JP2001351628A - Non-aqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery that has a voltage gradient from the beginning to the completion of charge and discharge period and is improved in the detection precision of the residual capacity from the charge and discharge voltage in a battery which uses lithium titanium oxide in one of the positive electrode and the negative electrode. SOLUTION: The non-aqueous secondary battery is composed of a basic structure of a positive electrode, a negative electrode and a non-aqueous electrolyte and uses a lithium titanium oxide which has a spinel structure and expressed in a general formula Li1+XTi2-XO4 (X=-0.2-1/3) and amorphous in a part of the region in one of the positive electrode and the negative electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a mobile DC power supply,
The present invention relates to a non-aqueous secondary battery used for a backup power supply or the like and using a lithium titanium oxide having a spinel structure for one of a positive electrode and a negative electrode.

[0002]

2. Description of the Related Art With the rapid development of technology in the field of electronics in recent years, electronic devices have been miniaturized, and as a power source for such devices, a secondary of a small, lightweight, chargeable non-aqueous electrolytic system having a high energy density has been developed. There is an increasing demand for batteries, particularly secondary batteries using lithium as an active material. Among these batteries, those using metallic lithium for the negative electrode are most preferable in terms of energy density, but resin-like crystals called dendrites grow on the surface of the lithium negative electrode due to repeated charge and discharge, and the charge and discharge cycle life is extended. It has the disadvantage of being severely impaired. Therefore, a configuration using a material capable of inserting and extracting lithium for the negative electrode has been studied.
As such a negative electrode material, a lithium secondary battery using a metal oxide such as niobium pentoxide or spinel type lithium titanium oxide, a carbon material such as artificial graphite, and a lithium alloy such as a lithium-aluminum alloy has been proposed. ing.

Among the above materials capable of inserting and extracting lithium, spinel-type lithium titanium oxides, especially crystalline ones, can easily occlude and release lithium ions, and have dendrites by repeated charge and discharge. Since there is no occurrence of aging, it is excellent in long-term charge-discharge cycle characteristics. Further, since it has a very flat charge / discharge curve at around 1.5 V with respect to Li / Li ⁺ , a lithium secondary battery using this oxide as a negative electrode has been put to practical use (for example, No. 6-275263). In addition to such application as a negative electrode, spinel-type lithium titanium oxide is characterized by its low charge / discharge potential, and therefore its application as a positive electrode is also being studied. As a negative electrode combined with this positive electrode, Li / Li
Carbon (JP-A-10-64592) and silicon oxide (JP-A-10-162828) having a relatively low potential of 0.5 V or less with respect to ⁺ have been proposed.

[0004]

In a recent electronic device using a secondary battery as a power supply as described above, a function of detecting the remaining capacity of the battery is indispensable. More recently, in order to meet the conflicting demands for higher battery capacity due to increased power consumption on the device side and weight reduction for the purpose of reducing device weight, it is necessary to effectively utilize limited battery capacity. is there.

Therefore, as a method for detecting the discharge capacity of a battery, various methods have been proposed for measuring the charge / discharge current and voltage, and detecting and displaying the battery capacity. However, this method causes an increase in the weight of the electronic device, and is not suitable for a device that emphasizes portability. Therefore, a configuration is adopted in which the relationship between the battery voltage and the remaining capacity is set in a memory in advance, and the remaining capacity is detected from the measured value of the battery voltage.

[0006] The spinel-type lithium titanium oxide comprises:
There is a characteristic that shows a flat potential change at the time of charging and discharging, and shows a sharp potential change at each end of charging and discharging. Therefore, in a battery using lithium titanium oxide for either of the positive and negative electrodes,
It is difficult to detect the remaining capacity in the area where the voltage is flatly displaced due to the small voltage change due to charge and discharge, and in the area where the voltage is rapidly changed, the voltage fluctuates greatly with small changes in the remaining capacity. Therefore, there is a problem that the detection accuracy of the remaining capacity based on the voltage level is reduced.

An object of the present invention is to solve the above-described disadvantages in the detection accuracy of the remaining capacity. It is an object of the present invention to provide a battery using lithium titanium oxide for a period from the initial discharge to the end of discharge. The present invention provides a non-aqueous secondary battery having a voltage gradient and improving detection accuracy of the remaining capacity due to a change in charging voltage.

[0008]

Means for Solving the Problems To solve the above problems, a nonaqueous secondary battery of the present invention has a basic structure of a positive electrode, a negative electrode, and a nonaqueous electrolyte. General formula Li _{1 + X} Ti _2-X O ₄ having spinel structure
(X = −0.2 to ３), and at least a part of the region uses an amorphous lithium titanium oxide.

[0009] The non-aqueous secondary battery of the present invention is of a slope type in which the charge / discharge curve changes the discharge voltage in accordance with the increase / decrease in the remaining capacity, and the accuracy of detecting the remaining capacity by measuring the charge / discharge voltage is improved. Further, the amorphous lithium titanium oxide has good reversibility of charge / discharge because the crystal structure before the amorphization is a spinel type, and the charge / discharge by repeated charge / discharge. There is little change in the curve. For this reason, the detection accuracy can be maintained even in a state where deterioration due to repeated charge and discharge has progressed.

Further, the lithium titanium oxide according to the present invention has a crystal structure in which an amorphous phase alone or a crystalline region and an amorphous phase region coexist. In the spinel-type lithium-titanium oxide having such a crystal structure, the reduction potential starts at around 2 V with respect to Li / Li ^{+, and the} potential decreases to 0.1 V.
It shows a characteristic that proceeds with a gradual change in potential up to around 5 V, and the oxidation reaction slightly rises from the previous potential and shows a characteristic of proceeding in the opposite direction. The reason for exhibiting the characteristics is that the presence of the amorphous lithium titanium oxide in the electrode material causes a reaction in which the product changes uniformly, and the potential always changes due to the potential change of the product accompanying the reaction. A varying homogeneous reaction results. For this reason, it is estimated that a potential gradient showing a gentle S-shape is generated. On the other hand, in the crystalline spinel-type lithium titanium oxide, the reactant and the product coexist, and the proportion of the product increases as the reaction proceeds.
Therefore, the oxidation-reduction reaction proceeds at a constant potential, and shows a flat potential change during charge and discharge.

Therefore, when lithium titanium oxide having a spinel structure including a region composed of an amorphous phase is used as a positive electrode or a negative electrode, if the positive electrode to be combined is an active material having a flat charge / discharge potential, the constructed battery is slow. This shows a charge / discharge curve having a voltage gradient that has an S-shaped shape.

The amorphous phase in the lithium titanium oxide of the present invention has a diffraction peak at an interplanar spacing of 2.50 to 2.54 ° in an X-ray diffraction pattern using CuKα ray, and has a half width of 0.12 °. That is all. In a state where the proportion of the amorphous phase in the electrode material is high, the diffraction peak becomes broad and the half width becomes large. As a result of a detailed study performed by the present inventors, the crystallinity was high when the half width was less than 0.12 ° and the amorphous phase was 2.50 to 2.54 °, which is a characteristic of the spinel-type lithium titanium oxide. , The charge / discharge curve showing the potential gradient corresponding to the accurate detection of the remaining capacity cannot be obtained. On the other hand, when the half width was 0.12 ° or more, the proportion occupied by the amorphous phase increased, and a charge / discharge curve showing an S-shaped potential gradient could be obtained.

As described above, the crystal structure of the lithium titanium oxide having a spinel structure of the present invention can be evaluated from the half width in the diffraction pattern, and the oxidization suitable for obtaining the required battery characteristics is obtained. You can choose things.

[0014]

Embodiments of the present invention will be described below. A specific description will be given based on the embodiment. still,
The following embodiments are examples of the present invention, and do not limit the technical scope of the present invention.

The spinel-type lithium-titanium oxide containing a region composed of an amorphous phase according to the present invention is obtained by mixing a lithium compound with titanium oxide and mixing the mixture with 700 to 100%.
After forming a spinel-type lithium titanium oxide obtained by performing a heat treatment in a temperature range of 0 ° C., it is formed by finely pulverizing with a planetary ball mill. It should be noted that a configuration in which an amorphous phase is formed by using ultra-rapid solidification instead of a planetary ball mill is also possible, and other methods may be used as long as they are lithium titanium oxide having a region composed of an amorphous phase.

The spinel-type lithium titanium oxide of the present invention has the general formula Li _{1 + X} Ti _2-X O ₄ (−0.2 ≦ X ≦ 1 /
It is represented by 3). Among them, a typical composition is L
i _0.8 Ti _2.2 O ₄ , LiTi ₂ O ₄ , Li _4/3 Ti
_5/3 O _{4 and the} like, all of which have good charge / discharge cycle characteristics. In particular, Li _4/3 Ti _5/3 O ₄ is excellent in terms of ease of mass production in addition to charge / discharge cycles and is industrially effective.

(First Embodiment) As a first embodiment, a non-aqueous secondary battery using a lithium titanium oxide having a spinel structure according to the present invention as a positive electrode will be described.

A lithium titanium oxide containing a region composed of an amorphous phase was prepared by the following procedure. First, 4/5 mol of lithium hydroxide was mixed with 1 mol of titanium oxide, and heat-treated at 800 ° C. for 8 hours in an oxygen atmosphere to prepare a spinel-type lithium titanium oxide. This spinel-type lithium titanium oxide is 1, 3 in a planetary ball mill.
Grinding for 5, 10 hours. Table 1 shows the half widths of the diffraction peaks corresponding to the interplanar spacing of 2.50 to 2.54 ° when the ground lithium titanium oxide was measured by X-ray diffraction using CuKα as a target.

[0019]

[Table 1]

As the grinding time increases, the half width increases. 90% by weight of these samples, 5% by weight of acetylene black as a conductive material and 5% by weight of a fluororesin as a binder were kneaded at a weight ratio of 5% by weight, and pellets having a diameter of 15 mm and a thickness of 0.6 mm were obtained. What was molded and dehydrated by vacuum drying at 250 ° C. was used as a positive electrode. Here, the filling amount of lithium titanium oxide was 100 mg.

Next, a flat battery was prepared using the obtained positive electrode. FIG. 1 is a sectional view of the nonaqueous battery according to the present embodiment. In FIG. 1, case 1 also serves as a positive electrode terminal, and is made of stainless steel having a thickness of 0.5 mm. The sealing plate 2 also serves as a negative electrode terminal, and is made of stainless steel having a thickness of 0.5 mm, like the case 1. The gasket 3 made of polypropylene insulates the poly case 1 and the sealing plate 2 and is formed to have a thickness of about 0.3 mm and a substantially L-shaped cross section. The positive electrode 4 is made of the lithium titanium oxide prepared by the above procedure. The negative electrode 5 used metallic lithium.
Metallic lithium sheet is 15mm in diameter and 0.6m in thickness
m, and this was placed on the inner surface of the sealing plate. The separator 6 is a 0.3-mm-thick polypropylene nonwoven fabric. The electrolyte is propylene carbonate (P
LiPF ₆ is dissolved in an equal volume mixed solvent of C), ethylene carbonate (EC) and 1,2-dimethoxyethane (DME) at a ratio of 1 mol / l. The fabricated battery has an outer diameter of 20 mm and a height of 2.0 mm.

Second Embodiment As a second embodiment, a non-aqueous battery using the lithium titanium oxide according to the present invention for a negative electrode will be described.

As in Embodiment 1, titanium oxide and lithium hydroxide were mixed and heat-treated to prepare a spinel type lithium titanium oxide. This is a planetary ball mill, 1, 3,
Pulverization was performed for 5 or 10 hours to obtain a spinel-type lithium titanium oxide having a half width shown in Table 1. 100mg of these
Each was weighed, formed into a pellet having a diameter of 15 mm and a thickness of 0.6 mm, and further subjected to drying and dehydration treatment. Furthermore, these negative electrode pellets were immersed in an electrolytic solution to occlude lithium, thereby obtaining negative electrode pellets.

The positive electrode has a voltage of 3.0 V with respect to Li / Li ⁺ .
Lithium manganese oxide having the following potential was used. 90% by weight of LiMnO ₂ obtained by calcining manganese and lithium, kneading a car, 5% by weight of acetylene black as a conductive material, and 5% by weight of a fluororesin as a binder, and It was formed into a pellet having a diameter of 15 mm and a thickness of 0.6 mm, and was subjected to vacuum drying at 250 ° C. and dehydration treatment.

Using the obtained pellets of the positive electrode and the negative electrode, a flat battery as shown in FIG. 1 was produced. The components other than the pellets are the same as in the first embodiment.

[0026]

EXAMPLES (Example 1) As a first example, evaluation was performed using the battery manufactured in the first embodiment. The positive electrode 4 has a pulverization time of lithium titanium oxide of 0 h, 1
h, 3h, 5h, and 10h were used.
Batteries were prepared for each of these positive electrodes to obtain Batteries A, B, C, D, and E.

In the discharge test, the battery was discharged at a constant current of 1 mA at room temperature, and the discharge sustaining voltage up to 0.5 V is shown in FIG. As apparent from FIG. 2, the voltage gradient of the discharge is increased by increasing the pulverization time, that is, by increasing the half width. A battery with a long pulverization time and a half-value width of 0.12 ° or more, while the battery A without pulverization has a pulverization time of about 2 mV and a battery B with a short pulverization time of about 5 mV per 10% of the discharge capacity. C, D, and E were as large as 50 mV or more, and it was easy to detect the remaining capacity by voltage check.

The reason why the voltage gradient does not change so much even when the ratio of amorphous phase is increased when the half width is 0.12 ° or more is that when the particles are ground using a planetary ball mill, the surface of the particles tends to become amorphous due to friction. If the half width is 0.12 ° or more, it is considered that the particle surface is covered in an amorphous state.

(Example 2) As a second example, evaluation was performed using the battery manufactured in the second embodiment.
The negative electrode 5 has a pulverization time of lithium titanium oxide of 0 h,
h, 3h, 5h, and 10h were used.
Batteries were prepared for each of these negative electrodes to obtain Battery F, Battery G, Battery H, Battery I, and Battery J.

In the discharge test, the battery was discharged at a constant current of 1 mA at room temperature, and the discharge sustaining voltage up to 0.5 V is shown in FIG. As is clear from FIG. 3, batteries H, I, and J having a long pulverization time and a half-value width of 0.12 ° or more as in Example 1.
Has a large voltage gradient, which makes it easier to detect the remaining capacity by voltage check.

Next, FIG. 4 shows that a constant current of 1 mA and 2.5 V
5 shows changes in the discharge capacity of each battery obtained when charging and discharging are repeated between 0.5 and 0.5 V. All of the batteries are stable up to 100 cycles, and the reversibility is not lost even in the presence of amorphous lithium titanium oxide. Lithium ion doping of lithium ion during charging and discharging of lithium titanium oxide crystal,
This is because the undoped reaction scarcely distorts the crystal lattice, but it is considered that the same reason is obtained even when amorphous lithium titanium oxide is present.

[0032]

As is clear from the above embodiments, according to the present invention, a spinel-type lithium titanium oxide in which an amorphous state or an amorphous state and a crystalline state coexist is used as an electrode material, so that the voltage An object of the present invention is to provide a lithium battery electrode material having a voltage gradient from the beginning to the end of discharge to facilitate detection of the remaining capacity and facilitating detection of the remaining capacity by the discharge voltage.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a flat nonaqueous secondary battery according to first and second embodiments.

FIG. 2 is a discharge characteristic diagram in Example 1.

FIG. 3 is a discharge characteristic diagram in Example 2.

FIG. 4 is a diagram showing a charge / discharge cycle and a discharge capacity in Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Case 2 Sealing plate 3 Gasket 4 Positive electrode 5 Negative electrode 6 Separator

Continued on the front page F term (reference) 5H029 AJ03 AK03 AL03 AM03 AM04 AM05 AM07 BJ03 BJ16 DJ16 DJ17 DJ18 HJ02 HJ13 5H050 AA08 BA17 CA07 CB03 EA10 EA24 FA12 FA17 FA19 FA20 GA05 HA02 HA13

Claims (6)

[Claims] 1. A non-aqueous secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte as a basic component, having a general formula Li _{1 + X} Ti _2-X O ₄ (X = −0.2 to A non-aqueous secondary battery characterized by using, as one of the positive electrode and the negative electrode, lithium titanium oxide represented by (1/3) and at least a part of the region is in an amorphous state. 2. The non-aqueous secondary battery according to claim 1, wherein the lithium titanium oxide has a crystalline region and an amorphous region. 3. The non-aqueous secondary battery according to claim 1, wherein the surface layer of the lithium titanium oxide is in an amorphous state. 4. An X-ray diffraction pattern using CuKα radiation, wherein the lithium titanium oxide has an interplanar spacing of 2.50 to 2.5.
The non-aqueous secondary battery according to claim 1, which has a diffraction peak at 4 ° and a half width of 0.12 ° or more. 5. The method according to claim 1, wherein the lithium titanium oxide is Li _4/3 Ti.
Non-aqueous secondary battery of claim 1, wherein a _5/3 O _4. 6. The non-aqueous secondary battery according to claim 1, wherein the amorphous region of lithium titanium oxide is formed by a mechanical pulverization method.