JP2003346807A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery using lithium manganese compound oxide with high energy density for suppressing degradation of the discharging capacity, in particular, for suppressing degradation of the discharging capacity at high temperatures. <P>SOLUTION: A general formula of a lithium-manganese compound oxide having a spinel structure is expressed by Li<SB>1+x</SB>Mn<SB>2-x-y</SB>Me<SB>y</SB>O<SB>4</SB>(where, Me is a metal element other than manganese, x satisfies inequalities 0<x≤0.2, and y satisfies inequalities 0<y≤0.15). The lithium-manganese compound oxide of the lattice constant a to satisfy an inequality a≤8.215 Å, the specific surface area of ≤1.5 m<SP>2</SP>/g, and the grain size of 5-30 μm is used for the positive electrode active material. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte.

[0002]

2. Description of the Related Art In recent years, portable electronic devices have become more portable.
As cordless technology has rapidly progressed, lithium ion secondary batteries have been put into practical use as power supplies for small electronic devices. For lithium ion secondary batteries, since it was reported that lithium cobalt oxide was useful as a positive electrode active material,
Research and development on lithium-transition metal composite oxides have been actively advanced, and lithium cobaltate, lithium nickelate, lithium manganate, and the like have been known as main positive electrode active materials so far. Of these, lithium manganate has recently received particular attention because it is superior to lithium cobalt oxide and lithium nickelate in safety at the time of battery abnormality and cost performance due to resource reserves.

[0003]

In a battery using a lithium manganese composite oxide as a positive electrode active material, problems such as reduction in discharge capacity and output due to repeated charging and discharging are observed. Notable when used in The main causes include volume change of lithium manganese composite oxide due to repeated charge and discharge, phase transition due to Jahn-Teller distortion, and dissolution of manganese ions from lithium manganese composite oxide into electrolyte at high temperatures. It is important to overcome the problem and to suppress a decrease in discharge capacity and improve high-temperature characteristics.

Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery using a lithium manganese composite oxide having a high energy density and a reduced discharge capacity, and in particular, a reduced discharge capacity at a high temperature. It is to provide a battery.

[0005]

The non-aqueous electrolyte secondary battery of the present invention has a general formula Li _{1 + x} Mn _2-xy Me _y O ₄ (where Me represents a metal element other than manganese, and x is 0) <X ≦ 0.2, y is 0 <y ≦ 0.15
Is a lithium manganese composite oxide having a spinel structure, wherein the lattice constant a is a ≦ 8.215.
Å A non-aqueous electrolyte secondary battery characterized by using a lithium manganese composite oxide having a specific surface area of 1.5 m ² / g or less and an average particle size of 5 to 30 μm as a positive electrode active material.

The lattice constant a obtained from X-ray diffraction measurement is a
≤8.215Å, specific surface area 1.5m ² / g or less, average particle size 5-30
By using a lithium manganese composite oxide having a thickness of μm as a positive electrode active material, it is possible to suppress a decrease in discharge capacity due to repetition of charge and discharge, and particularly to suppress a decrease in discharge capacity at a high temperature.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the results of X-ray diffraction measurement (Cu
(Kα ray) based on the lattice constant a obtained by Rietveld analysis based on the Rietveld use a lithium manganese composite oxide having a spinel structure represented by a ≤ 8.215 Å, more preferably a ≤ 8.21 Å Is good. In the lithium manganese composite oxide having the lattice constant in this range, the life characteristics, particularly the high temperature characteristics, are improved, and the effect is particularly remarkable in the range of a ≦ 8.21%. It is considered that this is because the crystal structure is stabilized, the volume change during the charge / discharge process is reduced, and the decrease in adhesion within the electrode plate is suppressed.

[0008] Further, the life performance is not improved only by the lattice constant, and the lithium manganese composite oxide to be used is shown in FIG.
As shown in the above, the specific surface area of the particles is preferably 1.5 m ² / g or less, more preferably 1.0 m ² / g or less, and further preferably 0.8 m ² / g or less. By setting the specific surface area in this range, it is possible to suppress the elution of Mn, but if the specific surface area is more than that, it is necessary to increase the amount of the conductive additive and the binder in the positive electrode mixture. is there. The average particle size of the active material is desirably 5 to 30 μm from the viewpoint of improving the electrode density and the electrode strength. As shown in FIG. 4, the lithium manganese composite oxide particles preferably have a shape in which 0.5 to 10 μm polyhedral primary particles are aggregated to form spherical secondary particles having an average particle size of 5 to 30 μm. However, the shape itself is not limited to this.

In the lithium-manganese composite oxide according to the present invention, the value of the standard deviation σ when the particle size distribution is measured is expressed as 0.15 ≦ σ ≦ 0.30. In the lithium manganese composite oxide having the standard deviation in the range, the distribution state of the particle diameter is moderate, and the particle diameter is dispersed to some extent, so that when the paste is applied to the base material, large particles are distributed. However, an effect that small particles enter the gap and fill the gap can be expected, and the obtained electrode plate can be manufactured with a small gap and a large tap density. In a battery using this electrode plate, problems such as bending and peeling which may occur in the process of winding the electrode plate can be eliminated, and a battery having a high energy density per volume when the porosity is almost the same can be obtained. preferable. When a positive electrode mixture is applied to a base material to produce an electrode plate, and when the electrode plate is wound, problems such as bending are suppressed, and a battery having a large energy density can be produced at the time of producing a battery.

In the lithium manganese composite oxide according to the present invention, the lattice constant a determined by Rietveld analysis
Indicates that a> 8.184Å. In the lithium manganese composite oxide, the initial discharge capacity tends to decrease as the lattice constant decreases, and the initial discharge capacity also decreases in the lithium manganese composite oxide where the lattice constant a shows a ≦ 8.184Å, and the value is 80%.
A battery with poor energy density, such as below mA / g. Further, even when the lattice constant was a smaller value, no further effect of improving the life characteristics was confirmed.

The above-mentioned lithium manganese composite oxide has a general formula Li _{1 + x} Mn _2-xy Me _y O ₄ (where Me represents a metal element other than manganese, x is 0 <x ≦ 0.2, and y is 0 <Y ≦ 0.15) and has a spinel structure. In the general formula, Me is a metal element other than manganese, for example,
Mg, Al, Cr, Ni, Fe, Co and Cu, and the like.
One type or a combination of two or more types is used. This Me is originally in the crystal structure of the lithium manganese composite oxide of the present invention.
Some sites that should be occupied by Mn are replaced with Mn. Me is preferably a trivalent stable metal from the viewpoint of discharge capacity, and more preferably Al.

In the present invention, it is possible to use a lithium manganese composite oxide as a main component and mix it with another lithium transition metal composite oxide. Other lithium transition metal composite oxides include, for example, lithium cobalt composite oxide, lithium nickel composite oxide, and the like. When a mixture is used as the positive electrode active material, the weight ratio of the lithium manganese composite oxide is preferably from 60 to 90% of the weight of the positive electrode active material.

As the negative electrode material in the present invention, for example, lithium metal, lithium alloy or carbon material is used. As the carbon material, artificial graphite having high crystallinity, natural graphite, easily graphitized carbon having low crystallinity, hardly graphitized carbon, or the like may be used, and these may be mixed and used.

The non-aqueous electrolyte used in the present invention has a high dielectric constant.
Ethylene carbonate (EC), propylene carbonate
Nate (PC), γ-butyrolactone (γ-BL), dimethyl sulfone
Dimethyl carbonate is used for low-viscosity solvents such as foxide (DMSO).
(DMC), diethyl carbonate (DEC), ethyl methyl carbonate
Non-professionals such as carbonate (EMC) and dimethoxyethane (DME)
A mixture of at least one or more organic solvents
Lithium hexafluorophosphate as a lithium salt soluble in the solvent
Um (LiPF₆), Lithium tetrafukaborate (LiBF _Four), Perchlorine
Lithium oxide (LiClO_Four), Lithium hexafuca arsenate (LiAsF₆)
Which is used. Add such electrolyte into the battery
Although the amount is not particularly limited, the amount of the positive electrode active material or the negative electrode material
And the required amount can be used depending on the size of the battery.

[0015] Instead of the above liquid electrolyte, a solid ionic conductive polymer electrolyte can also be used. When the polymer electrolyte membrane is made of polyethylene oxide, polyacrylonitrile, polyethylene glycol, or a modified product thereof, it is lightweight and flexible, and is advantageous when used for a wound electrode plate. Furthermore, the ion conductive polymer electrolyte membrane and the organic electrolyte can be used in combination. In addition, as the electrolyte, in addition to the polymer electrolyte,
A mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, an inorganic solid powder bound by an organic binder, or the like can be used.

The non-aqueous electrolyte secondary battery according to the present invention generally comprises a positive electrode, a negative electrode and a combination of a separator and a non-aqueous electrolyte. The separator is a porous polyvinyl chloride film. Such a porous polymer membrane or a lithium ion or ionic conductive polymer electrolyte membrane can be used alone or in combination.

[0017]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited thereto without departing from the gist of the present invention. In the synthesis of the lithium-manganese composite oxide of the present invention, lithium hydroxide and lithium carbonate as lithium raw materials, manganese dioxide and manganese carbonate as manganese raw materials, and hydroxides and oxides of each metal for metal species other than manganese Are used.

[0018] Lithium hydroxide, manganese dioxide and aluminum hydroxide were mixed at a predetermined ratio and fired in an electric furnace to obtain several kinds of lithium manganese composite oxides having different lattice constants. 800 ℃ ~ 900 ℃, firing time is
The firing was performed for 5 to 15 hours. In the X-ray diffraction measurement of the product (RINT2400, manufactured by Rigaku Corporation), only peaks attributed to spinel-type manganese were observed, and peaks attributed to impurities and the like were not observed. Using the results of the X-ray diffraction measurement, Rietveld analysis (Rietbelt analysis program RI
ETAN) to calculate the lattice constant. The average particle size and particle size distribution of the product were measured using a particle size distribution analyzer (Shimadzu laser diffraction type particle size analyzer SALD-2000J) with the relative complex number set to 2.00 + 0.05i, and the particle size distribution was measured.
In the measurement, a 0.1% aqueous solution of sodium hexametaphosphate was used as a dispersion medium for the sample, and the measurement was performed after irradiating ultrasonic waves for 5 minutes. The specific surface area of the product was measured by a BET method using a specific surface area measuring device (Gemini 2370 manufactured by Shimadzu).

With respect to the production of the above-mentioned positive electrode plate of the lithium manganese composite oxide, graphite was used as a conductive agent, and polyvinylidene fluoride was used as a binder. A lithium manganese composite oxide, graphite and polyvinylidene fluoride were mixed at a predetermined ratio, and N-methylpyrrolidone was used for viscosity adjustment. The obtained positive electrode mixture was applied to an aluminum substrate at a predetermined application weight by a doctor blade method, and dried at a predetermined temperature under vacuum to prepare a positive electrode plate. The positive electrode active materials used were 22 in total, and the compositions and the results of the above measurements are summarized in Table 1 below. The composition formula is represented by the elements of Me and their ratios and the ratio of Li and Me in the general formula Li _{1+ x} Mn _2-xy Me _y O ₄ .

Using the above-described electrode plate, the electrode plate was bent at 180 °, and the presence or absence of cracks and peeling of the mixture layer showing bending was examined. The results are shown in the right column of Table 1. Further, a triode-type glass cell was assembled using a sample showing the above favorable results, using a positive electrode plate as a working electrode, and lithium metal as a counter electrode and a reference electrode. Lithium hexafluorophosphate (LiPF ₆ ) as a supporting salt for the electrolyte and ethylene carbonate for the solvent
A mixed solution of (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) was used. A charge / discharge cycle was performed using the prepared cell at a charge current density of 1.0 mA / cm ² , a discharge current density of 2.0 mA / cm ² , and a voltage range of 3.0 to 4.3 V. 50 cycles were performed at a temperature of 60 ° C., and the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle was defined as the capacity retention. Table 1 shows the relationship between the obtained initial discharge capacity, the capacity retention at 60 ° C., and the lattice constant, and a graph was created based on Table 1. The results are shown in FIGS.

[Table 1]

For a sample having a lattice constant of 8.215 ° or less, 6
0 ° C-50 cycles capacity retention of 90% or more, lattice constant 8.2
1% or less samples have a capacity retention of 95% or more,
Shows good high temperature properties. For samples with a lattice constant of 8.19Å or more, the initial discharge capacity is 90mAh / g or more,
Shows good discharge capacity.

The lattice constant a is a ≦ 8.215 ° and the specific surface area is 1.5 m ²
/ g or less, for a sample having an average particle size of 5 to 30 μm,
The capacity retention of 0 cycles is 90% or more, indicating good high-temperature characteristics.

[0023]

According to the present invention, Li _{1 + x} Mn _2-xy Me _y O ₄ (where Me represents a metal element other than manganese, x is 0 <x ≦ 0.2, y is 0 <y ≦ 0.15
Is a lithium manganese composite oxide having a spinel structure, wherein the lattice constant a is a ≦ 8.215.
Å By using a lithium manganese composite oxide having a specific surface area of 1.5 m ² / g or less and an average particle size of 5 to 30 μm as a positive electrode active material, the energy density is high, the discharge capacity is reduced, especially at high temperatures. A battery with a reduced discharge capacity can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a lattice constant and a capacity retention.

FIG. 2 is a diagram showing a relationship between a lattice constant and an initial discharge capacity.

FIG. 3 is a diagram showing a relationship between specific surface area and capacity retention.

FIG. 4 is a view showing a particle shape of a positive electrode active material according to one embodiment of the present invention.

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Claims (1)

[Claims] 1. The general formula Li _{1 + x} Mn _2-xy Me _y O ₄ (where Me represents a metal element other than manganese, x is 0 <x ≦ 0.2, and y is 0 <y ≦
A lithium manganese composite oxide having a spinel structure, wherein the lattice constant a is a ≦ 8.21.
5. A non-aqueous electrolyte secondary battery using a lithium manganese composite oxide having a specific surface area of 1.5 m ² / g or less and an average particle size of 5 to 30 μm as a positive electrode active material.