JPH0750166A - Lithium battery - Google Patents

Abstract

PURPOSE:To obtain a lithium battery at a high voltage and a high capacity by setting a ratio of the number of lithium, with which the copper compound oxide of the positive electrode active material reacts per one molecule at the time of discharge, to the number of oxygen included in one molecule of the copper compound oxide, at one or more. CONSTITUTION:Lithium or lithium-containing material is used for a negative electrode 2, and the electrolyte, which is obtained by dissolving LiCF3SO3 and LiClO4 in the mixture organic solvent of ethylene carbonate and 1, 2- dimethoxyethane, is used to form a lithium battery. At this stage, as the active material of a positive electrode 1, copper compound oxide such as Cu3TeO6, which is mainly composed of copper, tellurium and oxygen, is used. Discharge reaction progresses in order of Cu3TeO6+6Li 3Cu+Li6TeO6, and Li/O=6/6=1, and a high capacity can be obtained. Lowering of voltage at the initial time of discharge can be restricted by adding the active material such as TiS2 for lithium secondary battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium battery, and more particularly to improvement of its positive electrode active material.

[0002]

2. Description of the Related Art Hitherto, as a high capacity density lithium battery, a lithium battery using copper oxide as a positive electrode active material (hereinafter abbreviated as Li / CuO) has been proposed [for example, Broussery M. et al. , Jumel
Y, and Cabano J. P. (1977) 15
2nd Electrochemical Society
ty Meeting, Atlanta].

[0003]

However, the above L
i / CuO had a low closed circuit voltage of about 1.5V.

Therefore, an object of the present invention is to provide a high voltage and high capacity lithium battery.

[0005]

Means for Solving the Problems The present invention has achieved the above object by using, as a positive electrode active material in a lithium battery, a copper composite oxide including a compound containing copper, tellurium and oxygen as main component elements. It is a thing.

Examples of compounds containing the above-mentioned main component elements of copper, tellurium and oxygen include Cu3TeO6 and CuTe.
Examples thereof include O3, CuTeO5 and CuTeO4.

The reason why the lithium battery of the present invention has a high capacity is not always clear at present, but it is considered as follows when Cu3TeO6 among the above compounds is taken as an example and explained.

A lithium battery using lithium as a negative electrode and Cu3 TeO6 as a positive electrode active material (hereinafter referred to as Li / C
The discharge reaction of (u3TeO6) is considered to proceed according to the following equation.

Cu3 TeO6 + 6Li → 3Cu + Li6 TeO6

According to the above discharge reaction formula, the number of reacting Li (lithium) is 6 with respect to 6 oxygen atoms.

The volume of the oxide used as the positive electrode active material depends mainly on the volume of oxygen (O), and the discharge capacity is determined by the number of reacting Li.

Therefore, the ratio between the number of lithium and the number of oxygen, that is, Li / O can be used as a criterion for determining whether or not the material is a high capacity material.

Until now, Cu has been used as a positive electrode active material capable of providing a high voltage lithium battery of about 2.0 to 2.5 V.
4O (PO4) 2 has been proposed, but this Cu4O
In the case of (PO4) 2, Li / O = 8/9.

On the other hand, Cu3 Te used in the present invention
O6 is Li / O = 6/6, that is, Li / O = 1, and Li / O is larger than the above Cu4O (PO4) 2, and Cu3TeO6 used in the present invention is the C which has been conventionally proposed.
It can be qualitatively understood that the capacity will be higher than that of u4 O (PO4) 2, and if Li / O is larger than 1, higher capacity can be expected.

Tellurium (Te), which belongs to Group VI of the Periodic Table and is located next to selenium (Se), has much less toxicity than selenium and has a hexavalent valence of tellurium (Te).
6+) is safe to use.

Further, since the atomic weight of tellurium is large, C
u3 TeO6 has a very high density of 6.34 g / cm3 as an oxide and has a capacity density per weight (mAh / g).
In comparison with Cu4 O (PO4) 2, the capacity density per volume (mAh / cm3) is Cu4 O.
It is larger than (PO4) 2, and is very advantageous for increasing the capacity of batteries having a limited internal volume, such as coin-type lithium batteries and cylindrical lithium batteries. Especially in a battery with an internal volume of 5 cm3 or less, Cu3 TeO
It is preferable to have a high density of 6 g / cm 3 or more such as 6.

As a typical example of the copper composite oxide used as the positive electrode active material in the present invention, the main component element is copper,
A compound of tellurium and oxygen can be mentioned, and the main component element means both a component element consisting only of copper, tellurium and oxygen, and a case where a small amount of another element is added to them.

In the compound containing copper, tellurium and oxygen as the main constituent elements, the composition ratio of copper, tellurium and oxygen is 3: 1: 6 in atomic ratio (atomic ratio).
That is, Cu3 TeO6 is particularly preferable because it has a higher Li / O ratio than other copper tellurium complex oxides and has a high safety to the human body.

The lithium battery using these copper complex oxides as the positive electrode active material has the excellent characteristics of high voltage and high capacity as described above, but on the other hand, at the initial stage of discharge, the discharge voltage (closed circuit voltage). ) Is seen to drop. Then, the discharge voltage recovers when about 10% of the discharge capacity is discharged.

The cause of this is not always clear at present, but it is considered to be related to the fact that the copper composite oxide such as Cu3 TeO6 has no electronic conductivity.

This can be solved by adding a positive electrode active material for a lithium secondary battery having a potential range of 2 V or more to lithium to the copper composite oxide of the positive electrode active material.

First, a lithium battery using lithium as the negative electrode and Cu3 TeO6 as the positive electrode active material was prepared.
When the battery is discharged, it shows a discharge voltage of about 2.0 V where the voltage becomes flat, but 1.7 at the initial stage of discharge.
The discharge voltage drops to near V. In addition, this voltage drop occurs again even if the discharge is paused even in a region where the voltage becomes flat.

Therefore, except that TiS2 (titanium disulfide), which can be charged and discharged and has a potential range of 2.5 V to 1.8 V with respect to lithium, was added to Cu3 TeO6 and used as the positive electrode active material. When a lithium battery similar to the above is manufactured and the battery is discharged, TiS2 or the like is discharged where the discharge voltage of Cu3 TeO6 is decreased, so that the voltage drop is suppressed. Then, when the discharge voltage of Cu3 TeO6 recovers to a voltage flat portion of about 2.0 V, the discharged TiS2 or the like is charged again to about 2.0 V.

As a result, the Cu
When the discharge voltage of 3 TeO6 drops, the T
Since iS2 etc. are discharged again, the voltage drop is suppressed.

If only the voltage drop at the initial stage of discharge is suppressed, the positive electrode active material to be added does not necessarily need to be rechargeable, but it is considered to suppress the voltage drop at the time of re-discharge after the discharge is stopped. The positive electrode active material to be added is preferably a rechargeable positive electrode active material for a secondary battery.

In the present invention, as the positive electrode active material for a lithium secondary battery having a potential range of 2 V or more with respect to lithium to be added to a copper complex oxide such as Cu3 TeO6, other than TiS2 described above, for example, MoS2, VS
e, MoS3, Fe0.25V0.75S2, NbSe3 and other chalcogenides, Li2 MoO3, LiMn3 O6 and other lithium composite oxides, V6 O13, amorphous V2
O5 or the like can be used. Such a positive electrode active material for a lithium secondary battery is appropriately selected according to the type of copper complex oxide used and the application of the battery, etc., but chalcogenide is considered to be particularly suitable because it has high electron conductivity. To be

Further, in the positive electrode active material for a lithium secondary battery to be added to a copper composite oxide such as Cu3 TeO6, it is desirable that the potential range with respect to lithium is 2 V or more. Although there are some differences depending on the discharge conditions and the discharge conditions, the voltage drop at the start of discharge is close to 1.7 V, and it is necessary to compensate for this voltage from 1.7 V to the flat part voltage (about 2.0 V). It is a thing. Further, as is clear from this reason, as the positive electrode active material for the lithium secondary battery to be added,
Those having a large capacity between 1.7 and 2.0 V are particularly preferable.

Cu3TeO, which is a positive electrode active material for a lithium secondary battery having a potential range of 2 V or more with respect to these lithium
The amount of 6 or the like added to the copper complex oxide is not particularly limited, but the positive electrode active material for a lithium secondary battery having a potential range of 2 V or more with respect to the above lithium is Cu3 Te.
It is preferable that the total amount with the copper complex oxide such as O6 is 2 to 30% by weight.

The copper composite oxide used as the positive electrode active material in the present invention is capable of obtaining a high capacity lithium battery. The discharge capacity thereof will be described below.
The theoretical discharge capacity of eO6 is 388 mAh / g, the theoretical discharge capacity of TiS2 is 240 mAh / g, and the discharge capacity of Cu3 TeO6 per unit weight is TiS.
This is equivalent to 1.6 times 2 2.

As the copper composite oxide which can obtain the above voltage drop preventing effect by adding the positive electrode active material for lithium secondary batteries having a potential range of 2 V or more with respect to lithium as described above, In addition to the above Cu3TeO6, CuTeO3, CuTeO5, CuTeO4, Cu
GeO3, Cu2 GeO4, Cu3 B2 O6, Cu2 P
2 O7, Cu3 P2 O3, Cu4 P2 O9, Cu5 P2
O10, Cu2 V2 O7, Cu3 WO6, Cu3 TiO5
, Cu2 MgO3 and the like. Since these copper complex oxides have different voltages and discharge capacities, they can be appropriately used according to the required characteristics of the battery and the intended use.

The positive electrode is made of the above-mentioned copper composite oxide, if necessary.
A positive electrode active material for a lithium secondary battery having a potential range of 2 V or more with respect to lithium added thereto, and further, an electron conduction aid such as acetylene black or graphite or polytetrafluoroethylene or the like. It is prepared by adding and mixing a different binder and molding the obtained positive electrode mixture by an appropriate means. Also, TiS2,
When MoS2 having electron conductivity is added, the electron conduction aid can be omitted.

In the battery of the present invention, lithium or a lithium-containing substance such as a lithium alloy such as a lithium-aluminum alloy or lithium-carbon is used for the negative electrode, and is appropriately used according to the required characteristics of the battery and its application. Can be divided. In addition, in order to improve the storability, the capacity of the negative electrode may be smaller than the capacity of the positive electrode active material, and thus the battery may be a negative electrode regulated battery.

As the electrolytic solution, for example, LiCF3 SO
2, LiClO4, LiPF6, LiBF4, LiC4
One or more electrolytes such as F9 SO3
What was dissolved in an organic solvent such as 2-dimethoxyethane, 1,2-diethoxyethane, propylene carbonate, ethylene carbonate, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, diethyl carbonate, or a mixed solvent of two or more kinds. Is used and is appropriately selected according to the required characteristics of the battery and its application.

[0034]

EXAMPLES Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to only those examples.

Example 1 First, Cu3 TeO6 was synthesized as follows.

Copper oxide (CuO) and telluric acid (H6 TeO)
6) and 3) were mixed at a molar ratio of 3: 1, and the obtained mixture was heated in air at 700 ° C. for 36 hours to obtain a light yellow-green substance.

The material obtained had a particle size of about 1 μm and was confirmed to be Cu3 TeO6 by powder X-ray diffraction. For the powder X-ray diffraction measurement, CuKα ray was used and the applied voltage was 50 k.
2θ = 10 ° to 100 ° with an X-ray source of V and current of 150 mA
Was measured. The results are shown in the upper part of FIG.

Further, instead of copper oxide, copper carbonate [CuCO3
.Cu (OH) 2 .H2 O] was used to react with telluric acid (H6 TeO6) in the same manner as above, and a light yellow-green substance was obtained in the same manner as above. This material was confirmed to be Cu3TeO6 by powder X-ray diffraction analysis similar to the above.

Cu obtained by using this copper carbonate as a starting material
An X-ray diffraction image of 3 TeO 6 is shown in the lower part of FIG.

As is clear from FIG. 2, copper oxide (Cu
O3) as a starting material, and Cu3TeO6 obtained by using copper carbonate [CuCO3.Cu (OH) 2 .H2O] as a starting material, although some peak intensity ratios are different, The same X-ray diffraction image is shown in Fig. 1, and it can be seen that they are all Cu3 TeO6.

Of the above-mentioned Cu3TeO6, Cu3TeO6 obtained by using CuO as a starting material is used as a main agent.
% By weight, and CuGeO3, Cu3 WO6 as auxiliary agents,
Cu3 TiO5 and Cu2 MgO3 were added to and mixed with 3.5% by weight, 0.5% by weight, 0.5% by weight and 0.5% by weight, respectively, to obtain a main component of the positive electrode active material. The main component of the positive electrode active material was weighed out in an amount corresponding to 85% by weight, and 15% by weight of the following additives were added thereto and mixed to use as a positive electrode active material. As the above-mentioned additive, the above-mentioned TiS
90% by weight of 2 as the main agent, MoS2 as the auxiliary agent,
LiMn3 O6 was used by adding 5 wt% and 5 wt% of each and mixing. Table 1 shows the respective weight ratios.

[0042]

[Table 1]

In the positive electrode active material shown in Table 1 above, a mixture of flaky graphite and acetylene black in a weight ratio of 1: 1 as an electron conduction aid and polytetrafluoroethylene as a binder in a ratio of 80: 18: 2 ( A weight ratio) was mixed to prepare a positive electrode mixture.

60 mg of this positive electrode mixture was filled in a mold,
A disk having a diameter of 10 mm was pressure-molded at a pressure of 1 t / cm2, pelletized to about 4 g / cm3, and then heat-treated at 250 ° C to form a positive electrode. The positive electrode was used to form a button having the structure shown in Fig. 1. A lithium battery was manufactured.

In FIG. 1, 1 is the above positive electrode, and 2
Is a negative electrode made of disc-shaped lithium having a diameter of 14 mm. 3 is a separator made of polypropylene non-woven fabric, 4 is a positive electrode can made of stainless steel, 5 is a positive electrode current collector made of stainless steel net, and 6 is a negative electrode can made of stainless steel and having a surface plated with nickel. .

Reference numeral 7 denotes a negative electrode current collector made of stainless steel net, which is spot-welded to the inner surface of the negative electrode can 6. The negative electrode 2 is pressure-bonded to the negative electrode current collector 7 made of stainless steel net. Has been done. Numeral 8 is a polypropylene annular gasket, and in this battery, LiCF3 SO3 and LiClO4 were added to 0.5 m each in a mixed solvent of ethylene carbonate and 1,2-dimethoxyethane in a volume ratio of 1: 1.
An electrolytic solution in which ol / l and 0.1 mol / l are dissolved is injected. The injection amount was such that the ratio of the amount of electrolytic solution (μl) / the discharge capacity of the positive electrode active material (mAh) was 0.9.

Example 2 The amount of the additive shown in Table 1 containing TiS2 as the main component and added to the main component of the positive electrode active material shown in Table 1 containing Cu3 TeO6 as the main component was set to 5% by weight based on the total amount of them. A lithium battery was manufactured in the same manner as in Example 1. That is, the composition of the positive electrode active material in the lithium battery of Example 2 was C
The main component of the positive electrode active material shown in Table 1 containing u3 TeO6 as the main component was 95% by weight, and the additive shown in Table 1 containing TiS2 as the main component was 5% by weight.

Example 3 A lithium battery was prepared in the same manner as in Example 1 except that the positive electrode active material containing Cu3 TeO6 as a main component was not added with the additives shown in Table 1 such as TiS2. It was made.

Comparative Example 1 A lithium battery was produced in the same manner as in Example 1 except that the positive electrode active material was changed to copper oxide (CuO).

Comparative Example 2 A lithium battery was manufactured in the same manner as in Example 1 except that the positive electrode active material was changed to Cu4 O (PO4) 2.

Next, the batteries of Examples 1 to 3 and Comparative Examples 1 and 2 were discharged at a discharge current of 0.85 mA,
The discharge characteristics were investigated. The discharge curve of each battery is shown in Fig. 3,
This is shown in FIGS. 3 to 5, the vertical axis represents voltage and the horizontal axis represents capacity density per unit weight (mAh / g).

The capacity density per unit weight when the discharge final voltage is 1.5 V of each battery is 370 to 390 mAh / g in Examples 1 to 3 as shown in FIG. 3, and in Comparative Example 1 as shown in FIG. Is 110 mAh / g, and Comparative Example 2 is 400 mAh / g as shown in FIG.

When this is shown as a positive electrode active material, the capacity density when the discharge end voltage is 1.5 V is Cu shown in Table 1.
Copper complex oxide containing 3 TeO 6 as a main component (in the case of Example 3) is 390 mAh / g, CuO is 110 mAh / g,
Cu4 O (PO4) 2 is 400 mAh / g.

CuO having a low voltage has a discharge end voltage of 1.5.
When V is set, the capacity density is reduced, but C used in the present invention is
u3 TeO6 had the same level of capacity density per unit weight as Cu4 O (PO4) 2.

However, the specific gravity of each is Cu3 T
eO6 is 6.34 g / cm3, Cu4 O (PO4) 2
Is 4.54 g / cm3, and the capacity density (mAh / cm3) per unit volume of both is calculated as Cu3
TeO6 is 2400 mAh / cm3, and Cu4 O (PO
4) 2 becomes 1900 mAh / cm3, and Cu3 TeO
6 has a larger capacity density per unit volume than Cu4 O (PO4) 2.

Since the battery size of a practical battery is determined, the internal volume that can be filled with the active material is also practically limited. Therefore, in order to increase the capacity, the capacity density per unit volume is large. An active material is necessary, and from this aspect Cu
It can be said that 3 TeO 6 is a highly useful material as a positive electrode active material.

In order to obtain a high capacity of 250 mAh / cm3 or more, especially in a battery having a limited internal volume of 5 cm3 or less, 2000 mAh / cm3 such as Cu3TeO6 is required.
The above materials are preferable.

FIG. 6 is a diagram showing the discharge characteristics of the batteries of Examples 1 to 3 at the beginning of discharge. As is clear from the results shown in FIG. 6, the copper composite containing Cu3 TeO6 as the main component was used. In the battery of Example 3 in which the oxide was used alone, a voltage drop was observed in the region from the start of discharge to the portion corresponding to about 10% of the discharge capacity. In particular, the voltage dropped to near 1.7 V at the start of discharge.

On the other hand, in the battery of Example 1 in which the positive electrode active material for lithium secondary battery containing TiS2 as the main component was added to the copper composite oxide containing Cu3TeO6 as the main component in an amount of 15% by weight in the total amount, No voltage drop observed in the battery No. 3 was observed, and the discharge characteristics were almost flat.
In addition, Cu3TeO6 is used as a main component in a copper composite oxide containing Ti.
Even in the battery of Example 2 in which the positive electrode active material for a lithium secondary battery containing S2 as a main component was added in an amount of 5% by weight based on the total amount thereof, the voltage drop at the start of discharge as observed in the battery of Example 3 was not observed. The discharge characteristics were almost flat.

In applications where the current density is 1 mA / cm 2 or more and discharge current is used, and in applications where the temperature is 0 ° C. or less, the voltage drop at the beginning of discharge tends to be large. It is preferable to add 10 to 30% by weight of a positive electrode active material for lithium secondary batteries. Other than that, it is preferable to add the additive in an amount of 2 to 10% by weight, as in Example 2.

The amount of the electrolytic solution to be injected is the amount of the electrolytic solution (μ
1) / the discharge capacity (mAh) ratio of the positive electrode active material is 0.8 to
It is preferably set to 1.5. And Cu3
In order to obtain a high-density pellet using a material having a high specific gravity of 6 g / cm3 or more such as TeO6, the electron conduction aid mixed with the pellet is preferably 2 to 25% by weight of the positive electrode mixture. Further, the binder is preferably 0.2 to 5% by weight. The amount of the electron conduction aid is determined by the electron conductivity and the surface state of the positive electrode active material main component (here, Cu3 TeO6 is the main component) used, and the amount of the binder is also the positive electrode active material main component. The optimum amount is determined by the specific gravity and particle size of.

In an actual battery, it is preferable that the amount of lithium in the negative electrode is regulated to be smaller than the discharge capacity of the positive electrode. That is, at the end of discharge, the hexavalent tellurium may have a low valence due to the reaction with lithium, and the low valence may adversely affect the storability due to the reaction with the electrolytic solution. . Cu3
TeO6 has a flat voltage region near 2 V (vs. Li), and then gradually decreases to a voltage near 1 V. Specifically, it is preferable that the amount of lithium in the negative electrode is limited to the amount of electricity in this flat region only, so that the positive electrode and lithium do not react thereafter.

[0063]

As described above, according to the present invention,
A high-voltage and high-capacity lithium battery can be provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a lithium battery according to the present invention.

FIG. 2 Cu3 used as a positive electrode active material in the present invention
It is a figure which shows the X-ray-diffraction image of TeO6.

FIG. 3 is a discharge characteristic diagram of the batteries of Examples 1 to 3.

FIG. 4 is a discharge characteristic diagram of the battery of Comparative Example 1.

5 is a discharge characteristic diagram of the battery of Comparative Example 2. FIG.

FIG. 6 is a discharge characteristic diagram at the start of discharge of the batteries of Examples 1 to 3.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode 3 Separator

Claims (6)

[Claims] 1. A lithium battery using lithium or a lithium-containing substance as a negative electrode, a copper composite oxide as a positive electrode active material, and an organic solvent-based electrolyte solution, wherein the copper complex oxide per molecule is discharged. Lithium (L
Li / O, which is the ratio of the number of i) to the number of oxygen (O) contained in one molecule of the above copper composite oxide, is 1 or more, a lithium battery. 2. The lithium battery according to claim 1, wherein
A lithium battery characterized in that a compound containing copper, tellurium and oxygen as main components is used as a copper complex oxide. 3. A lithium battery in which the compound containing copper, tellurium and oxygen as a main component according to claim 2 is Cu3 TeO6. 4. The copper complex oxide according to claim 1, wherein the copper composite oxide is at least CuGeO3, Cu3 TiO4, Cu3 WO6.
, Cu2 MoO5, Cu2 MgO3. 5. The lithium battery according to claim 1, wherein a positive electrode active material for a lithium secondary battery having a potential range of 2 V or more with respect to lithium is added to the copper composite oxide. 6. The positive electrode active material for a lithium secondary battery is at least TiC2 or MoS2 chalcogenide, and the addition amount thereof is 2 to 30 in the total amount with the copper composite oxide.
The lithium battery according to claim 5, wherein the lithium battery is in weight%.