JP2647015B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art A nonaqueous electrolyte secondary battery using lithium as a negative electrode active material has a high voltage and a high energy density, and thus is used not only as a power source for portable electronic devices but also as a distributed power storage battery. It is also attracting attention and is being actively developed. Although some batteries have been put to practical use, their battery capacity, cycle life, and reliability are still insufficient.

Conventionally, as a non-aqueous electrolyte secondary battery, many batteries using a positive electrode active material such as a transition metal oxide, a transition metal chalcogenide, or a composite oxide of lithium and a transition metal have been proposed. Among these positive electrode active materials, batteries using vanadium pentoxide (V ₂ O ₅ ) as the positive electrode active material are expected to be high energy density batteries because of their high operating potential. Therefore, in order to improve battery characteristics, application of amorphous V ₂ O ₅ (JP-A-4-24828) and ultrafine powder V ₂ O ₅ (JP-A-62-195853) to the positive electrode active material is also considered. Has been proposed. However, none of the proposals has sufficient battery capacity.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to provide V ₂
An object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent characteristics by improving the battery shape by improving the powder shape of O ₅ .

[0005]

SUMMARY OF THE INVENTION The present invention provides a non-aqueous electrolyte having a non-aqueous electrolyte in which lithium ions are conducted between a negative electrode having lithium as a negative electrode active material and a positive electrode having vanadium pentoxide as a positive electrode active material. In the water electrolyte secondary battery, the value of the X-ray diffraction using vanadium pentoxide using CuKα ray is such that the half value width of the diffraction peak on the {200} plane at a diffraction angle (2θ) of 15.1 to 15.5 ° is 0. .13 ° or more.

[0006] The reference half width is determined by the desired performance (eg, energy density) and the properties of the sample (eg, manufacturing method, etc.).
Can be changed in accordance with

Further, the present invention provides a non-aqueous electrolyte secondary battery having a non-aqueous electrolyte in which lithium ions are conducted between a negative electrode having lithium as a negative electrode active material and a positive electrode having vanadium pentoxide as a positive electrode active material. In the method for evaluating a positive electrode for a battery, the vanadium pentoxide was measured by X-ray diffraction using CuKα radiation, and a diffraction angle (2θ) of 15.1 to 1 was measured.
The half-width value of the diffraction peak on the {200} plane at 5.5 ° is compared with a preset value, and the magnitude of the half-width value with respect to the set value is determined.

The set value (value used as a criterion for determination) can be arbitrarily set depending on the desired performance (eg, energy density). Further, it can be set according to the properties of the target sample (for example, the manufacturing method or the like).

In order to improve the battery capacity, it is necessary to easily insert lithium ions into the positive electrode active material and desorb lithium ions from the positive electrode active material. For this purpose, it is important to widen the reaction field where lithium ions are inserted and desorbed. Good symmetry crystal structure (e.g., cubic) In the case of the active material, the insertion of lithium ions from any crystal plane is susceptible of leaving, V ₂
In the case of an active material having low symmetry, such as O ₅ (orthorhombic system), insertion of lithium ions,
With respect to desorption, the crystal planes are not equivalent. In other words, a crystal plane in which insertion and desorption of lithium ions are easily performed, or a crystal plane in which insertion and desorption of lithium ions are unlikely to occur occurs. Therefore, evaluation and selection of a powder having a large absolute amount of the crystal plane on the powder surface where lithium ions can be easily inserted and desorbed, and using the powder for the positive electrode are the key points for improving the performance of the battery.

As a result of various studies from the above viewpoints, the specific surface area or particle size of the powder is not sufficient for evaluating the activity of the positive electrode active material powder, and the crystal plane on which lithium ions are inserted and desorbed is not sufficient. It was found that it was important to evaluate the absolute amount of the positive electrode active material occupying the powder surface. To this end, it has been found effective to examine the powder shape based on the half width of the diffraction peak in X-ray diffraction. According to the X-ray diffraction method, as the half width of the diffraction peak on the {hk1} plane increases, the particle size of the crystal grains in the direction perpendicular to the {hk1} plane decreases. This means that ｛hk
The powder having a larger half-width of the diffraction peak on the 1｝ plane has a higher Δh
This indicates that the surface area of the k1｝ plane is larger. The activity of the positive electrode active material powder for lithium ion insertion and desorption can be evaluated using the half width of the diffraction peak of the crystal plane involved in the insertion and desorption of lithium ions. By using a highly active cathode active material obtained by such evaluation, a highly reliable nonaqueous electrolyte secondary battery can be provided.

The V ₂ O ₅ cathode active material used in the present invention can be obtained by various production methods. For example, sputtering, atomization and thermal decomposition of an aqueous solution of ammonium metavanadate, or thermal decomposition of ammonium metavanadate are possible. To form a positive electrode using this positive electrode active material, a conductivity-imparting powder such as acetylene black is added and kneaded, and this is applied to a support such as stainless steel. Also, if sputtering is performed on a support such as a stainless steel or platinum substrate, it can be used as it is as a positive electrode. The object of the present invention can be achieved by using any of graphite-based carbon materials, amorphous-based carbon materials, lithium and lithium alloys for the negative electrode.

Further, as the electrolyte, propylene carbonate, 2-methyltetrahydrofuran, dioxolen, tetrahydrofuran, 1,2-dimethoxyethane,
One or more aprotic polar organic solvents selected from ethylene carbonate, γ-butyrolactone, dimethylsulfoxide, acetonitrile, formamide, dimethylformamide, nitromethane, etc. may be LiClO ₄ , LiAl
Generally used in batteries using lithium as a negative electrode active material, such as an organic electrolyte in which lithium salts such as Cl ₄ , LiBF ₄ , LiPF ₆ , and LiAsF ₆ are dissolved, a solid electrolyte using lithium ions as a conductor, or a molten salt. Known electrolytes can be used. Further, the effect of the present invention is not impaired at all even if a microporous separator is used as required in the structure of the battery.

[0013]

V ₂ O ₅ is a metal oxide having a layered structure, and its crystal form is orthorhombic. Therefore, the properties of a highly anisotropic crystal structure called a layered structure are reflected in the lithium ion insertion or desorption reaction accompanying the charge and discharge of the battery. Between the layers composed of vanadium and oxygen (parallel to the ab plane),
Lithium ions are inserted with discharge. But,
Due to the anisotropy of the crystal structure, lithium ions in V ₂ O ₅ easily move in a direction parallel to the ab plane, but are extremely hard to move in a direction perpendicular to this plane (parallel to the c-axis). For this reason, in order to easily insert and remove lithium ions, a plane parallel to the c-axis, that is, {h00} or {0k0}
It is important to increase the absolute value of the plane having the plane index of the entire surface of the crystal grain. To evaluate the absolute value occupied by the surface where lithium ions are easily inserted and desorbed,
It is effective to evaluate with the half value width of the peak of the diffraction line of the plane having the plane index of {h00} or {0k0}. V ₂ O ₅
In, the diffraction line satisfying such conditions is a {200} plane diffraction line having a diffraction angle of 15.1 to 15.5 ° (in the case of CuKα ray). By evaluating the positive electrode active material by the half width of the diffraction peak on the {200} plane, it is possible to evaluate the magnitude of the absolute amount of the crystal plane in which lithium ions can be easily inserted or desorbed. Powder can be selected. That is, when the half-width of the peak of the diffraction line on the {200} plane becomes a certain value or more, insertion of lithium ions,
The absolute amount of the surface involved in desorption occupying the powder surface is increased, so that not only the insertion and desorption of lithium ions during charging and discharging easily occur, but also a high battery capacity is obtained. Therefore, by using such a positive electrode active material powder, a high-performance nonaqueous electrolyte secondary battery can be obtained.

[0014]

The present invention will be described below by way of examples. still,
The present invention is not limited to the following examples. In the following examples, the preparation and evaluation of the battery were all performed in an argon atmosphere.

[0015] sputtered V ₂ O ₅ under Ar in Example 1 a platinum substrate (1 × 2 cm), then was crystallized by heat treatment in an air atmosphere. Heat treatment temperature is 400,450,500,55
0,600,650 ° C., and the processing time was 20 hours for each temperature. The amount of sputtered V ₂ O ₅ was determined by emission spectroscopy. Table 1 shows the obtained half widths of the X-ray diffraction peaks of the {200} plane of V ₂ O ₅ . To evaluate the charge / discharge characteristics of V ₂ O ₅ , a Li-Pb-La alloy powder was prepared by using a mixed solvent solution of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) having a concentration of 1.0 M of LiPF ₆ as an electrolyte. Was used as a counter electrode. The composition of the Li-Pb-La alloy is 3.5: 1.0: 0.03 in atomic ratio. As the separator, a polypropylene nonwoven fabric and a microporous film were used. The charge / discharge test was performed at a constant current and the current density was 0.0
5 mA / cm ² . The final voltage was 3.5 V during charging and 1.5 V during discharging. Table 1 shows the obtained energy density per unit weight of the V ₂ O ₅ positive electrode active material.

[0016]

[Table 1]

When the heat treatment temperature was in the range of 400 to 600 ° C., the half width was as large as 0.15 to 0.38 °, and the energy density was as high as 650 to 700 Wh / kg. On the other hand, in the case of 650 ° C., since the half width is as small as 0.10 ° and the activity is low, the energy density is 400 Wh /
The value was as small as kg. When incorporated as a battery, 600 Wh / kg is required to be used as a high energy type battery.
It is desirable to use an electrode having a certain energy density. In order to further obtain a high-performance battery, it is preferable to have an energy density of about 650 Wh / kg. As a criterion for the half width, the electrode can be evaluated using a desired criterion such as 0.13 or 0.18. Further, when the half value width is determined to be 0.3 or more, a higher performance battery can be produced.

EXAMPLE 2 A mist of an aqueous solution of ammonium metavanadate (concentration: 0.02 to 0.4 mol / l) generated by an ultrasonic atomizer was introduced into a pyrolysis furnace controlled at 300 ° C. by a carrier gas, and pyrolyzed. Pyrolysis powder was obtained by collecting with a dust collector. The obtained pyrolyzed powder was heat-treated at 600 ° C. for 5 hours to be crystallized. Ethylene-propylene-diene copolymer (EPD) as a binder to V ₂ O ₅ powder obtained by heat treatment
A 4.0 wt% xylene solution of M) and 9.0 wt% of acetylene black as a conductive agent were added and kneaded to form a paste. This is an expanded metal made of SUS430 (1 × 2c
m) and vacuum dried at room temperature to obtain a positive electrode. Note that the negative electrode and the separator are as described in Example 1. A battery was manufactured using the above-described positive electrode, separator, and negative electrode. The charge / discharge test was performed at a constant current, and the current density was 1.0 mA / cm ² . The end voltage was 3.5 V during charging and 1.5 V during discharging, as in Example 1. Table 2 shows the characteristics of the positive electrode active material.

[0019]

[Table 2]

The positive electrode active material having a half width of 0.16 to 0.30 ° has a high energy density of 650 Wh / kg or more, while the positive electrode active material having a small half value width of 0.09 ° has an energy density of 390 Wh / kg. The value was as low as kg. For example, as a criterion for the half width, 0.13 used in Example 1 or 0.16 for evaluating a higher performance battery can be used.

Example 3 In the same manner as in Example 2, V ₂ O ₅ powder was obtained from ammonium metavanadate. In this example, the temperature of the pyrolysis furnace was changed to 300, 400, 500, and 600 ° C. Using the obtained powder, a battery was prepared in the same manner as in Example 2, and the characteristics of the positive electrode active material were evaluated. Table 3 shows the results.
Shown in

[0022]

[Table 3]

A battery having a high energy density of 670 Wh / kg or more was obtained with a positive electrode active material having a half width of 0.17 to 0.33 °, but an energy density of a positive electrode active material having a small half width of 0.10 ° was obtained. The value was as low as 420 Wh / kg.

Example 4 Ethanol was added to ammonium metavanadate, and the mixture was ground in a planetary mill for 1, 2, 5, 10 hours. The obtained fine powder of ammonium metavanadate was heat-treated at 600 ° C. for 5 hours and crystallized to obtain V ₂ O ₅ powder. The resulting V ₂
A battery was prepared using O ₅ powder in the same manner as in Example 2, and the characteristics of the positive electrode active material were evaluated. Table 4 shows the results.

[0025]

[Table 4]

With the positive electrode active material having a half width of 0.16 to 0.20 °, a battery having a high energy density of 650 Wh / kg or more was obtained, but the positive electrode active material having a small half width of 0.08 to 0.10 ° was obtained. In this case, the energy density was as low as 370 Wh / kg or less.

[0027]

As described above, according to the present invention,
A positive electrode active material having a high energy density can be prepared, whereby a nonaqueous electrolyte secondary battery having a large charge / discharge capacity can be obtained.

Continued on the front page (72) Inventor Mamoru Mizumoto 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Tatsuo Horiba 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd.Hitachi Laboratory

Claims (2)

(57) [Claims] 1. A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte in which lithium ions are conducted between a negative electrode having lithium as a negative electrode active material and a positive electrode having vanadium pentoxide as a positive electrode active material, The value of X-ray diffraction using vanadium pentoxide using CuKα radiation is the diffraction angle (2θ).
A nonaqueous electrolyte secondary battery, wherein the half width of the diffraction peak on the {200} plane at 15.1 to 15.5 ° is 0.13 ° or more. 2. A positive electrode for a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte in which lithium ions are conducted between a negative electrode having lithium as a negative electrode active material and a positive electrode having vanadium pentoxide as a positive electrode active material. In the evaluation method, the vanadium pentoxide was measured by X-ray diffraction using CuKα radiation, and the half-width value of the diffraction peak on the {200} plane at a diffraction angle (2θ) of 15.1 to 15.5 ° was calculated. A method for evaluating a positive electrode of a non-aqueous electrolyte secondary battery, comprising: comparing a set value set in advance with a value of the half width with respect to the set value.