the present invention resides in a method for producing a lithium-manganese composite oxide, which comprises reacting a lithium compound with a manganese compound in the presence of a boron compound in a liquid phase.

[0007] In a preferred embodiment of the present invention, the above-mentioned reaction is carried out in the presence of a compound containing a metal element to be a substitution dope; The above production method, wherein the amount of the boron compound in the liquid phase is an amount such that the molar ratio of B / Mn to the amount of the manganese compound is 0.001 to 0.05. The above-mentioned production method, which is characterized in that the reaction temperature is 900 ° C. or lower. Another embodiment of the present invention is a secondary battery using the lithium manganese composite oxide manufactured by the above manufacturing method as a positive electrode active material.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Lithium manganese in the present invention
Complex oxides include those having a layered structure and those having a spinel type.
No. Some of the manganese has been replaced by lithium
If some of lithium and / or manganese are other metals
It may be replaced by an element. E used in the present invention
Iodine compounds react lithium compounds with manganese compounds
A compound that produces a liquid phase at the temperature
If Li_TwoB_FourO₇, Li_TwoB_TwoO_Four, Li₆B _FourO₇Lithium borate etc.
, Na_TwoB₆O_Ten, Na_TwoB_FourO₇Sodium borate, such as K_TwoB_TenO
₁₆, K_TwoB_FourO₇Potassium borate, B etc._TwoO_Three, H_ThreeBO_ThreeSelect from etc.
One or more mixtures and decomposed products thereof
You can name an adult. Especially B_TwoO_Three, H_ThreeBO_ThreeOr e
Lithium borate is preferred. Amount of boron compound used
Is usually a molar ratio of B / Mn to the amount of manganese compound
0.001 or more, preferably 0.005 or more, more preferably
Or 0.01 or more, and usually 0.05
Or less, preferably 0.04 or less, more preferably 0.04 or less.
The amount is 3 or less. If the molar ratio of B / Mn is too small,
It may not be possible to obtain a sufficient discharge capacity maintenance rate, and it is too large
If so, a sufficient discharge capacity may not be obtained.

The lithium compound used in the present invention includes:
For example, one or a mixture of two or more selected from lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxide and the like and hydrates thereof can be mentioned. As the manganese compound used in the present invention, for example, MnO ₂ , Mn
Manganese oxides such as ₂ O ₃ , Mn ₃ O ₄ , MnO, or MnCO
₃ or the like, or one or a mixture of two or more kinds selected from MnOOH and the like. When a lithium compound and a manganese compound are reacted, the Li / Mn ratio is preferably from 0.8 to 1.2, more preferably from 0.9 to 1.2 in terms of molar ratio when a lithium manganese composite oxide having a layered structure is synthesized.
１．２1.2. When synthesizing a lithium manganese composite oxide having a spinel structure, the molar ratio is preferably from 0.4 to 0.6, and more preferably from 0.45 to 0.55. At the time of the reaction, the amounts of the lithium compound and the manganese compound may be adjusted so that the ratio of Li and Mn falls within the range of the above molar ratio. In the case of producing a lithium manganese composite oxide in which lithium or manganese is partially substituted by another metal element with another element in order to stabilize the crystal structure of the produced lithium manganese composite oxide, It is sufficient to reduce the amounts of Li and Mn corresponding to.

As a metal element that partially replaces Li or Mn, that is, a metal element that becomes a substitution dope, Al, Fe, Ga, Bi, Sn,
V, Cr, Co, Cu, Zn, Mg, Ti, Ge, Nb, Ta, Li, etc.
Preferred are Al, Fe, Ga, Cr, Co, Mg, and Ti, and particularly preferred is Al. In order to obtain a lithium-manganese composite oxide in which part of lithium or manganese has been replaced by another metal element, when reacting a lithium compound with a manganese compound in the presence of a boron compound in a liquid phase, these metal elements are used. The compound may be reacted. Depending on the selection of the two metal elements, when a lithium compound and a manganese compound are reacted in the presence of a boron compound in a liquid phase, a part of lithium and manganese are respectively reacted by reacting a compound containing the two metal elements. A lithium manganese composite oxide substituted by one different metal element can be obtained.

As the compounds containing a metal element, these compounds
Metal oxides, hydroxides, organic acid salts, chlorides, nitrates,
Sulfates and the like and hydrates thereof are exemplified. In particular
Al_TwoO _Three, AlOOH, Al (OH)_Three, Al (CH_ThreeCOO)_Three, AlCl_Three, Al
(NO_Three)_Three・ 9H_TwoO, Al_Two(SO_Four)_ThreeAnd the like, preferably Al
_TwoO_Three, AlOOH, Al (OH)_ThreeIt is. Lithium compound and man
Before reacting in the presence of a boron compound,
It is preferable to mix them in advance. Lithium and / or lithium
Lithium in which part of the metal has been replaced by another metal element
When obtaining manganese composite oxide, it becomes substitution dope
Compounds containing metal elements also react in the presence of boron compounds.
Before mixing with lithium and manganese compounds.
It is preferable to combine them. Does not melt at reaction temperature
In the case of compounds, use pulverization or other means to increase reactivity
More preferably, the particle diameter is set to 10 μm or less.
There are no particular restrictions on the order of grinding and mixing, and
Can be crushed and mixed. Grinding and mixing methods are dry
Or wet type, such as ball mill, vibratory mill, beads
Examples include a method using a device such as a mill. Wet mixing
If the mixture has been dried, remove the
Granulation may be performed, for example, to 1 to 100 μm by a step.

The temperature at which the boron compound and the manganese compound are reacted in the presence of the boron compound in the liquid phase is usually 5
00 ° C or higher, preferably 550 ° C or higher.
The temperature is preferably 000 ° C or less, particularly 900 ° C or less. If the temperature is too low, a long reaction time is required to obtain a lithium-manganese composite oxide having good crystallinity, which is not preferable. On the other hand, if the temperature is too high, a phase other than the desired layered or spinel-type lithium manganese composite oxide is generated, or a lithium manganese composite oxide having many defects is generated. It is not preferable because the capacity is reduced or the crystal structure is deteriorated due to charge and discharge. When the temperature is raised from room temperature to the above reaction temperature, for example, 5 ° C./min.
It is preferable that the temperature is gradually increased at the following temperature or that the temperature is temporarily stopped halfway and a holding time at a constant temperature is provided.

The reaction time at the reaction temperature is usually from 1 hour to 100 hours. If the reaction time is too short, a lithium-manganese composite oxide having good crystallinity cannot be obtained, and an excessively long reaction time is not practical. In order to obtain a lithium manganese composite oxide having few crystal defects, after the above reaction,
It is preferable to slowly cool to room temperature.
° C / min. It is preferable to gradually cool to room temperature at the following cooling rate. The above reaction is preferably performed in a vacuum or in an inert atmosphere such as nitrogen or argon when producing a layered lithium manganese composite oxide, and in the air when producing a spinel type lithium manganese composite oxide. Alternatively, the treatment is preferably performed in an oxygen-containing atmosphere such as oxygen. The heating apparatus used for this reaction is not particularly limited as long as the above-mentioned temperature and atmosphere can be achieved, and for example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln and the like can be used.

The lithium manganese oxide produced by the above reaction is composed of secondary particles having a particle diameter of 1 to 100 μm in which primary particles having a particle diameter of 0.1 to 3 μm are aggregated, and having a specific surface area of 0 to 0 due to nitrogen adsorption. It is preferably from 1 to 5 m ² / g. The size of the primary particles can be controlled by the reaction temperature, time, and amount of the boron compound. Increasing at least one of the reaction time, time, and the amount of the boron compound increases the particle size of the primary particles. 2
The particle size of the secondary particles can be controlled by pulverization or granulation before the reaction, pulverization after the reaction, classification, and the like. The specific surface area can be controlled by the particle size of the primary particles and the particle size of the secondary particles, and is reduced by increasing the particle size of the primary particles and / or the particle size of the secondary particles.

After the lithium manganese composite oxide produced by the production method of the present invention is reacted in an aqueous solution, molten salt or vapor of a compound containing a substitution metal element, the substitution element is optionally subjected to lithium manganese composite oxidation. Heat treatment is performed again to diffuse Li
A part of Mn may be replaced by a metal element to be a substitution dope. Not only the unsubstituted lithium-manganese composite oxide obtained by the production method of the present invention, but also a lithium-manganese composite oxide in which Li or Mn is partially substituted, unsubstituted Li or Mn is obtained by the above-described method. Further substitution may be made. Using the thus obtained lithium manganese oxide as a positive electrode active material, a secondary battery can be manufactured. As an example of the secondary battery of the present invention, a secondary battery including a positive electrode, a negative electrode, an electrolytic solution, and a separator may be mentioned. An electrolyte exists between the positive electrode and the negative electrode, and the separator does not contact the positive electrode and the negative electrode. So be placed between them.

As the positive electrode, the lithium manganese oxide (positive electrode active material) obtained in the present invention, a conductive material, a binder, and a solvent for uniformly dispersing the same are mixed in a fixed amount, and then the current is collected. Apply on the body. As the conductive material used here, natural graphite, artificial graphite, acetylene black, etc., as the binder polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, etc., dispersed Solvents include N-methylpyrrolidone, tetrahydrofuran, dimethylformamide and the like, but are not limited thereto. Examples of the material of the current collector include aluminum and stainless steel. After being coated on the current collector, it is dried and usually consolidated by a roller press or other methods. On the other hand, as the negative electrode, a material obtained by applying a carbon-based material (natural graphite, pyrolytic carbon, or the like) on a current collector such as Cu, a lithium metal foil, a lithium-aluminum alloy, or the like can be used.

The electrolytic solution used in the present invention is a non-aqueous electrolytic solution. Specifically, as the electrolytic salt, LiClO ₄ , LiAsF ₆ , LiPF
₆ , LiBF ₄ , LiBr, LiCF ₃ SO ₃ and the like.Examples of the solvent constituting the electrolyte include tetrahydrofuran, 1,4-dioxane, dimethylformamide, acetonitrile, benzonitrile, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate. , Ethylene carbonate, propylene carbonate, butylene carbonate, and the like, but are not limited thereto. These solvents may be used alone or as a mixture of two or more. Examples of the separator used in the present invention include a polymer such as Teflon, polyethylene, polypropylene, and polyester, a nonwoven fabric filter such as glass fiber, and a composite nonwoven fabric filter of glass fiber and polymer fiber. In this way, a secondary battery was prepared using the positive electrode active material obtained in the present invention, and when the battery performance was evaluated, the charge / discharge capacity per unit weight was large, and the capacity after a charge / discharge cycle at a high temperature. It has been found that a secondary battery having a high maintenance rate can be obtained. Hereinafter, the present invention will be described in more detail with reference to Examples.

[0018]

EXAMPLE 1 LiOH.H ₂ O, Mn ₂ O ₃ and AlOOH were weighed such that the molar ratio of Li: Mn: Al was 1.04: 1.88: 0.12.
To 100 parts by weight of the raw material powder, 180 parts by weight of pure water and 2 parts by weight of an ammonium polycarboxylate-based dispersant were added, and then mixed and pulverized by a bead mill to obtain a solid matter having an average particle size of 0.5 μm. A slurry was obtained. A part of this slurry was fractionated, and H ₃ BO ₃ was added and dissolved so that the molar ratio of B / Mn was 0.0106. This slurry was spray-dried, and calcined in the air at 750 ° C. for 5 hours in a box furnace to obtain substantially spherical particles having an average particle diameter (secondary particle diameter) of 15 μm. Was.

As a result of measuring the powder X-ray diffraction pattern of the particles, it was confirmed that the particles were a lithium manganese composite oxide having a spinel structure. As a result of observation with a scanning electron microscope, the particle diameter of the primary particles was about 0.6 μm. Further, as a result of measuring the specific surface area by nitrogen adsorption, the specific surface area was 0.9 m ² / g. 75 parts by weight of the thus obtained lithium manganese composite oxide, 20 parts by weight of acetylene black as a conductive material, and 5 parts by weight of polytetrafluoroethylene as a binder were mixed and molded to prepare a positive electrode pellet. . Using this positive electrode pellet, a coin-type battery was produced. For the negative electrode material, lithium metal, and for the electrolyte,
3: 7 of ethylene carbonate and diethyl carbonate
1 mol / l lithium hexafluorophosphate (LiPF
₆ ) was used. Using this battery,
The discharge capacity per unit weight of the positive electrode material when charged and discharged at a current density of 1 mA / cm ² at 5 ° C. was 115 mAh /
g. A coin-shaped battery was prepared in the same manner as above except that carbon was used as the negative electrode material.
The capacity retention after 100 cycles when charging / discharging at a current density of mA / cm ² was 72% with respect to the first cycle.

Comparative Example 1 The slurry prepared in Example 1 was spray-dried without adding H ₃ BO _3, and calcined at 900 ° C. for 5 hours in the air to obtain an average particle size (particle size of secondary particles). 15 μm, roughly spherical granulated particles were obtained. As a result of measuring the powder X-ray diffraction pattern of the particles, it was confirmed that the particles were a lithium manganese composite oxide having a spinel structure. The particle diameter of the primary particles determined by observation with a scanning electron microscope was about 0.4 μm. The specific surface area by nitrogen adsorption was 1.9 m ² / g.

A positive electrode pellet was prepared in the same manner as in Example 1,
Using lithium metal for the negative electrode material, make a coin-type battery,
When the discharge capacity per unit weight of the positive electrode material was measured at 25 ° C. at a current density of 1 mA / cm ² , the discharge capacity was 113 mA.
h / g. A coin-type battery was prepared in the same manner as above except that carbon was used as the negative electrode material, and 1 mA / c at 50 ° C.
The capacity retention after 100 cycles when charging and discharging at a current density of m ² was 70% with respect to the first cycle.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

According to the present invention, (1) the performance as a positive electrode active material (discharge capacity, discharge capacity at high temperature) can be achieved even at a low temperature for a short time without requiring a long reaction at a high temperature. (3) The addition amount of the inert flux is small with respect to the lithium manganese composite oxide to be produced, and as a result, a large amount that does not function as a positive electrode active material is obtained. There is provided a method for producing a lithium manganese composite oxide, which is preferable in terms of production cost because it is not necessary to remove the inert flux by rinsing with water after calcination, and furthermore, there is no filtration or drying.

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Claims (6)

[Claims] 1. A method for producing a lithium-manganese composite oxide, comprising reacting a lithium compound with a manganese compound in the presence of a boron compound in a liquid phase. 2. The method according to claim 1, wherein the reaction is performed in the presence of a compound containing a metal element to be a substitution dope.
The manufacturing method as described. 3. The method according to claim 2, wherein the metal element serving as the substitution dope is an aluminum compound. 4. The amount of the boron compound in the liquid phase is preferably in the range of 0.001 to 0.1 mol / mol of the manganese compound.
The amount is 0.05.
The method according to any one of the above. 5. The method according to claim 1, wherein the reaction is performed at 500 to 900 ° C. 6. A secondary battery using the lithium manganese composite oxide produced by the production method according to claim 1 as a positive electrode active material.