JPH0650635B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery, and provides an inexpensive secondary battery having excellent cycle characteristics.

_2. Description of the Related Art Conventionally, a non-aqueous electrolyte secondary battery using metallic lithium for a negative electrode and titanium disulfide (hereinafter abbreviated as TiS ₂ ) for a positive electrode has been studied (Japanese Patent Laid-Open No. 50-54836). However, the cycle characteristics of this battery are poor, and it has been considered that this is due to dendrites generated when the lithium of the negative electrode is charged. In fact, the charging and discharging behavior of the positive electrode TiS ₂
When measured on a lithium reference electrode, its cycle characteristics were excellent.

In order to solve this problem of the negative electrode, it has been considered to use an alloy containing 63 to 92% of lithium in the number of atoms and the balance being aluminum for the negative electrode, and use TiS ₂ for the positive electrode. 52-5423). This is because the lithium in the lithium aluminum alloy was dissolved in the electrolyte due to discharge, and during charging, lithium formed an alloy with aluminum and was taken into the negative electrode. Therefore, it is obvious that the greater the amount of lithium in the alloy, the greater the amount of electricity, which is advantageous.

On the other hand, since TiS ₂ is expensive, a battery using manganese dioxide (hereinafter abbreviated as MnO ₂ ) as the positive electrode active material and metallic lithium as the negative electrode was considered. However, this battery also had poor cycle characteristics. Therefore, attempts have been made to improve the negative electrode.
That is, using a lead-lithium alloy for the negative electrode, the lithium in the lead-lithium alloy is dissolved in the electrolyte by discharge, and a lead-lithium alloy is produced by discharge (JP-A-57-1).
No. 41869). Furthermore, cuprous oxide (hereinafter
It has also been proposed to use an electrolytic reduction product of lithium (Cu ₂ O) for the negative electrode (Japanese Patent Application Laid-Open No. 55-166871).

Problems to be Solved by the Invention In a secondary battery using TiS ₂ as a positive electrode and a lithium aluminum alloy as a negative electrode, the problem of dendrite of the negative electrode was solved, and the battery had good cycle characteristics.

On the other hand, the battery using inexpensive MnO ₂ for the positive electrode and the lithium lead alloy for the negative electrode is improved over the battery using negative electrode of metallic lithium, but the cycle characteristics are not sufficient. In the negative electrode using this lithium lead alloy, the problem of dendrite has been solved, and the deterioration has occurred in the positive electrode.

However, in the battery using the electrolytic reduction product of Cu ₂ O for the negative electrode and MnO ₂ for the positive electrode, the cycle characteristics were good, the problem of dendrite of the negative electrode was solved, and the cycle characteristics of the positive electrode were also good. However, the voltage of this battery has a low defect of 2V to 1V because the electrolytic reduction product of Cu ₂ O is used for the negative electrode.

From the above, in the non-aqueous electrolyte battery using MnO ₂ for the positive electrode, it is not enough to simply solve the problem of dendrite on the negative electrode, and it can be estimated that the cycle characteristics change considerably depending on the substance used for the negative electrode.

The present invention is a high voltage, in a non-aqueous electrolyte secondary battery using inexpensive MnO ₂ for the positive electrode, the cause of reducing the cycle characteristics is considered, the negative electrode having a specific composition is proposed, and the cycle characteristics of the secondary battery are considered. Is to improve.

Means for Solving the Problems In the present invention, in a non-aqueous electrolyte secondary battery using MnO ₂ for the positive electrode, lithium is used for the negative electrode in a percentage of the number of atoms of 5 to 60%.
By using the contained lithium aluminum alloy, it is possible to obtain a high-voltage secondary battery having excellent cycle characteristics.

Action As described above, in the non-aqueous electrolyte secondary battery using MnO ₂ as a positive electrode, even if the problem of dendrite of the negative electrode is solved, deterioration occurs in the positive electrode and the cycle characteristics are poor.

The present inventors studied as described in the section of Examples and considered as follows. That is, when repeating charging and discharging,
Precipitated metal lithium, which is the negative electrode, or lithium in the lithium-lead alloy and the solvent used for the electrolyte undergo a chemical reaction, and this reaction product, for example carbon dioxide, diffuses into the electrolyte and is adsorbed or reacted on the positive electrode. However, it is considered that this deteriorates the cycle characteristics of the positive electrode.

In order to solve this problem, it is necessary to suppress the reaction between the electrolyte and the negative electrode. As a result of examining various negative electrodes, the present inventors have found that a lithium aluminum alloy having a percentage of the number of lithium atoms of 5 to 60% is preferable. From the viewpoint of energy density, the larger the amount of lithium in the lithium aluminum alloy, the better. However, the amount of lithium is 60
If it exceeds%, the reaction of the electrolyte similar to that of the lithium-lead alloy becomes remarkable, and the cycle characteristics of the battery deteriorate. Therefore, 60% or less, preferably 50% or less is good.

From the viewpoint of energy density, the amount of lithium is 5% or more, preferably 10% or more.

Example <Example 1> Using the electrochemical cell shown in FIG. 5, the cycle characteristics of MnO ₂ as a positive electrode were examined. In the figure, 1 is a positive electrode and 250 in air
A mixture consisting of 70 parts by weight of MnO ₂ heated to ℃, 15 parts by weight of acetylene black as a conductive agent, and 15 parts by weight of polytetrafluoroethylene resin as a binder is 2 cm x 2 cm and has a thickness of 0.8 mm. It is press molded. Reference numeral 2 is a lead made of a titanium ribbon of a positive electrode, 3 is an electrolyte made of propylene carbonate (hereinafter abbreviated as PC) in which 1 mol / liter of lithium perchlorate (LiClO ₄ ) is dissolved, 4 is a liquid bridge, and 5 is a reference electrode. It is a certain metallic lithium, and 6 is a lead made of a nickel ribbon. 7 is 2 cm using various materials
It is a negative electrode having a size of 2 cm and a thickness of 0.5 mm. Reference numeral 8 is a lead of the negative electrode, which is made of a nickel ribbon.

A battery a using lithium that has been conventionally used for the negative electrode 7 and a battery b using a lithium lead alloy in which the percentage of the number of lithium atoms are 80% are compared with a positive electrode whose potential is 1 relative to the lithium reference electrode. It was discharged at 4 mA until it reached 0.5 V, and then charged at 4 mA until it reached 3.7 V. And then
This discharge and charge were repeated. FIG. 1 shows the change in the discharge amount with the cycle at this time. Further, the results of the battery c using a lithium aluminum alloy composed of 50% lithium as the negative electrode of the present invention are also shown.

In this experiment, the potential of the positive electrode is measured with respect to the lithium reference electrode to regulate charging / discharging. Therefore, the same result must be obtained regardless of the type of the negative electrode. However, as shown in FIG. 1, due to the difference in the negative electrode,
The characteristics of the positive electrode have changed. This was considered to be because a chemical reaction occurred as a side reaction in the negative electrode during charge / discharge, and this reaction product affected the positive electrode. Therefore, PC, which is the solvent of the electrolyte, reacts with lithium and lithium in the lithium-lead alloy to form insoluble lithium carbonate (Li ₂ CO ₃ ) in PC, which decomposes according to the following equation and is soluble in PC. It was considered that carbon dioxide gas (CO ₂ ) Li ₂ CO ₃ → Li ₂ O + CO ₂ was produced, and this CO ₂ diffused in the electrolyte and was adsorbed or reacted on the surface of the positive electrode, which deteriorated the cycle characteristics of the positive electrode. In the lithium aluminum alloy of the present invention, it was considered that the reaction with PC was suppressed and the cycle characteristics were improved.

Next, using the negative electrode used in the battery c of one example of the present invention,
FIG. 1 shows the characteristic results of the battery d using an electrolyte in which CO ₂ was introduced into the electrolyte from the outside and bubbles were generated to saturate the CO ₂ in the electrolyte. From this, it can be seen that the above estimation is valid.

Even if the solvent of the non-aqueous electrolyte is changed to dioxolane or tetrahydrofuran, the electrolyte is also changed to lithium borofluoride (LiB
The same results as in FIG. 1 were obtained even when γ-butyrolactone in which F ₄ ) was dissolved, dimethoxyethane and a mixture thereof were used. It can be seen that even when these electrolytes are used, the electrolyte reacts with lithium or lithium in the lithium-lead alloy, and the reaction product affects the positive electrode, thereby deteriorating the cycle characteristics of the positive electrode.

Example 2 In the same manner as in Example 1, lithium-aluminum alloys having different lithium contents were used for the negative electrode, and the effect of the lithium content in the alloy on MnO ₂ of the positive electrode was examined. FIG. 2 is a graph in which the number of cycles at which the amount of discharge is half the amount of discharge in the second cycle is taken as a reference and the cycle characteristic is plotted against the% of lithium in the negative electrode alloy. From this, it is understood that when the amount of lithium in the lithium aluminum alloy exceeds 60%, the cycle characteristics of the positive electrode are significantly deteriorated. That is, it is shown that when the amount of lithium exceeds 60%, it tends to react with the electrolyte during charge and discharge. From this, lithium is 60% or less,
It is preferably 50% or less.

However, if the amount of lithium in the lithium-aluminum alloy decreases, it leads to a decrease in the amount of discharge of the negative electrode. Therefore, lithium is required to be 5% or more, preferably 10% or more.

<Example 3> Since the deterioration of the cycle characteristics of MnO _{2 in} the positive electrode is due to the reaction product in the negative electrode, the degree of the influence varies depending on the property of manganese dioxide. In the same manner as described in Example 1, a lithium aluminum alloy containing 50% lithium was used for the negative electrode, and MnO ₂ for the positive electrode was compared with one that was heat-treated in the air for 5 hours while changing the temperature.

FIG. 3 is a plot of the heating temperature and the cycle characteristics of the positive electrode. From this, from the viewpoint of cycle characteristics, MnO ₂ heated to 150 ° C. to 400 ° C., particularly 200 to 350 ° C. It was found that it showed good characteristics.
From FIG. 3, it can be seen that the cycle characteristics are good even with MnO ₂ which has not been heat-treated. This indicates that the water content in MnO ₂ does not become a major deterioration factor from the viewpoint of cycle characteristics.

In lithium and manganese dioxide primary batteries, it is said that heat treatment of MnO ₂ of the positive electrode to remove water in MnO ₂ is necessary for improving storage characteristics. However, from the viewpoint of cycle characteristics, heat treatment is better, but it is not a remarkable effect like the storage characteristics of the primary battery. Water in MnO ₂ affects the negative electrode in the storage characteristics of the primary battery, whereas the cycle characteristics of the secondary battery differ in the mechanism of action in which the reaction product of the negative electrode affects the positive electrode. I think it is because Further, in FIG. 4e, MnO ₂ heated at 250 ° C. is used, and the alloy of the present invention containing 50% lithium is used for the negative electrode.
The discharge curve in the 10th cycle in a 3 mm and 2.0 m high battery is shown.

As a result, the average discharge voltage was considerably high at 2.5 V, and compared with the case where the conventional electrolytic reduction product of Cu ₂ O was used for the negative electrode in a battery of the same size, a battery with higher electromotive force could be obtained. it is obvious.

Further, in the conventional secondary battery using TiS ₂ as the positive electrode, as described above, if only the problem of the dendrite of the negative electrode is solved, a secondary battery with good cycle characteristics is obtained, and the MnO ₂ used in the present invention is used. Unlike the above, it is an excellent active material that is not affected by the reaction product at the negative electrode, but it has the drawback of being expensive.

EFFECTS OF THE INVENTION As described above, in a non-aqueous electrolyte secondary battery using MnO ₂ for the positive electrode, by using a lithium aluminum alloy containing 5 to 60% lithium for the negative electrode, a secondary battery with good cycle characteristics is obtained. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing characteristics of a positive electrode when various negative electrodes are used,
Fig. 2 is a diagram plotting the cycle characteristics of the positive electrode when the percentage of lithium in the lithium-aluminum alloy of the negative electrode is changed, and Fig. 3 is a graph when the heating temperature of MnO ₂ is changed using the negative electrode of the present invention. FIG. 4 is a cycle characteristic diagram of the positive electrode, FIG. 4 is a discharge curve of the battery, and FIG. 5 is a vertical sectional view of the cell. a ... Conventional battery using lithium as the negative electrode, b ... Battery using lithium lead alloy as the negative electrode, c ... Battery of the embodiment of the present invention using lithium aluminum alloy as the negative electrode, d ... Battery c
Batteries in which CO ₂ is aerated in the electrolyte at e ... Battery c
A battery using MnO ₂ heat-treated at 250 ° C.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Yamaura 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Toru Matsui, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 56) References JP-A-52-5423 (JP, A) JP-A-59-112569 (JP, A) JP-A-59-94366 (JP, A) JP-A-58-133786 (JP, A)

Claims (2)

[Claims] 1. A non-aqueous electrolyte containing lithium ions, manganese dioxide as a positive electrode active material, and an alloy as a negative electrode composed of 5 to 60% lithium and 95 to 40% aluminum as a percentage of the number of atoms. A non-aqueous electrolyte secondary battery characterized by being used. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the manganese dioxide is manganese dioxide heated to 150 to 400 ° C.