JP5482755B2 - Novel lithium manganese composite oxide, method for producing the same, and use thereof - Google Patents

Description

The present invention relates to a novel lithium manganese oxide, particularly, formula _{Li 1 + X Mn 2-Y} -Z M Z O 4 + δ (M in the formula Ni, Co, Fe, Cr, Cu, B, Al , Ga and In, at least one element selected from 0 ≦ X ≦ 1/3, 0 ≦ Y ≦ 1/3, 0 <Z ≦ 0.25, −0.14 ≦ δ ≦ 0.5 Lithium manganese having a spinel crystal structure with an average particle size of 5 to 20 μm, a BET specific surface area of 0.6 m ² · g ⁻¹ or less, and an average crystallite size of 1000 angstroms or more determined by the method of Hall The present invention relates to a composite oxide, a manufacturing method thereof, and a lithium secondary battery using the lithium manganese oxide as a positive electrode active material.

  Manganese-based materials are one of the promising materials for various applications because they are inexpensive, have abundant resources of manganese as a raw material, and are environmentally friendly.

  Lithium secondary batteries are theoretically capable of constructing batteries with high energy density, so they are being applied to a wide range of fields as new secondary batteries that will lead the next generation. Researches aimed at high performance are being promoted.

  With the spread of personal use mobile devices, the development of small, lightweight, high energy density lithium secondary batteries has become strongly desired, and lithium ions using carbonaceous materials that can store and release lithium in the negative electrode. The battery was put into practical use.

Lithium cobalt oxide (hereinafter referred to as LiCoO ₂ ) is mainly used as the positive electrode material of current lithium ion batteries, but the development of alternative materials is desired because the cobalt raw material is expensive.

Examples of the positive electrode material showing a 4V class electromotive force in place of LiCoO ₂ include lithium nickel oxide (hereinafter referred to as LiNiO ₂ ) and lithium manganese spinel (hereinafter referred to as LiMn ₂ O ₄ ). LiMn is suitable for use as an auxiliary power source for batteries and fuel cells for hybrid electric vehicles because it is inexpensive, has a small impact on the environment, and is easy to ensure safety when using batteries. ₂ O ₄ is considered to be the most excellent positive electrode material, and application studies have been intensively promoted, and some have already been put into practical use.

In hybrid type electric vehicle batteries, power assist performance when starting and accelerating the vehicle and regenerative performance of kinetic energy during deceleration are important. Discharge characteristics) are required. To meet such demands, measures have been taken so far by optimizing the battery structure and electrode structure, but improvement of the positive electrode material itself is important for further improvement of battery performance. Moreover, since the high temperature stability of LiMn ₂ O ₄ is inferior to that of LiCoO ₂ or LiNiO ₂ , improvement of this point is also important.

  The object of the present invention is to propose a novel lithium manganese oxide having excellent high-rate charge / discharge characteristics and high-temperature stability and a method for producing the same, and further, a high-power lithium secondary material using this compound as a positive electrode active material. To provide a battery.

As a result of intensive studies aimed at simultaneously improving the high-rate charge / discharge characteristics and high-temperature stability of LiMn ₂ O ₄ , a manganese compound having an average oxidation number of manganese of 8/3 or more, a lithium compound, Ni, Co , Fe, Cr, Cu, B, Al, Ga, In, a mixture of at least one metal material selected from metal materials is calcined by a predetermined method, so that the general formula Li _{1 + X} Mn _2-YZ M _Z O _{4 + δ} (wherein M is at least one selected from Ni, Co, Fe, Cr, Cu, B, Al, Ga and In, and 0 ≦ X ≦ 1/3, 0 ≦ Y ≦ 1/3, 0 <Z ≦ 0.25, −0.14 ≦ δ ≦ 0.5), an average particle diameter of 5 to 20 μm, a BET specific surface area of 0.6 m ² · g ⁻¹ or less, and determined from the method of Hall. Average crystallite diameter of 1000 angstroms or more A novel spinel crystal structure lithium manganese composite oxide of 1400 angstroms or less can be synthesized. Furthermore, by using this as a positive electrode active material for lithium secondary batteries, it combines high-rate charge / discharge characteristics and high-temperature stability. The present inventors have found that a manganese-based lithium secondary battery can be constructed, and have completed the present invention.

  Hereinafter, the present invention will be specifically described.

Formula _{Li 1 + X Mn 2-Y} -Z M Z O 4 + δ ( wherein M is at least one element selected Ni, Co, Fe, Cr, Cu, B, Al, Ga, from an In, 0 ≦ X ≦ 1/3, 0 ≦ Y ≦ 1/3, 0 <Z ≦ 0.25, −0.14 ≦ δ ≦ 0.5), and an oxide having a spinel crystal structure. The compound of the present invention is composed of lithium, manganese, metal element M (where M is at least one element selected from Ni, Co, Fe, Cr, Cu, B, Al, Ga, and In), and oxygen. The lithium is occupied by the 8a site at the tetrahedron position and the manganese and the metal element M, or lithium and manganese, and the metal element M are occupied at the 16d site at the octahedron position in the cubically packed oxygen array. If the occupation ratio of each site of lithium, manganese, and metal element M is within the range of the above general formula, an oxide having a spinel crystal structure is obtained.

  It is important that the lithium manganese oxide of the present invention contains at least one element selected from Ni, Co, Fe, Cr, Cu, B, Al, Ga and In in addition to each element of lithium, manganese and oxygen. It is. By containing these elements, stability at high temperatures is improved.

  The lithium manganese oxide of the present invention must have an average particle diameter of 5 to 20 μm. When the average particle diameter is less than 5 μm, the decrease in high-temperature stability becomes remarkable, and in addition, the workability at the time of producing an electrode is unfavorable. In addition, when it exceeds 20 μm, the high-rate charge / discharge characteristics are remarkably deteriorated.

The lithium manganese oxide of the present invention must have a BET specific surface area of 0.6 m ² · g ⁻¹ or less. The larger the BET specific surface area, the better the contact with the electrolytic solution and the conductive material, which is advantageous for high-rate charge / discharge performance, but the deterioration of high-temperature stability and the workability at the time of electrode preparation become worse. Therefore, the BET specific surface area is preferably 0.6 m ² · g ⁻¹ or less.

  In the lithium manganese oxide of the present invention, it is essential that the average crystallite diameter determined by the Hall method is 1000 angstroms or more and 1400 angstroms or less. When the average crystallite diameter is in the above range, good high-rate charge / discharge characteristics can be achieved even in the range of the average particle diameter and the BET specific surface area of the present invention.

  In the lithium manganese oxide having a spinel structure, the charge / discharge reaction proceeds by the lithium in the 8a site diffusing in the solid phase through the empty 16c site. Lithium ion mobility, that is, high-rate charge / discharge performance may be affected by the degree of development of the lithium diffusion path inside the solid phase. Therefore, the higher the crystal structure, the better the high-rate charge / discharge performance. It is thought that it becomes. In hybrid type electric vehicle battery applications, charging / discharging at least 5 C (conditions for charging or discharging the battery capacity in 1/5 hour) or more is necessary. Details are unknown, but according to the inventors' investigation. When the average crystallite size obtained by the Hall method is 1000 angstroms or more and 1400 angstroms or less, a significant improvement in the high rate characteristics is recognized. The average crystallite diameter is an index representing the degree of repetitive development of the unit cell. The larger this value, the more the crystal is developed. According to the Hall method of the present invention, the diffraction of each diffraction peak obtained by powder X-ray diffraction measurement is described, for example, on page 75 of the X-ray diffraction manual revised fourth edition (Rigaku Corporation). In this method, the average crystallite diameter is obtained from the position and the spread of the peak, that is, the half width.

The LiCoO ₂ and LiNiO _{2 with} a layered structure cause two-dimensional diffusion in the lithium solid phase, whereas the spinel structure causes lithium diffusion in the solid phase through a three-dimensionally developed lithium diffusion path. However, as in the present invention, the average particle diameter is 5 to 20 μm, the BET specific surface area is 0.6 m ² · g ⁻¹ or less, and the average crystallite diameter is 1000 angstroms or more and 1400 angstroms or less. This makes it possible for the first time to achieve both the ease of electrode fabrication and the high-rate charge / discharge characteristics.

  The lithium manganese oxide of the present invention has at least one selected from manganese compounds having an average oxidation number of manganese of 8/3 or more, lithium compounds, and Ni, Co, Fe, Cr, Cu, B, Al, Ga, and In. After the mixture with the metal material of more than one kind is first baked at a temperature of 500 ° C. or lower, a second baking is performed at a temperature exceeding 500 ° C. and 950 ° C. or lower, followed by cooling to 500 ° C. It is synthesized by performing at a rate of 20 ° C. or less per hour. First, by performing the first firing at a temperature of 500 ° C. or lower, the complexing reaction with the manganese compound, the lithium compound, and the metal element M easily proceeds uniformly. By firing this, a lithium manganese composite oxide having a sufficiently developed crystal structure can be synthesized. Furthermore, since lithium manganese oxide exhibits the property of releasing and absorbing oxygen at high temperatures, cooling after the second firing should be performed at a rate of 20 ° C. or less per hour in consideration of oxygen reabsorption during the temperature lowering process. However, it is important in synthesizing a lithium manganese composite oxide having a crystal structure with a uniform composition. Note that the firing is preferably performed in the air or in a gas stream having an oxygen content of 18% or more. In particular, this condition is more preferable in the second firing.

  In the synthesis of the lithium manganese oxide of the present invention, it is important to use a manganese compound having an average oxidation number of manganese of 8/3 or more. Any manganese compound may be used as long as the average oxidation number of manganese in the compound is 8/3 or more. Although not limited to the present invention, for example, oxides include oxides such as so-called manganese dioxide, manganese trioxide, hydrated manganese oxide (MnOOH), and manganese trioxide in various crystal forms, and manganese compounds. Examples include manganese oxides having an average oxidation number of 8/3 or more of manganese synthesized by heat treatment at a temperature of 500 ° C. or higher. Although details are unknown, among these, the use of manganese sesquioxide makes it easy to synthesize a lithium manganese composite oxide having a crystal structure with a uniform composition.

  As the lithium compound used for the synthesis, any compound may be used as long as it undergoes a complexing reaction at a temperature of 500 ° C. or less with a compound having an average oxidation number of manganese of 8/3 or more. Although the present invention is not limited, for example, lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, lithium iodide and the like are exemplified, but in order to perform mixing more uniformly, the average particle size is 10 μm. The following lithium compounds are preferably used.

  As the metal element M used for the synthesis, any compound may be used as long as it is a compound that starts a complexing reaction with a manganese raw material and a lithium raw material at a temperature of 500 ° C. or lower. Although this invention is not restrict | limited, For example, carbonate, nitrate, hydroxide, an oxide, etc. of Ni, Co, Fe, Cr, Cu, B, Al, Ga, and In are illustrated.

  As the negative electrode of the lithium secondary battery of the present invention, a lithium metal, a lithium alloy, or a compound that occludes lithium in advance and can occlude and release lithium can be used.

  Examples of the lithium alloy include, but are not limited to, the lithium / tin alloy, lithium / aluminum alloy, and lithium / lead alloy.

  The compound capable of occluding and releasing lithium is not limited to the present invention, and examples thereof include carbon materials such as graphite and graphite, iron oxides, and cobalt oxides.

  Further, the electrolyte of the lithium secondary battery of the present invention is not particularly limited. For example, carbonates such as prolene carbonate and diethyl carbonate, sulfolanes such as sulfolane and dimethyl sulfoxide, lactones such as γ-butyrolactone, dimethyl sulfoxide and the like A solution in which at least one of lithium salts such as lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, and trifluoromethanesulfonic acid is dissolved in at least one organic solvent of Inorganic and organic lithium ion conductive solid electrolytes can be used.

A mixture of a manganese compound having an average oxidation number of manganese of 8/3 or more, a lithium compound, and at least one metal material selected from Ni, Co, Fe, Cr, Cu, B, Al, Ga, and In by firing, the general formula _{Li 1 + X Mn 2-Y} -Z M Z O 4 + δ ( wherein M be a Ni, Co, Fe, Cr, Cu, B, Al, Ga, at least one or more selected from in 0 ≦ X ≦ 1/3, 0 ≦ Y ≦ 1/3, 0 <Z ≦ 0.25, −0.14 ≦ δ ≦ 0.5), the average particle diameter is 5 to 20 μm, and the BET ratio It is possible to synthesize a lithium-manganese composite oxide having a novel spinel crystal structure having a surface area of 0.6 m ² · g ⁻¹ or less and an average crystallite size determined by the Hall method of 1000 angstroms or more. Positive electrode of lithium secondary battery It has been found that by using it as an active material, a manganese-based lithium secondary battery having high-rate charge / discharge characteristics and high-temperature stability that cannot be achieved by conventional materials can be constructed.

  Finding a lithium-manganese composite oxide having excellent high-rate charge / discharge characteristics is an industrially useful finding.

It is a figure which shows the embodiment of the battery comprised by the Example and the comparative example.

  Examples are shown below as specific examples of the present invention, but the present invention is not limited to these examples.

  The powder X-ray diffraction measurement and the average crystallite diameter ε in Examples and Comparative Examples of the present invention were calculated by the following methods.

Powder X-ray diffraction measurement Measurement model MXP3 manufactured by Mac Science
Irradiation Cu Kα rays
Measurement mode Step scan
Scan condition 0.04 ° as 2θ
Measurement time 5 seconds
Measurement range 2θ as 5θ to 80 °
Calculation of average crystallite diameter Hall method: β · cos θ / λ = 2 · η · sin θ / λ + 1 / ε Measure the profile of two or more diffraction lines, and β · cos θ / λ is 2 · η on the Y axis. The reciprocal of the intercept of the straight line obtained by plotting sin θ / λ on the X axis is the average crystallite diameter value ε.

  Here, β: half width, λ: measured X-ray wavelength, θ: black angle of diffraction line ε: average size of crystallite diameter, η: value of non-uniform strain of crystal.

  The BET specific surface area was measured by a nitrogen adsorption method, and the average particle diameter was measured by a microtrack.

[Production of lithium manganese composite oxide]
Example 1 (Synthesis of LiMn _1.8 Al _0.2 O ₄ )
As Example 1, LiMn _1.8 Al _0.2 O ₄ was prepared by the following method.

  Lithium carbonate, aluminum hydroxide, and manganese sesquioxide are mixed at a molar ratio of Li: Mn: Al ratio of 1.0: 1.8: 0.2, and then the first firing is performed in the atmosphere as 450. Firing was performed at a temperature of 12 ° C. for 12 hours. Next, this was cooled to room temperature, pulverized and mixed, and then baked in the atmosphere at 800 ° C. for 24 hours as the second baking. From the result of the powder X-ray diffraction measurement, it was found that the obtained compound had a spinel structure. As a result of chemical composition analysis of the product, Table 1 shows the value of ε, the average particle diameter, and the BET specific surface area.

Example 2
(Synthesis of LiMn _1.8 Ni _0.2 O ₄ )
Example 2 is the same as Example 1 except that nickel hydroxide is used as the metal element and mixed so that the molar ratio of Li: Mn: Ni is 1.0: 1.8: 0.2. Thus, a lithium manganese composite oxide was synthesized. From the result of the powder X-ray diffraction measurement, it was found that the obtained compound had a spinel structure. As a result of chemical composition analysis of the obtained compound, Table 1 shows the value of ε, the average particle diameter, and the BET specific surface area.

Example 3
(Synthesis of LiMn _1.9 Co _0.1 O ₄ )
Example 3 is the same as Example 1 except that cobalt hydroxide is used as the metal element and mixed so that the molar ratio of Li: Mn: Co is 1.0: 1.9: 0.1. Thus, a lithium manganese composite oxide was synthesized. From the result of the powder X-ray diffraction measurement, it was found that the obtained compound had a spinel structure. As a result of chemical composition analysis, Table 1 shows the values of ε, average particle diameter, and BET specific surface area.

Example 4
(Synthesis of LiMn _1.8 Cr _0.2 O ₄ )
Example 4 was the same as Example 1 except that chromium trioxide was used as the metal element and mixed such that the molar ratio of Li: Mn: Cr was 1.0: 1.8: 0.2. Thus, a lithium manganese composite oxide was synthesized. From the result of the powder X-ray diffraction measurement, it was found that the obtained compound had a spinel crystal structure. As a result of chemical composition analysis of the obtained compound, Table 1 shows the values of ε, average particle diameter, and BET specific surface area.

Example 5
(Synthesis of LiMn _1.8 Cu _0.2 O ₄ )
Example 5 was carried out except that copper nitrate trihydrate was used as the metal material and the mixture was mixed so that the molar ratio of Li: Mn: Cu was 1.0: 1.8: 0.2. In the same manner as in Example 1, a lithium manganese composite oxide was synthesized. From the result of the powder X-ray diffraction measurement, it was found from the result of the powder X-ray diffraction measurement that the obtained compound had a spinel crystal structure. As a result of chemical composition analysis of the obtained compound, Table 1 shows the values of ε, average particle diameter, and BET specific surface area.

Comparative Example 1
As Comparative Example 1, LiMn _1.8 Al _0.2 O ₄ was synthesized in the same manner as in Example 1 except that the cooling rate after the second firing was 100 ° C. per hour. From the result of the powder X-ray diffraction measurement, it was found that the obtained compound was a spinel single phase. As a result of chemical composition analysis, Table 1 shows the values of ε, average particle diameter, and BET specific surface area.

[Battery configuration]
The lithium manganese composite oxide produced in Examples 1 to 5 and Comparative Example 1 was mixed with a conductive agent polytetrafluoroethylene and acetylene black (trade name: TAB-2) in a weight ratio of 2: 1. Mixed. 75 mg of the mixture was formed into a pellet shape on a 16 mmφ mesh (SUS 316) at a pressure of 1 ton · cm ⁻² , and then dried under reduced pressure at 200 ° C. for 5 hours.

This was used for the positive electrode 3 in FIG. 1, and for the negative electrode 5 in FIG. 1, a lithium piece cut out from a lithium foil (thickness 0.2 mm) was used, and the electrolyte solution was propylene carbonate and dimethyl carbonate. ratio of volume 1: 2 mixed solvent of the organic electrolyte prepared by dissolving lithium hexafluorophosphate in a concentration of 1 mol · dm ^-3 impregnated into 4 of the separator of Figure 1, Figure 1 of the cross-sectional area 2 cm ² The battery shown in 1 was constructed.

[Evaluation of rate characteristics]
Using the battery prepared by the above method, charge and discharge were repeated for 5 cycles at a constant current of 0.4 mA · cm ⁻² and a battery voltage between 4.5V and 3.5V. Next, the battery was charged with a constant current of 0.4 mA · cm ⁻² until the battery voltage reached 4.5 V, and then discharged with a constant current of 5 mA · cm ⁻² to 3.5 V. Table 1, the ratio of the discharge capacity at 5 mA · ^{cm -2} to the discharge capacity at 0.4 mA · ^{cm -2} at the fifth cycle, i.e. exhibited a capacity retention rate.

  The lithium manganese oxides synthesized in Examples 1 to 5 all showed a high capacity retention rate of about 95%. On the other hand, the capacity retention rate of the lithium manganese composite oxide synthesized in the comparative example was 90%.

1: Positive electrode lead wire 2: Positive electrode current collecting mesh 3: Positive electrode 4: Separator 5: Negative electrode 6: Negative electrode current collecting mesh 7: Negative electrode lead wire 8: Container

Claims (2)

Formula _{Li 1 + X Mn 2-Y} -Z M Z O 4 + δ ( wherein M is at least one element selected Ni, Co, Fe, Cr, Cu, B, Al, Ga, from an In, 0 ≦ X ≦ 1/3, 0 ≦ Y ≦ 1/3, 0 <Z ≦ 0.25, −0.14 ≦ δ ≦ 0.5), the average particle diameter is 5 to 20 μm, and the BET specific surface area is 0. 1.6 m ² · g ⁻¹ or less, and the average crystallite size determined by the Hall method is 1000 angstroms or more and 1400 angstroms or less, for a positive electrode active material of a lithium battery having a spinel crystal structure Lithium manganese composite oxide. The lithium manganese composite oxide for a positive electrode active material of a lithium battery according to claim 1, wherein at least one substance selected from lithium, a lithium alloy and a compound capable of occluding and releasing lithium is used as a negative electrode, a nonaqueous electrolyte is used as an electrolyte, Lithium secondary battery used for

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