JP3111324B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is a non-aqueous electrolyte secondary battery BACKGROUND OF THE, especially composite oxide of lithium and cobalt (LiCoO ₂₎
And a battery using a carbonaceous material for a negative electrode.

[0002]

2. Description of the Related Art In recent years, portable and cordless electronic devices have been rapidly advancing, and there is a high demand for a small and lightweight secondary battery having a high energy density as a drive power source for these devices. In this respect, non-aqueous secondary batteries, especially lithium secondary batteries, are expected to have high voltage and high energy density.

In particular, recently, a battery system using LiCoO ₂ as a positive electrode active material and a carbon material as a negative electrode has attracted attention as a high energy density lithium secondary battery. The features of this battery system are that the battery voltage is high (because LiCoO ₂ has a high voltage of 4 V with respect to Li) and that the positive and negative electrodes both use an intercalation reaction. In particular, since metal Li is not used for the negative electrode, there is no short circuit due to precipitation of dendritic Li, and safety and rapid charging can be expected.

[0004] Generally, it is basically demanded that this type of secondary battery has a high output, a high capacity and a long service life. However, with the recent advancement of functions of electronic equipment, equipment has been used. Even in the absence of such a device, power consumption by memory backup and control of other control circuits has increased.
That is, if the battery is left attached to the device, the battery continues to be discharged, the capacity runs out, and the battery voltage finally reaches 0V. Therefore, a battery is of low practicality unless it is recovered by recharging after experiencing such discharge (called overdischarge). However, in the case of a lithium secondary battery using LiCoO ₂ for the positive electrode and a carbonaceous material for the negative electrode, if such overdischarge is performed, the original capacity is not restored even if the battery is charged and discharged again, and the battery capacity is reduced. There was a drawback that it became lower. As measures against overdischarge in this battery system, JP-A-63-228573 and JP-A-63-314778 disclose means for adding an oxide such as MoO ₃ , V ₂ O ₅ , and TiO ₂ to the positive electrode. But,
In the case of this battery system, the Li source is only LiCoO ₂ ,
It has been pointed out that since a part of Li contributing to charge and discharge is consumed by the added substance, the charge and discharge capacity is reduced and the effect of suppressing overdischarge deterioration is not so large.
Therefore, as an improved form, Japanese Patent Application Laid-Open No. 2-265
167 discloses means for adding Li _x MoO ₃ or the like already containing Li as a sub-active material to the positive electrode. As a result of examining the effect of this means, a portion of Li contributing to charging and discharging already containing Li is not consumed by the added substance, and the effect of suppressing over-discharge deterioration is great. there were. However, as a result of further study, the effect was surely excellent near room temperature (20 ° C. to 30 ° C.). However, when overdischarge was performed in a high temperature environment, for example, at 60 ° C., the battery was charged and discharged again. However, the battery capacity was not restored to the original capacity, and the battery capacity was reduced. In fact, over-discharge leaving the device mounted may not only be near room temperature but also at high temperatures, so it is necessary to take some measures to prevent over-discharge deterioration even in this case. Can be

[0005] Then, a lithium secondary battery made of a positive electrode made of LiCoO ₂ , a negative electrode made of a carbonaceous material, and an organic electrolyte was prototyped, charged and discharged, and then over-discharged by connecting a resistor. Then, the unipolar behavior of each of the positive and negative electrodes at that time is represented by Li
As a result, when the battery voltage reached 0 V, as shown in FIG.
It turned out that the potential reached near. This means that the potential is controlled by the positive electrode when the positive and negative electrodes become equipotential (the battery voltage becomes 0 V). The positive electrode is usually used at a potential in the vicinity of this, and is 1 to Li.
It is said that there is no loss of reversibility even if the battery is discharged to near V, so it is considered that there is no problem. On the other hand, the negative electrode is usually used at a potential of 1 V or less with respect to Li. That is, it is considered that there is a problem that the potential of the negative electrode is maintained at such a very noble potential due to overdischarge. For example, Japanese Patent Application Laid-Open No. 2-265167 points out that the negative electrode has such a noble potential so that the negative electrode current collector is dissolved to cause deterioration. Therefore, the relationship between the potential of the negative electrode and the performance degradation was examined by the constant potential step method.
It was found that the capacity characteristics of the negative electrode were significantly degraded when it exceeded. Accordingly, when the positive and negative electrodes become equipotential (battery voltage becomes 0 V), the equilibrium potential of the positive electrode that controls the potential is maintained at a lower potential (3 V or less) to suppress overdischarge deterioration. Is the gist of JP-A-2-265167,
The added secondary active material is preferably a Li compound containing Li in advance in order to minimize the loss of Li. By using this means, it was possible to suppress the potential at the time of overdischarge and to suppress the deterioration of the capacity characteristics of the negative electrode. However, this effect is effective only near room temperature, for example, in an environment of 60 ° C. When the overdischarge was carried out, the deterioration of the capacity characteristic was also observed after the overdischarge. Therefore,
The conventional means for controlling the potential alone is not sufficient as a measure against overdischarge at high temperatures. Therefore, as a result of an investigation for investigating the cause of the overdischarge deterioration in a high-temperature environment, it was found that the electrolytic solution was decomposed. Further, as a result of examining the decomposition reaction of this electrolytic solution, it was found that the reaction occurred on the surface of the positive electrode, and it was found that this reaction could occur even if the potential was controlled by conventional means. Considering that there is no charge transfer between the positive electrode and the negative electrode when the voltage reaches 0 V due to overdischarge, there is a strong possibility that this high-temperature overdischarge deterioration is a side reaction that occurs solely on the positive electrode surface. In general, it is said that a Co oxide such as LiCoO ₂ as an active material is a strong oxidation catalyst for organic substances. In particular, such catalytic reaction activity is considered to be promoted in a high-temperature environment.Thus, at the time of over-discharge at high temperature, the catalytic decomposition reaction of the organic electrolyte occurs as a side reaction, resulting in over-discharge deterioration. It is expected to be the cause. Therefore, recovery of an overdischarged secondary battery particularly at a high temperature has a difficult technical problem.

[0006]

The conventional problem to be solved by the present invention is, as described above, a high temperature, for example, 60 ° C.
Secondary battery using a non-aqueous electrolyte that has been over-discharged in the above environment, the original battery capacity cannot be maintained even when the battery is charged and discharged again, that is, the over-discharge deterioration at high temperatures cannot be suppressed. It is.

[0007]

SUMMARY OF THE INVENTION The present invention provides LiCoO ₂
In a non-aqueous electrolyte secondary battery using a positive electrode as a positive electrode active material and a negative electrode using a carbonaceous material as a negative electrode material, in order to solve the above-described problems, a group of Nb, As, Sb, and Bi is used. Secondary composite oxide of at least one selected metal and Li
LiCoO ₂ becomes a solid solution in the battery reaction system
Without being present as a mixture . Further, the positive electrode contains a Li-containing oxide having a discharge potential of 3 V or less with respect to Li, and is a mixture of at least one metal oxide selected from the above group.
You.

[0008]

The present invention is characterized in that a metal compound selected from the group consisting of Nb, As, Sb and Bi is added to the positive electrode, and these compounds suppress the oxidation catalytic activity of the Co oxide against organic substances. It acts as a catalyst poison. By using these compounds in addition to actually controlling the potential, the result was that high-temperature overdischarge deterioration could be suppressed. From this, it is clear that one cause of the overdischarge deterioration at high temperature is the catalytic decomposition reaction of the electrolytic solution, and the means of the present invention aimed at suppressing this reaction is an extremely effective means. . Therefore, in order to suppress over-discharge deterioration, the positive electrode contains a sub-active material having a discharge potential of 3 V or less with respect to Li, and in order to exert this effect even at a high temperature, Nb, As, Sb, and Bi are used. Means for incorporating at least one metal selected from the group or a compound of the metal can be said to be effective. In particular, when a composite compound of at least one metal selected from the above group and Li is used, control of the potential and suppression of the catalytic decomposition reaction of the electrolytic solution can be achieved at the same time. Further, as a result of further study, it is preferable that both the sub-active material and the compound of the metal to be added are oxides, and it is preferable that the compound is also a compound oxide when the compound is combined with Li. Was determined.

[0009]

Embodiments of the present invention and comparative examples will be described below with reference to the drawings.

FIG. 1 is a longitudinal section of a coin-shaped battery used to verify the battery characteristics of the embodiment of the present invention and the comparative example.
In FIG. 1, a positive electrode 1 is formed by mixing a carbon powder (5% by weight with respect to the active material) as an active material and an ethylene tetrafluoride resin powder (7% by weight with respect to the active material) as a binder. This is press-formed on a titanium net 3 fixed to the inside of the positive electrode case 2 by spot welding. Also,
The negative electrode 4 is obtained by mixing a powder of a carbonaceous material as an active material with a polyacrylic acid-based resin powder (5% by weight based on the carbonaceous material) as a binder, and spot-welding the inside of the sealing plate 5. It is press-formed on the stainless steel net 6 fixed by the above. These were sealed together with a separator 7 made of polypropylene and an electrolytic solution 8 via a gasket 9 made of polypropylene to obtain a completed battery having a diameter of 20 mm and a height of 1.6 mm. The electrolyte used was one in which 1 mol of lithium perchlorate was dissolved in a mixed solvent of propylene carbonate and ethylene carbonate. This battery is in a discharged state immediately after trial production, and starts from charging.

(Comparative Example 1) A curve shown by a broken line in FIG. 5 indicates a constant current charge / discharge of 2 mA in the case of the battery of Comparative Example 1 (battery using only LiCoO _{2 for the} positive electrode) and a voltage of 4 at the end of charging. 10 shows the charge / discharge voltage characteristics at the 10th cycle when the discharge was performed with the discharge voltage set at 0.1 V and the discharge end voltage set at 3.0 V. In the case of this battery, the average discharge voltage was 3.7V. A curve shown by a broken line in FIG. 6 shows a discharge capacity-cycle characteristic when the charge and discharge are repeatedly performed. As is clear from FIG. 6, even after 100 cycles, the discharge capacity is maintained at 90% or more of the initial value, and the cycle reversibility is excellent. So first, at room temperature (20 ° C)
The degree of deterioration of battery performance due to over-discharge in the battery was examined. Overdischarge is to charge and discharge 10 cycles under the above conditions, take out the battery in a discharged state, discharge it with a resistance of 50 Ω, reach 0 V, and leave it for 10 days with the resistance connected It is. After the 10th cycle of this overdischarge, the battery was charged and discharged again. As a result, the capacity of the charge and discharge voltage characteristics was reduced by nearly 20%. Then, even if the cycle was further repeated, the capacity remained reduced as shown by the solid line in FIG. Therefore,
This battery was found to have deteriorated capacity characteristics by experiencing overdischarge at room temperature.

(Comparative Example 2) Next, the potential of the positive electrode is controlled.
Comparative Example 2 in which over-discharge deterioration is suppressed by adding a sub-active material
The following shows the applied battery. LiCoO in the positive electrode_TwoJoin
LiMn_TwoO _FourUsing an active material containing 5 mol% of
A coin-shaped battery similar to that described above was prototyped. And Comparative Example 1
A charge / discharge test including overdischarge at room temperature was performed under the same conditions as
Was. The curve shown by the broken line in FIG.
In the charge / discharge voltage characteristics of the cell, the characteristics of Comparative Example 1 (breaking of FIG.
Line) and hardly any difference. Also, the discharge volume
The amount-cycle characteristics are also comparative examples as shown by the broken line in FIG.
The characteristics are almost the same as the characteristics of the battery 1 (broken line in FIG. 6).
I understand. Therefore, LiMn is contained in the positive electrode._TwoO_FourAdd
Is at least almost a bad thing for normal charge / discharge characteristics.
It is not considered to have any effect. Then this
After the battery undergoes the same overdischarge as above, charge and discharge again
As a result, as shown by the solid line in FIG.
It was only about 2%. And go further cycles
Even after returning, as shown by the solid line in FIG.
The properties were excellent. As described above, LiMn
_TwoO_FourSuppresses over-discharge deterioration by adding
It became clear that there was an effect. Investigate this cause
As a result of measuring the unipolar behavior of the positive and negative electrodes, it reached 0V
Position where the potential of the positive and negative electrodes at the time is 3.0 V or less with respect to Li
And the deterioration of the capacity characteristics of the negative electrode
It is presumed that was suppressed.

However, the battery was subjected to the same overdischarge in an environment of 60 ° C. and then charged and discharged again. As a result, as shown by the broken line in FIG. 2, the capacity deterioration was about 25%. In particular, as apparent from comparison with FIG. 7, the voltage characteristics particularly changed significantly (polarization increased). Then, even if the cycle was repeated, the characteristics were not recovered and the capacity was kept lowered. In particular, it is expected that the cause of such an increase in polarization is that some side reaction (considered as decomposition of the electrolytic solution) occurs during overdischarge at a high temperature, which inhibits the electrode reaction. . In Comparative Example 2, LiMn ₂ O ₄ was used as a sub-active material. However, other Li-containing composite oxides, for example, those made of Mo, V or Fe and Li, and other than oxides such as Li-containing composite sulfides We also considered the ones. As a result, each showed an effect of controlling the potential although varying to some extent, and was effective in suppressing overdischarge deterioration at room temperature.
However, most of the above-mentioned Li-containing composite compounds have a high temperature (6.
(0 ° C.), the battery deteriorated when overdischarged. Therefore,
It was considered that the means for controlling the potential alone was not enough to suppress overdischarge deterioration at high temperatures.

(Embodiment 1) Next, the potential of the positive electrode is controlled.
Comparative Example 2 in which over-discharge deterioration is suppressed by adding a sub-active material
The battery of the present invention in which the applied battery is further improved
The following shows an example. LiCoO for the positive electrode_TwoPlus LiM
n_TwoO_FourUsed in Comparative Example 2 containing 5 mol% of
And Nb_TwoO_FiveUsing an active material mixed with 3 mol%
Was. Then, a coin-type battery was prototyped with this active material. Next
Then, overdischarge under the same conditions as in Comparative Example 2 at 60 ° C.
After the battery was charged and discharged again,
As indicated by the solid line, the capacity characteristics are the characteristics of the battery of Comparative Example 2.
(Broken line in FIG. 2). further
After that, the cycle was repeated, but the cycle reversibility
Is excellent and has the characteristics and
I got something almost the same. From this result, other
Nb with almost no effect on characteristics_TwoO_FiveBut high temperature
Has the effect of suppressing over-discharge deterioration in
You. In particular, Nb_TwoO _FiveAddition occurs during overdischarge at high temperatures.
Assuming that this side reaction is due to the oxidation catalyst reaction of the positive electrode,
It was performed with the expectation that it would act as a catalyst poison for this reaction.
It was. Thus, Nb_TwoO_FiveBy using
Of the catalyst poison,
By applying it, it is possible to suppress overdischarge deterioration at high temperatures.
It is considered to be. Therefore, there is a possibility as a catalyst poison.
Of Bi, As, Sb, etc. or oxidation of these metals
As a result of examining the effect of adding
Good results were obtained for overdischarge. However, similar effects are expected.
Wait, sulfides such as Nb, Bi, As, Sb and selenide
We examined the addition of a material, but no
Although smaller, the effect is smaller than oxide
Was. In particular, when sulfide or selenide is used, the electrolyte
It is understood that sulfur and selenium components are eluted in the
Was. In addition, it is used as a sub-active material to control the potential of the positive electrode.
In Example 1, LiMn_TwoO_FourWas used but Li_TwoMnO_Four,
Li_ThreeVO_Four, Li_TwoSnO_ThreeAbout other oxides such as
As a result of the investigation, the same effect was exhibited in each case.
I understood. However, it contains Li, which controls the potential of the positive electrode.
If sulfide or selenide is used as a secondary active material,
Excellent effect was obtained with overdischarge at high temperature.
In the same way as described above, sulfur and selenium
Was eluted, and the effect was small. Then, Li
CoO_Two-Active materials and catalysts for controlling the electric potential applied to the catalyst
Further investigation was conducted on both poisoning additives.
As a result, in order to suppress high-
Can be an oxide in any case due to the chemical stability of
It turned out to be desirable.

Next, the amount of a _secondary active material added to LiCoO ₂ for controlling the potential and the amount of an additive acting as a catalyst poison were examined. As a result, the amount of the _secondary active material (composite oxide containing Li) added for controlling the electric potential is at least 3 mol% or more based on LiCoO ₂ , and the amount of the additive (oxide) serving as a catalyst poison is at least 2 mol%. It turned out to be.

(Example 2) Next, the present invention is expected to simultaneously exert the effects of both a sub-active material added to LiCoO ₂ for controlling potential and an additive which becomes a poison for the catalyst. Li ₃ Nb, a composite oxide of Li and Nb
A study was made to add O ₄ . The active material is LiCoO ₂
To which 5 mol% of Li ₃ NbO ₄ was added. Using this active material, a coin-shaped battery similar to that of the above-described example 1 was prototyped. Next, the battery was subjected to overdischarge in a 60 ° C. environment under the same conditions as in Example 1, and then charged and discharged again. FIG. 3 shows the charge / discharge voltage characteristics of this battery, and the characteristics before overdischarge (dashed line in FIG. 3).
And the characteristics (solid line) after experiencing the above-described overdischarge at a high temperature. In the case of this battery as well, the performance deterioration due to the overdischarge at a high temperature is extremely small as in the battery of the present invention of Example 1. It was excellent. After that, the cycle was repeated, but the cycle reversibility was excellent, and the battery characteristics were almost the same as those of the battery that did not undergo overdischarge. Therefore, it is apparent that this battery can simultaneously exert both the potential control and the catalyst poisoning effects without substantially affecting other characteristics.
In the present Example 2, the result regarding the composite oxide of Li and Nb was described. As a result of examining the case where Bi, As or Sb was used instead of Nb, it was found that almost the same effect was obtained.

Next, the amount of the composite oxide added to LiCoO ₂ was examined. As a result, it was found that a sufficient effect can be obtained by adding at least 3 mol% or more to LiCoO _{2 in} any of the above composite oxides. Therefore, the amount of addition is smaller than that of the battery of the present invention described in Example 1, and this means is considered to be a more effective means.

[0018]

As is apparent from the above description, by applying the present invention, even if the battery is over-discharged while being attached to the device, especially if it is over-discharged at a high temperature, it can be recharged. Since the performance is restored, a practically advantageous nonaqueous electrolyte battery can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a coin-type battery used in Examples and Comparative Examples of the present invention.

FIG. 2 is a diagram showing a comparison of charge / discharge voltage characteristics of batteries of Example 1 of the present invention and Comparative Example 2.

FIG. 3 is a diagram showing charge / discharge voltage characteristics of a battery according to Example 2 of the present invention.

FIG. 4 is a diagram showing the unipolar behavior of the positive and negative electrodes during overdischarge.

FIG. 5 is a diagram showing charge / discharge voltage characteristics of the battery of Comparative Example 1.

FIG. 6 is a diagram showing capacity-cycle characteristics of the battery.

FIG. 7 is a diagram showing charge / discharge voltage characteristics of a battery of Comparative Example 2.

FIG. 8 is a diagram showing capacity-cycle characteristics of the battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Positive electrode case 3 Titanium net 4 Negative electrode 5 Sealing plate 6 Stainless steel net 7 Separator 8 Electrolyte 9 Gasket

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/58 H01M 4/02 H01M 4/62 H01M 10/40

Claims (6)

(57) [Claims] 1. A non-aqueous electrolyte secondary battery using a positive electrode using a composite oxide of lithium and cobalt as a positive electrode active material and a negative electrode using a carbonaceous material as a negative electrode material, wherein the positive electrode has N
A composite oxide of at least one metal selected from the group consisting of b, As, Sb, and Bi and lithium is supplied to the secondary battery reaction system.
And the composite oxide of lithium and cobalt is a solid solution
A non-aqueous electrolyte secondary battery that is made to exist as a mixture without becoming a mixture . 2. Nb, As, Sb, Bi mixed in a positive electrode
_2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the lower limit of the composite oxide of at least one metal selected from the group consisting of lithium and lithium is 3 mol% with respect to LiCoO ₂ . 3. A non-aqueous electrolyte secondary battery using a positive electrode containing a mixture of a main active material, a sub-active material, and an additive acting as a catalyst poison, and a negative electrode using a carbonaceous material as a negative electrode material, The main active material is a composite oxide of lithium and cobalt, the sub-active material is a lithium-containing compound having a discharge potential of 3 V or less with respect to Li, and the additive acting as a catalyst poison is Nb, As, A non-aqueous electrolyte secondary battery which is an oxide of at least one metal selected from the group consisting of Sb and Bi. 4. The non-aqueous electrolyte secondary battery according to claim 3, wherein the secondary active material contained in the positive electrode is a lithium-containing oxide. 5. The _secondary active material contained in the positive electrode corresponds to LiCoO ₂ .
The non-aqueous electrolyte secondary battery according to claim 3 , wherein the lower limit is 3 mol% . 6. Additives nonaqueous electrolyte secondary battery to any one of claims 3 to 5 serial <br/> mounting the lower limit 2 mol% relative to LiCoO ₂ positive electrode contains.