JPH10134817A - Organic electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery which can suppress the rise of the battery temperature owing to the chemical reaction in overcharging, and can suppress a remarkable breakdown such as bursting or exprosion of the battery. SOLUTION: A positive electrode active material layer 2 is formed by mixing LiCoO2 powder, graphite powder, and PVD (polyvinyliden fluoride), sufficiently at the weight ratio 80:10:10, adding the N-methyl-2-pyridone to be a dispersion solvent in an adequate amount there, and mixing sufficiently, and dispersing them to make into an ink form. Furthermore, a specific amount of lithium nitride is added there, and mixed and dispersed again. The resultant mixture is applied on both surfaces of a positive electrode aggregate 1 by the roll-to-roll transcription, and dried, so as to obtain the positive electrode active material layer 2. By using such positive electrodes, an organic electrolyte secondary battery is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electrolyte secondary battery.

[0002]

2. Description of the Related Art Organic electrolyte secondary batteries typified by lithium secondary batteries are mainly used for portable devices such as VTR cameras, notebook computers and mobile phones, taking advantage of their high energy density. . Particularly in recent years, a so-called lithium ion secondary battery using a material capable of occluding and releasing lithium, such as a carbon material, for a negative electrode has become widespread. The internal structure of this battery is usually wound as described below. That is, the active material is applied to the metal foil for both the positive electrode and the negative electrode. Then, the positive electrode and the negative electrode are wound so as not to be in direct contact with each other with a separator interposed therebetween, housed in a cylindrical can serving as a container, filled with an electrolytic solution, and sealed with a cap. In assembling the battery, the carbon material used as the negative electrode active material is in a state where lithium has been completely released, that is, in a discharged state. Therefore, the positive electrode is usually also in a discharged active material, for example, LiCoO ₂ (lithium cobaltate) or LiNiO ₂ (lithium nickelate).
Are used. The battery can function as a battery by being charged for the first time. Thus, a lithium ion secondary battery that can be charged and discharged as needed is obtained.

[0003]

Generally, an organic electrolyte secondary battery uses a chemically active material as a substance involved in an electrode reaction, and uses an organic electrolyte which deteriorates in performance due to the incorporation of moisture. For such reasons, a sealed structure is provided in which the outside of the battery and the internal components of the battery are completely isolated. Therefore,
If the internal pressure of the battery rises for some reason, the battery may explode and damage peripheral devices. Further, when the battery explodes, there is a possibility that peripheral devices may be damaged. In particular, in the case of a lithium secondary battery, the probability at the time of overcharging becomes extremely high. Normally, a lithium secondary battery is protected by an electric circuit that maintains the current and voltage during charging and discharging properly.However, if this protection circuit fails, the control of the charging upper limit voltage does not work, and the charging As the battery voltage increases, gas is generated by electrolysis of the electrolyte,
Battery internal pressure rises. When this state is further maintained, the battery temperature sharply rises due to Joule heat due to an increase in internal resistance and reaction heat due to a chemical reaction between the electrolyte and the decomposition product of the electrolyte and the active material. The battery in such a state has a high probability of explosion or explosion.

[0004] As a countermeasure against such a problem, a current cut-off mechanism that operates in response to an increase in the internal pressure of the battery is provided in a sealed structure in which the charge current is cut off when the internal pressure of the battery increases due to overcharging. The above amount of electricity is prevented from flowing into the battery. However, even if the charging current is cut off, the temperature rise of the battery cannot be stopped immediately when the above-mentioned chemical reaction is accompanied. Therefore, when the pressure at which the current cutoff mechanism operates is reduced, the battery is operated under normal conditions (protected by a protection circuit) at a warmed ambient environment temperature of 40 to 60 ° C. (frequently in a notebook computer, this temperature is high). The current interruption mechanism operates even when the device is used under the conditions described above. Therefore, there is a restriction that the operating pressure of the current interruption mechanism cannot be set too low. As described above, the lithium secondary battery is dangerously broken such as rupture or explosion due to misuse, erroneous operation, or erroneous operation. Therefore, ensuring the safety of the battery is an extremely important issue.

As a result of a detailed analysis of the situation leading to the explosion of the battery, the present inventors have found that the above-mentioned chemical reaction is involved regardless of the battery temperature at the time of operating the current interrupt mechanism, that is, even if the internal pressure of the battery does not rise so much. Above about 130 ° C,
It was found that the probability of the battery exploding was increased. Several improvements have been made to solve these problems. For example, in JP-A-4-328278 and JP-A-4-329269, the positive electrode contains lithium carbonate or lithium oxalate, and when the battery is overcharged, the lithium carbonate and lithium oxalate are electrochemically decomposed. It has been proposed to generate carbon dioxide gas and to activate the battery internal pressure at an early stage and to activate a current cutoff mechanism that operates in response to the battery internal pressure increase. In particular, JP-A-4-329268 discloses that the molar ratio of lithium to cobalt is Li / C
The positive electrode active material was synthesized under lithium-rich conditions with o greater than 1.0, or the positive electrode active material synthesized with Li / Co = 1.0 and lithium carbonate were mixed and heat-treated to form a positive electrode active material. Contains a lithium layer. However, the positive electrode active material particles synthesized by such a method usually have a large average particle diameter of 10 to 25 μm. When a battery is formed using a positive electrode active material in which particles grow large, there is a demerit that a current density increases due to a small specific surface area of the active material, and high-rate discharge characteristics and low-temperature discharge characteristics deteriorate. Furthermore, simply mixing lithium carbonate into the positive electrode increases the internal pressure of the battery as the battery temperature increases, rather than increasing the internal pressure of the battery due to the generation of carbon dioxide gas due to decomposition of lithium carbonate when the battery is overcharged with a large current. May occur earlier and cause significant destruction. To compensate for these problems, Japanese Patent Application Laid-Open No. 6-33832
No. 3 and JP-A-8-102331, manganese carbonate, cobalt carbonate, nickel carbonate is added to the positive electrode, sodium carbonate, potassium carbonate, rubidium carbonate,
It contains magnesium carbonate, calcium carbonate and barium carbonate. Nevertheless, when the inventor of the present invention conducted a tracing experiment, the effect was not always sufficient. As a result of vigorous and detailed examination of such a situation, it was found that the cause was the average particle diameter of the carbonate. In each of the above publications,
Although it is described that carbonate is electrochemically decomposed and generates carbon dioxide gas, according to a detailed analysis of the present inventors, not only the carbonate is decomposed, but also the interaction with an organic electrolyte. It was found that decomposition and gas generation occurred together with the organic electrolyte. Moreover, it was found that the generated gas was not oxygen gas but mainly oxygen-based gas. Therefore, when the average particle diameter of the carbonate is large,
Since the surface area is small, the decomposition reaction accompanied by the interaction with the electrolytic solution is not sufficiently promoted, and it is difficult to sufficiently increase the internal pressure of the battery and operate the current cutoff mechanism at a desired timing.

[0006] Further, the carbonate is electrochemically decomposed at a potential lower than the decomposition voltage of the organic electrolyte, but when the battery is overcharged with a large current, the battery voltage rapidly increases. Because of the rise, the decomposition voltage of the carbonate exceeded the decomposition voltage of the above-mentioned carbonate, and easily reached the decomposition voltage of the organic electrolyte. In addition, even if the above-mentioned carbonates of various metals are contained in the positive electrode, decomposition of the electrolytic solution cannot be suppressed at the time of overcharging, and a rise in battery temperature due to the decomposition cannot be suppressed. The problem to be solved by the present invention is
The purpose of the present invention is to suppress a rise in battery temperature due to a chemical reaction at the time of overcharging as described above, and to suppress remarkable destruction such as bursting or explosion of a battery.

[0007]

According to the present invention, there is provided a valve according to the present invention, wherein a positive electrode, a negative electrode and an organic electrolyte are housed in a closed container, and the closed container is opened at an internal pressure higher than a predetermined pressure. Organic electrolyte secondary battery having a mechanism,
The positive electrode contains lithium nitrate (LiNO ₃ ). As a result, the current cutoff mechanism can be quickly operated, and the above-described abnormal reaction and the increase in battery temperature caused by the abnormal reaction can be reliably suppressed.

[0008] In the above structure, it is preferable that a current cut-off mechanism that operates when the internal pressure of the battery rises is provided, and the current cut-off mechanism operates at a lower battery internal pressure than the internal pressure of the battery at which the valve mechanism opens. The reason is that even if the overcharge becomes excessive and the electrochemical decomposition of the organic electrolyte and / or lithium nitrate is promoted, the organic electrolyte secondary battery has a current cut-off mechanism that operates by increasing the internal pressure of the battery. The current cutoff mechanism has a configuration in which the valve mechanism operates at a battery internal pressure lower than the battery internal pressure at which the valve mechanism is opened, whereby the charging current can be quickly interrupted against an excessive increase in battery internal pressure,
Battery safety is improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a cylindrical lithium secondary battery embodying the present invention. Reference numeral 1 denotes a positive electrode current collector, which is an aluminum foil having a thickness of 20 μm. The plane size is 50 mm × 450 mm. Reference numeral 2 denotes a positive electrode active material layer, in which lithium ions are used as an electrode reactive species, lithium can be released and occluded, a positive electrode active material LiCoO ₂ , graphite as a conductive additive, polyvinylidene fluoride (PVDF) as a binder, and an electrolytic solution. It is composed of A detailed manufacturing method of the positive electrode active material layer 2 will be described. 80: 10: 1 by weight ratio of LiCoO ₂ (average particle size: about 1 to ₂ μm) powder, graphite (average particle size: about 0.5 μm) powder, and PVDF
0, and mixed with N-methyl-2 as a dispersion solvent.
Add an appropriate amount of pyrrolidone, knead and disperse sufficiently to form an ink. Further, a predetermined amount of lithium nitrate is added there,
Knead and disperse again. The kneaded material is applied to both surfaces of the positive electrode current collector 1 by roll-to-roll transfer and dried to obtain the positive electrode active material layer 2. (However, no electrolyte is contained at this stage.) The thickness of the positive electrode active material layer 2 is 100 μm on each side of the positive electrode current collector 1. 3 is a negative electrode current collector having a thickness of 10 μm.
m copper foil. The plane size is 50 mm × 490 mm. Reference numeral 4 denotes a negative electrode active material layer, which comprises lithium ion as an electrode reactive species, amorphous carbon as a negative electrode active material capable of releasing and occluding lithium, polyvinylidene fluoride (PVDF) as a binder, and an electrolytic solution. Be composed.
A detailed method for forming the negative electrode active material layer 4 will be described. Amorphous carbon and PVDF are mixed in a weight ratio of 90:10, and an appropriate amount of N-methyl-2-pyrrolidone as a dispersion solvent is added thereto, and the mixture is sufficiently kneaded and dispersed to form an ink. The kneaded material is applied on both sides of the negative electrode current collector 3 by roll-to-roll transfer and dried to obtain the negative electrode active material layer 4. (However, no electrolyte is contained at this stage.) The thickness of the negative electrode active material layer 2 is 100 μm on both sides of the negative electrode current collector 3. Reference numeral 5 denotes a separator, which is a microporous polyethylene film having a thickness of 25 μm. It is wound so that the separator 5 is arranged between the positive electrode and the negative electrode, and inserted into the negative electrode can 6. Then, the tab terminal which has been welded to the negative electrode current collector in advance is welded to the negative electrode can 6. 7 is a positive electrode cap and 8 is a positive electrode tab terminal. The positive electrode tab terminal 8 is welded to the positive electrode current collector 1 in advance, and then welded to the positive electrode cap 7. Next, 5 ml of the electrolytic solution was added to the negative electrode can 6.
Inject into. The electrolyte was a mixed solvent of propylene carbonate, dimethyl carbonate and diethyl carbonate in which 1 mol / l of LiPF ₆ was dissolved, and the mixing ratio was 30: 5 by volume.
5:15. 9 is an insulating gasket. The positive electrode cap 7 is arranged on the upper part of the negative electrode can, and the upper part of the negative electrode can is caulked via the gasket 9 to seal the battery. Here, in the positive electrode cap 7, a current cutoff mechanism (pressure switch) that is activated by an increase in the battery internal pressure and a valve mechanism that is opened by a battery internal pressure higher than the battery internal pressure at which the current cutoff mechanism is activated are incorporated. . The pressure switch is, specifically, a positive current collecting terminal and a positive external terminal (from the appearance of the battery,
(A member expressed as a positive electrode terminal). In addition, the valve mechanism used was a non-return type, that is, a valve mechanism which does not return to the original state (a state in which the battery is sealed) once the internal pressure of the battery becomes excessively high and the valve operates. However, a return type valve mechanism may be adopted. As the above-mentioned "current interruption mechanism operated by battery internal pressure", a mechanism which operates at a battery internal pressure of 6 to 8 kg / cm ² was used. In addition, the valve of the "valve mechanism current interrupt device is opened actuated by high battery internal pressure than the internal pressure of the battery to operate", it was used as the battery internal pressure is opened at 10-15 kg / cm ^2. These values can be set arbitrarily. What is necessary is just to design according to the intended use of a battery. For example, when it comes to valves,
The design can be easily changed by adjusting the material, thickness, area and the like of the valve.

[0010] By including lithium nitrate in the positive electrode,
If the battery voltage rises during overcharge, gas generation and battery internal pressure rise can be promptly promoted, and the current cutoff mechanism can be activated at an early stage to suppress battery temperature rise. This effect is hardly dependent on the particle size of lithium nitrate.

[0011]

EXAMPLES Batteries (Examples) manufactured according to the description of the embodiment of the invention and batteries of Conventional Examples 1 to 12 described below were manufactured and compared. In Conventional Example 1, the lithium ion was not added to the positive electrode. Conventional example 2 is lithium carbonate for the positive electrode, conventional example 3 is lithium oxalate, conventional example 4 is manganese carbonate, conventional example 5 is cobalt carbonate, conventional example 6 is nickel carbonate, and conventional example 7
Is sodium carbonate, Conventional Example 8 is potassium carbonate, Conventional Example 9
Is a rubidium carbonate, Conventional Example 10 is calcium carbonate, Conventional Example 11 is magnesium carbonate, and Conventional Example 12 is barium carbonate.

In the batteries of Examples and each of the conventional examples, the addition amount of lithium nitrate and other various carbonates and oxalates is 0.05 to 20% based on the weight of the positive electrode active material LiCoO _2.
And The average particle size of various carbonates and oxalates is 1 μm.
４０40 μm. The produced battery was charged under the following conditions. After discharging, the battery was continuously charged at 2.8 A, and was placed in an overcharged state. Tables 1 and 2 show the battery destruction at that time.
Shown in In the numerical values in the table, the upper row shows the battery discharge capacity (mA).
h), the lower row shows the rate of rupture or explosion when the battery is overcharged (%). The substances described in parentheses in the table are the names of additives contained in the positive electrode. The overcharge test was performed at an ambient temperature of 25 ° C., and the average particle size of lithium nitrate and various carbonates was 5 μm. Charge: 4.2V constant voltage, upper limit current 100mA, 20h,
Ambient temperature 25 ° C Discharge: 100mA constant current, final voltage 2.8V, ambient temperature 25 ° C

[0013]

[Table 1]

[0014]

[Table 2]

As is clear from Tables 1 and 2, by adding lithium nitrate to the positive electrode, remarkable destruction of the battery, such as rupture or explosion when falling into overcharge, is suppressed.
Lithium nitrate is 0.2% by weight based on the weight of the positive electrode active material
Above, a more remarkable effect can be obtained. On the other hand, when the addition amount of lithium nitrate exceeds 15% by weight, the discharge capacity sharply decreases. The reason is considered to be that the internal resistance of the battery was increased due to the low electronic conductivity of the additive.

Table 3 shows that the average particle size of lithium nitrate in the above overcharge test was 5, 10, 15, 20, 25,
The figure shows the rate (%) of bursting and explosion of the battery when the added amount is 5%, and the battery is 30, 35, and 40 μm.

[0017]

[Table 3]

When the average particle size is 30 μm or less, the rate of burst and explosion is 0%, which is preferable.
The reason why the effect is somewhat reduced when the average particle size exceeds 30 μm is considered to be because the surface area of lithium nitrate is reduced, the sensitivity to the increase in battery voltage is reduced, and the gas generation rate is reduced.

In the battery of Conventional Example 1, the probability is very high.
Although the battery exploded and exploded, the probability is reduced in Conventional Examples 2 to 12. However, the effect is inferior to that of the battery of the example to which lithium nitrate was added. In order to investigate the reason, a part of both the positive electrode and the negative electrode of each battery in a fully charged state was taken out, and the positive electrode was used as a working electrode and the negative electrode was used as a counter electrode to scan toward a high voltage side. Scanning speed is 0.1mV
/ Sec, test temperature 30 ° C. Conditions are as follows.
The size of the electrode cut out for the test is 2
0 mm × 20 mm, and the negative electrode is 21 mm × 21 mm.
The cut positive electrode and negative electrode were a bipolar cell in which a separator was opposed to each other, and voltage scanning was performed in the same electrolytic solution. Here, the reference electrode is not used. This is because the potential of the counter electrode (negative electrode) during voltage scanning hardly changes. Therefore, even if metal lithium or a lithium alloy is used for the negative electrode, or a negative electrode material capable of occluding and releasing lithium other than amorphous carbon, for example, a highly crystalline carbon material such as graphite, is also shown in FIG. It is thought that the same result as the result is obtained.

The results of the voltage scanning are shown in FIGS. FIG.
FIG. 3 shows the result of voltage scanning using the electrode of the battery of the example in which lithium nitrate was added to the positive electrode. FIG. 3 shows the result of voltage scanning using the electrode of the battery of Conventional Example 1 in which nothing was added to the positive electrode.
FIG. 4 shows the result of voltage scanning using the electrode of the battery of Conventional Example 2 in which lithium carbonate was added to the positive electrode, and FIG. 5 shows the result of voltage scanning using the electrode of the battery of Conventional Example 3 in which lithium oxalate was added to the positive electrode. FIG. 6 shows the result of voltage scanning using the electrode of the battery of Conventional Example 4 in which manganese carbonate was added to the positive electrode. FIG. 7 shows the result of voltage scanning using the electrode of the battery of Conventional Example 8 in which potassium carbonate was added to the positive electrode. FIG. 8 shows the results of voltage scanning using the electrode of the battery of Conventional Example 11 in which magnesium carbonate was added to the positive electrode. The current peak observed near 4.6 V in FIGS. 2 to 8 is not the peak due to the electrochemical decomposition of the electrolyte or the additive, but the oxidation peak of the positive electrode. In FIG. 3, as a result of voltage scanning using the electrode of the battery of Conventional Example 1 in which nothing is added to the positive electrode, an increase in the current value corresponding to decomposition of the electrolyte from about 5.1 V is observed. This is in agreement with the test result that when the battery is overcharged and the voltage becomes about 5.1 V or more, the probability of the battery exploding or exploding becomes considerably high. The result of voltage scanning using the electrode of the battery of Conventional Example 2 in which lithium carbonate was added to the positive electrode in FIG. 4 shows that the lithium carbonate and the electrolyte were at about 5 V lower than the voltage at which the current corresponding to the decomposition of the electrolyte flows. A current peak corresponding to the decomposition reaction of
This is consistent with the description in JP-A-78. However, 5.5
From around V, a sharp increase in the current value due to the decomposition of the electrolytic solution was observed. As shown in FIGS. 5 to 8, Conventional Examples 3 and 4, in which various carbonates and lithium oxalate were added,
The results of voltage scanning using the electrodes of the batteries of Conventional Example 8 and Conventional Example 11 show that at a voltage lower than the voltage at which the current corresponding to the decomposition of the electrolytic solution flows, the current corresponding to the decomposition reaction between the additive and the electrolytic solution is obtained. Is not observed. Therefore, it can be said that the additive has almost no effect.

According to the results of voltage scanning using the electrodes of the batteries of Conventional Examples 1 to 4, 8, and 11 (FIGS. 3 to 8), when the voltage exceeds 5.1 V, the current value corresponding to the decomposition reaction of the electrolytic solution is obtained. Is observed. Therefore, FIGS. 3 to 8 suggest that when the battery suddenly falls into an overcharged state with a relatively large current, bursting and explosion cannot be suppressed. On the other hand, in the result of voltage scanning using the electrode of the battery of the present invention in which lithium nitrate was added to the positive electrode in FIG. 2, when the voltage exceeded 5.1 V, an increase in the current value corresponding to the decomposition reaction of the electrolyte was observed. However, a current peak which is considered to correspond to the decomposition reaction between lithium nitrate and the electrolyte is observed at around 4.7 V and 4.8 V before that. Gas generation was visually confirmed from around 4.7V. Therefore, in a battery in which lithium nitrate is added to the positive electrode, decomposition gas generation of the additive occurs at a voltage lower than a voltage at which a current corresponding to decomposition of the electrolyte flows,
It can be seen that the internal pressure of the battery rises before a dangerous state occurs, and the current cutoff mechanism or the valve mechanism is operated, so that rupture and explosion can be avoided.

In this embodiment, LiCoO ₂ is used as the positive electrode active material, but other positive electrode active materials, for example, LiNiO ₂ ,
Even if LiMnO ₂ or the like is used, the same effect as that of the present embodiment can be obtained.

[0023]

According to the present invention, the internal pressure of the battery can be rapidly increased even in the case of a sudden increase in the battery voltage in the overcharge region. As a result, the operation of the current interrupting mechanism due to the increase in the internal pressure of the battery is ensured. The current interrupt mechanism is activated before an abnormal reaction occurs, in which the electrolyte is rapidly decomposed.The secondary solution of the organic electrolyte, which can prevent the battery temperature from rising and suppress remarkable destruction such as rupture or explosion of the battery, can be achieved. Battery could be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an example of an organic electrolyte secondary battery of the present invention.

FIG. 2 shows the results of voltage scanning using the electrodes of the battery of the example in which lithium nitrate was added to the positive electrode.

FIG. 3 shows the result of voltage scanning using the electrode of the battery of Conventional Example 1 in which nothing is added to the positive electrode.

FIG. 4 shows the result of voltage scanning using the electrode of the battery of Conventional Example 2 in which lithium carbonate was added to the positive electrode.

FIG. 5 shows the result of voltage scanning using the electrode of the battery of Conventional Example 3 in which lithium oxalate was added to the positive electrode.

FIG. 6 shows the result of voltage scanning using the electrode of the battery of Conventional Example 4 in which manganese carbonate was added to the positive electrode.

FIG. 7 shows the result of voltage scanning using the electrode of the battery of Conventional Example 8 in which potassium carbonate was added to the positive electrode.

FIG. 8 shows a conventional example 11 in which magnesium carbonate is added to a positive electrode.
3 shows the results of voltage scanning using the electrodes of the battery of FIG.

[Explanation of symbols]

 1. 1. positive electrode current collector 2. positive electrode active material layer Negative electrode current collector 4. Negative electrode active material layer 5. Separator 6. Negative electrode can 7 Positive electrode cap 8. Positive electrode tab terminal 9. gasket

Claims (6)

[Claims] An organic electrolyte secondary battery comprising a positive electrode, a negative electrode, and an organic electrolyte housed in a closed container, wherein the closed container has a valve mechanism that is opened at a battery internal pressure higher than a predetermined pressure. An organic electrolyte secondary battery, wherein the positive electrode contains lithium nitrate. 2. The organic electrolysis according to claim 1, further comprising a current cutoff mechanism that operates when the internal pressure of the battery rises, wherein the current cutoff mechanism operates at a lower battery internal pressure than when the valve mechanism opens. Liquid secondary battery. 3. The organic electrolyte secondary battery according to claim 1, wherein the content of lithium nitrate is 0.2 to 15% based on the weight of the positive electrode active material. 4. The organic electrolyte secondary battery according to claim 1, wherein the average particle diameter of lithium nitrate is 30 μm or less. 5. The positive electrode is a material capable of releasing and occluding lithium during charging and discharging, and the negative electrode is selected from lithium metal, lithium alloy, and a material capable of occluding and releasing lithium. Item 6. The organic electrolyte secondary battery according to any one of Items 1 to 4. 6. The positive electrode is a material capable of releasing and occluding lithium during charge and discharge, and the negative electrode is a carbon material capable of occluding and releasing lithium.
5. The organic electrolyte secondary battery according to any one of 4.