JPH11204148A - Discharge capacity recovery method of nonaqueous electrolyte secondary battery and circuit therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an irreversible capacity of a lithium ion secondary battery and improve a discharge capacity by performing discharging of a substantially constant current up to a given voltage at a current value of a specified range. SOLUTION: When discharging is performed, and a voltage of a battery 1 falls down to a given voltage, a discharge stop instruction is outputted from a voltage detector 2 to a switch circuit 5, and a switch circuit 5 cuts the electrical connection between the battery 1 and a terminal 4 in response thereto. Discharging is performed from the battery 1 at a fine current specified by a constant current discharge circuit 3 connected in parallel to the battery 1. Discharge start and end voltages are monitored by the voltage detector 2, and when voltages on both ends of the battery 1 becomes a second given voltage, a discharge capacity recovery stop instructions is outputted, and in response thereto, the switch circuit 5 separates a constant current discharge circuit 3 from the battery 1. Specifically, it is preferable that the battery 1 be overcharged up to 1.0 to 2.0 V at a fine current of 10 mC to 1 mC.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rechargeable non-aqueous electrolyte secondary battery, and more particularly to a method for greatly improving the discharge capacity of a non-aqueous electrolyte secondary battery, and a discharge control circuit therefor. .

[0002]

2. Description of the Related Art In recent years, portable devices such as notebook personal computers, portable telephones, camcorders and the like have been significantly improved in performance, and power consumption has been increasing year by year. For this reason, the required performance of a rechargeable battery as a power source has been increasing at an accelerating rate, for example, it can be used for a longer time. Conventionally, nickel cadmium batteries have been used in the field of such portable devices. However, recently, nickel-metal hydride batteries and lithium batteries have been developed as alternative rechargeable batteries and have begun to be actually used.

[0003] Lithium batteries have 2-3 times the energy density of nickel cadmium batteries. Above all, in a lithium secondary battery using a carbon material for the negative electrode, lithium does not exist in a metallic state in principle, and a charge / discharge reaction always occurs in an ionic state. For this reason, it is called a lithium ion secondary battery,
It has achieved high capacity, high voltage, and high energy density while solving the short circuit problem caused by lithium dendrite growth, which has been a concern in conventional metal lithium secondary batteries.

[0004] However, the lithium ion secondary battery has a capacity loss at the time of the first charge, and has a problem that only 70 to 90% of the packed positive electrode active material can be used. This is due to the irreversibility of the carbon material used for the negative electrode material. That is, the lithium ions once stored in the carbon material are not released.

[0005] It has also been pointed out that if a lithium ion secondary battery is left for a long period of time, such as several months, the capacity is reduced without repeating charging and discharging. This is also due to the irreversibility of the carbon material as in the first charge / discharge.

Various reasons have been considered as causes of the irreversibility of the carbon material, but no conclusion has been reached. For example, it is considered that lithium ions enter pores in the carbon material structure, and the functional groups at the ends of graphene are trapped by lithium ions and are not released again. Alternatively, it is thought that the electrolyte is decomposed on the negative electrode surface to form a surface film (National Techn.
ical Report Vol. 40, No. 4, p. 34, issued on August 18, 1994).

[0007] In a conventional lithium ion secondary battery, a copper foil is used as a current collector of a negative electrode. For this reason,
When overdischarge is performed, there is a problem that the copper foil dissolves and the dissolved copper deposits on the negative electrode during charging, causing an internal short circuit and deterioration of the cell, and overdischarge has been strictly prohibited. For example, in order to prevent this, various measures have been taken such as attaching a protection circuit or attaching a lithium foil to the negative electrode (Japanese Patent Laid-Open No.
5-14472, JP-A-5-14473).

Further, Japanese Patent Application Laid-Open No. 4-331425 discloses an overcharge / overdischarge prevention device when a lithium secondary battery is used.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. That is, conventionally, only the evaluation of the material has been focused on, and the charge / discharge conditions have not been studied in detail.

Accordingly, an object of the present invention is to provide a method for reducing irreversible capacity and improving discharge capacity in a lithium ion secondary battery.

Another object of the present invention is to provide a discharge control circuit for realizing the above method.

[0012]

SUMMARY OF THE INVENTION In order to realize the first aspect of the present invention, a lithium ion secondary battery has a capacity of 10 mC.
From about 1 mC to a predetermined voltage. For example, a lithium-ion secondary battery is 10mC to 1m
By overdischarging to 1.0 to 2.0 V with a small current of C,
It is possible to greatly increase the capacity of the lithium ion secondary battery.

The lithium ion secondary battery has a negative electrode made of a carbon material and a metal foil, and the predetermined voltage is a voltage limited so that the potential of the metal foil is lower than the melting potential of the metal foil. is there. In practice, the predetermined voltage is 1.
It is desirable to be 0V to 2.0V. In the lithium ion secondary battery, when the negative electrode includes a carbon material, the negative electrode may be a graphitized carbon material. In this case, it is desirable that the carbon material has an amorphous structure.

The lithium ion secondary battery has a positive electrode capable of occluding and releasing lithium ions, and the positive electrode is made of a composite oxide of a transition metal and lithium. The composite oxide of the transition metal and lithium is desirably lithium manganate having a spinel structure.

In order to realize another aspect of the present invention, a discharge control circuit is connected in parallel with a lithium ion secondary battery, and is capable of measuring a voltage between both ends of the lithium ion secondary battery; Provided in parallel with the lithium ion secondary battery, a constant current discharge circuit for limiting the discharge current value from the lithium ion secondary battery in the discharge capacity recovery mode, during the discharge mode of the lithium ion secondary battery, One end of the lithium ion secondary battery is controlled to be selectively connected to a discharge terminal according to a voltage detected by the voltage detector, and one end of the lithium ion secondary battery is connected according to an input discharge capacity recovery instruction. It is electrically disconnected from the discharge terminal, and the constant current discharge circuit is connected in parallel with the lithium ion secondary battery and the discharge current value is Comprising a switch circuit for controlling such discharge is performed from the lithium ion secondary battery.

In this case, the discharge control circuit further includes an electric quantity detection circuit that outputs a discharge capacity recovery instruction to the switch circuit when the electric quantity at the time of charging the lithium ion secondary battery becomes equal to or less than a predetermined value. May be. Alternatively, the discharge control circuit may further include an input unit for manually outputting a discharge capacity recovery instruction to the switch circuit.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for recovering the discharge capacity of a nonaqueous electrolyte secondary battery according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of a discharge control circuit that can be used in the method for recovering the discharge capacity of a nonaqueous electrolyte secondary battery according to the present invention.

The discharge control circuit comprises a voltage detector 2, a constant current discharge circuit 3, a switch circuit 5, an electric meter 7, and an input unit 8. The voltage detector 2 and the constant current discharging circuit 3 are provided in parallel with the lithium ion secondary battery 1. The switch circuit includes a discharge terminal 4 and a lithium ion secondary battery 1,
It is connected to a voltage detector 2 and a constant current discharge circuit 3. The electricity meter 7 is connected in series to the lithium ion secondary battery 1, the voltage detector 2, and the constant current discharge circuit 3, and is provided between the discharge terminal 6 and the lithium ion secondary battery 1.

In normal use, the discharge terminal 6, the lithium ion secondary battery 1, and the discharge terminal 4 are connected in series, and the switch circuit 5 has no effect on the normal discharge from the lithium ion secondary battery 1. Has no effect. The voltage detector 2 is connected in parallel to the lithium ion secondary battery 1, and the constant current discharge circuit 3 is not connected to both ends of the lithium ion secondary battery 1. Discharge is performed and the lithium ion secondary battery 1
Is lowered to the first predetermined voltage, a discharge stop instruction is output from the voltage detector 2 to the switch circuit 5. In response to the discharge stop instruction, switch circuit 5 disconnects the electrical connection between lithium ion secondary battery 1 and discharge terminal 4.

Next, when a discharge capacity recovery instruction is input to the switch circuit 5, the switch circuit 5 cuts off the electrical connection between the lithium ion secondary battery 1 and the discharge terminal 4. Further, the constant current discharge circuit 3 is connected in parallel with the lithium ion secondary battery 1. In this case, the voltage detector 2 remains connected to the lithium ion secondary battery 1 in parallel. As a result, discharge from the lithium ion secondary battery 1 is performed with a small current defined by the constant current discharge circuit 3. The voltage detector 2 monitors a discharge start voltage and a discharge start voltage. When the voltage between both ends of the lithium ion secondary battery 1 reaches the second predetermined value, the voltage detector 2 outputs a discharge capacity recovery stop instruction to the switch circuit 5. The switch circuit 5 disconnects the constant current discharge circuit 3 from the lithium secondary battery 1 in response to the discharge capacity recovery stop instruction.

The electricity meter 7 measures the electricity amount of the lithium secondary battery 1 at the time of maximum charge. A display device (not shown) that indicates when the measured amount of electricity falls below a predetermined value.
To inform the user. At the same time, a discharge capacity recovery instruction is output to the switch circuit 5. When reusing the lithium secondary battery 1 after not using it for a while, or after repeatedly performing heavy discharge, the user operates the input unit 8 to send a discharge capacity recovery instruction to the switch circuit 5. Can be output.

Next, the configuration of the lithium secondary battery 1 will be described. FIG. 2 is a configuration diagram of a lithium ion secondary battery used in the present invention. Although this figure shows a cylindrical lithium ion secondary battery, the shape of the battery does not matter in the present invention, and a rectangular battery can be applied.

There are lithium-ion secondary batteries 1 currently in practical use which use lithium cobaltate for the positive electrode and lithium manganate for the positive electrode. The use of metal oxides and polymer materials such as disulfides has been studied. However, the present invention is applicable to any of them.

As the negative electrode of the lithium ion secondary battery 1 currently in practical use, natural graphite, graphitized MCMB,
Although a graphitized carbon material such as graphitized MCF and a non-graphitized carbon material having an amorphous structure are used, the present invention can be applied to any of them as long as the negative electrode is a carbon material.

FIG. 3 is a diagram showing an example of the structure of the lithium ion secondary battery 1. The positive electrode 12 is made of aluminum foil 1
5 and an active material 14 formed thereon. Negative electrode 13
Consists of a copper foil 17 and an active material 16 formed on both surfaces thereof. The positive electrode 12 and the negative electrode 13 face each other with a separator 18 interposed therebetween, and an electrolytic solution 19 is filled between the positive electrode 12 and the negative electrode 13.

Usually, these lithium ion secondary batteries are in a discharged state immediately after production. Once charged at about 0.05-0.3C, left for about one month, and shipped after checking for internal short circuit. In some cases, the product may be shipped after additional steps such as discharging once and charging about half.

Here, 1 C means discharge at a current value such that the capacity of the battery is used up in one hour. In the case of a battery with a capacity of 1000 mAh, 1.0 C discharge means discharge at 1000 mA, and 0.5 C discharge means discharge at 500 mA. In this specification, this charging is referred to as initial charging.

The discharge capacity of the lithium ion secondary battery having undergone such a process is only about 70 to 90% of the initial charge capacity. The charge and discharge after that is about 70 to the initial charge capacity
Done at 90% capacity. That is, of the lithium ions stored in the negative electrode during the first charge, 10
That would be up to 30%. However, the efficiency is almost 100% in the second and subsequent charging and discharging. That is, it can be understood that how much the irreversible capacity at the first time can be reduced is a major factor in determining the battery capacity.

The inventors assumed that this irreversible capacity was due to lithium ions which were taken in the negative electrode but were not released, and thought that the non-released lithium ions could be released by slowly discharging with a weak current. An attempt was made to discharge with a very small current.

Specifically, a lithium ion secondary battery is charged at 10 mC.
It has been found that by overdischarging from 1.0 to 2.0 V with a very small current of 1 mC, the irreversible capacity of the lithium ion secondary battery can be greatly reduced and the battery capacity can be greatly improved. When such overdischarge is performed, for example, when applied to an 18650 type battery, the capacity which was about 1190 mAh in the past has been improved to about 1330 mAh.

Although the details of this cause are not clear,
Lithium ions trapped at the graphene terminals during the first charge and lithium ions that have entered the vacancies inside the carbon structure and have not been released by normal charge / discharge are removed by a very small current, that is, over a long period of time. It is thought that it became possible.

The reason why the initial charge / discharge efficiency does not reach 100% and a slight capacity loss remains is considered to be due to the loss of charge used for forming a film on the negative electrode.

The capacity once recovered did not decrease even after repeated charging and discharging. This is presumably because once lithium ions enter and exit, a conduction path for lithium ions to the internal pores is secured. It has also been found that the discharge rate characteristics of the cell after overdischarge have been improved, which confirms that a movement path for lithium ions has been secured.

This method is also effective for a lithium ion secondary battery whose capacity has been deteriorated by long-term storage.
In general, lithium ion secondary batteries are stored for several months,
The capacity is reduced to 70-90% of the initial value. This is presumably because the negative electrode was kept at a low potential for a long period of time, so that lithium ions penetrated deep into the carbon material that could not be entered by ordinary charging and were not released.

As described above, even in a cell whose capacity has deteriorated due to long-term storage, the capacity can be recovered by overdischarging with a small current. This is also considered to be due to the effect described above.

Further, this method is also effective for a lithium ion secondary battery whose capacity has been reduced after several hundred cycles of charging and discharging. Even after several hundred cycles, the capacity is still degraded. The capacity recovery in this case is slightly less than in the case described above. This is considered to be due to the fact that the capacity deterioration due to the cycle is caused not only by the incorporation of lithium ions but also by other reasons such as deterioration of the electrode material, deterioration of the electrolyte solution, and clogging of the separator. .
In any case, the capacity deterioration due to the lithium ions captured by the negative electrode can be recovered by overdischarging with a minute current.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments. However, the present invention is not limited to the following examples.

First, a lithium ion secondary battery was manufactured by the following method.

The synthesis of the positive electrode active material was performed under the following conditions.
Electrolytic manganese dioxide and lithium carbonate are mixed at a ratio of [Li] / [Mn] = 0.55 when represented by the molar ratio of Li and Mn, and calcined in air at 750 ° C. for 12 hours to produce lithium manganate. Synthesized. X-ray diffraction analysis of the produced lithium manganate confirmed that it had a spinel structure and a single phase.

90.0% by weight of lithium manganate produced by the above method, 5% by weight of graphite powder having an average particle diameter of 6 μm as a conductivity-imparting agent, 2% by weight of acetylene black, and polyvinylidene fluoride (hereinafter referred to as PVDF) as a binder Was weighed at 3 wt%, dispersed in N-methylpyrrolidone (hereinafter NMP) and mixed to form an ink. This ink-like substance was applied on an aluminum foil having a thickness of 20 μm, and dried to remove NMP as a dispersion solvent. The coating was performed on both sides of the aluminum foil, and compression-molded with a roller press so that the thickness including the aluminum foil was 185 μm. Thereafter, it was cut into strips, and a current collecting tab made of aluminum was attached to obtain a positive electrode.

As the negative electrode active material, mesocarbon microbeads (hereinafter referred to as MCMB) manufactured by Osaka Gas and graphitized at 2800 ° C. were used. 88% by weight of MCMB, 2% by weight of acetylene black as a conductivity-imparting agent, and 10% by weight of PVDF as a binder were dispersed and mixed in NMP to form an ink.

This ink-like substance was applied on a copper foil having a thickness of 10 μm and dried to remove NMP as a dispersion solvent. The coating was performed on both sides of the copper foil and compression-molded by a roller press so that the thickness including the copper foil was 175 μm. Then cut into strips, attach the nickel current collection tab,
A negative electrode was used.

The above members were dried at 100 ° C. and 0.1 mmHg or less for 24 hours or more. Then, it was carried into a dry room where the dew point was kept at -40 ° C or lower. Hereinafter, the assembly of the battery was performed in this dry room until the electrolyte was injected and the sealing was completed.
The dried positive electrode and negative electrode are wound through a 25 μm thick polypropylene microporous membrane separator, placed in an 18650 type nickel-plated iron can, impregnated with electrolyte and sealed, 65 mm high, 18 mm diameter cylinder A battery was fabricated.

As a solvent for the electrolytic solution, a mixed solvent of ethylene carbonate as a high dielectric constant solvent and diethyl carbonate as a low viscosity solvent in a volume ratio of 3: 7 was used. The supporting salt is LiPF ₆
Was used at a concentration of 1.0 mol / liter.

Immediately after caulking, charging was performed. Charging is 250m
Ah, constant current charging was performed up to 4.2V, and after reaching 4.2V, switching to constant voltage charging was performed so that the total charging time was 10 hours. This charging is referred to as initial charging in this specification. The capacity at the time of the first charge was 1400 mAh.

The samples described below and the comparative samples were manufactured by the above-described method, and tested using an Mn-based 18650 type lithium ion secondary battery which had been charged for the first time. For the experimental results shown below, at least five samples were prepared for each level, and the average was taken.

The battery was evaluated as follows.

A comparative sample 1 of 18650 cells was prototyped by the above-described method, and was initially charged. Initial charge capacity is 1400mA
h. Subsequently, a constant current discharge was performed at 1.0 A to 3.0 V. This discharge method is a conventional discharge method.

Next, the sample 1 was manufactured by the above-described method,
A constant current discharge was performed at 1.0 A to 3.0 V, and a constant current discharge was performed at 1 mA to 1.0 V. In addition, an 18650 cell was prototyped in the same manner as in Sample 1, and charged for the first time. afterwards,
A discharge test was performed under the following conditions. That is, in Sample 2, a constant current discharge was performed at 1.0 mA at 1000 mA, and in Sample 3, a constant current was discharged at 1.0 mA at 100 mA.
At 0 mA, a constant current was discharged to 1.0 V.
Constant current discharge to 1.0V, Sample 6 discharges constant current to 3.0V at 1mA, Sample 7 discharges constant current to 2.0V at 1mA, Sample 8 discharges constant current to 0.0V at 1mA Was. Thereafter, the discharge capacity was measured, and the charge / discharge efficiency was calculated. Table 1 shows the results.

[0051]

[Table 1]

Next, a cycle life test was performed on Sample 1-8 and Comparative Sample 1. Charge 1.0A
Then, constant current charging was performed up to 4.2V, and when the voltage reached 4.2V, switching to constant voltage charging was performed so that the total charging time was 2.5 hours. Discharge was performed at a constant current of 1.0 A and a cutoff of 3.0 V.
The measurement was performed at 20 degrees. The results for Sample 1 and Comparative Sample 1 are shown in FIG.

As is clear from Table 1, Comparative Sample 1
, The discharge capacity was 1190 mAh and the charge / discharge efficiency was 85%. It is considered that the capacity is low because lithium ions are taken into the negative electrode and not released.

On the other hand, in Sample 1, the discharge capacity was 1330 mA.
h, and the charge / discharge efficiency was 95%. This is considered to be due to the fact that the lithium ions taken into the negative electrode by the minute current were taken out.

As is apparent from FIG. 4, in Sample 1, the initial capacity increase was not reduced, and good cycle characteristics were exhibited. From this, it is considered that under the above conditions, there is no adverse effect on battery performance such as dissolution of copper foil due to overdischarge.

On the other hand, although the comparative sample 1 exhibited good cycle characteristics, the capacity was low even when the cycle was repeated because the initial capacity was lower than that of the sample 1.

As apparent from the above, as the discharge current value was smaller, the discharge capacity was improved. This is considered to be because taking the time as much as possible facilitates the release of the occluded lithium ions deep into the negative electrode carbon material.

However, when the discharge current value became 1 mA or less, the increase in the discharge capacity was saturated. This is considered to be because lithium ions that are not released even at a slow discharge rate of 1 mA or less cannot be released even if the current value is reduced to less than that. On the other hand, if the discharge current value is too low, it takes a long time to discharge, which is not practical.

Further, when the discharge current value was 0.1 mA, deterioration of the cycle characteristics was observed. This is considered to be due to the fact that the time spent for the discharge was extremely long because the discharge rate was low, and the time that the overdischarge state was maintained was very long, so that some side reaction had an adverse effect. Therefore, it is considered that the discharge current value is about 1 mA in the case of 18650 cells, that is, the discharge rate of about 1 mC is the limit. It can be said that the discharge rate at which the effect is remarkably recognized is 10 mA or less for 18650 cells, that is, about 10 mC.

When the discharge current value was fixed at 1 mA, the discharge capacity increased as the discharge cutoff potential was lowered. This is considered to be because lithium ions occluded deeper are easily released by raising the negative electrode carbon material to a higher potential.

However, when the battery was discharged to 0 V, the cycle characteristics deteriorated. This is because the potential of the cell dropped, the negative electrode potential became higher than the dissolution potential of the copper foil used for the current collector, the copper foil dissolved, and eluted during the subsequent cycle test It is considered that copper was reprecipitated on the negative electrode and had an adverse effect on cycle characteristics. From this, it can be said that the effective discharge cutoff potential is 1.0 V to 2.0 V.

Next, the sample 9 and the comparative sample 2, which were manufactured by the method shown in the sample 1 and were subjected to the initial charge and overdischarged, were charged at a constant current of 1.0 A to 4.2 V at a constant current.
When it reaches 2V, switch to constant voltage charging, and the total charging time is 2.5
After charging under the condition of time, it was left for 6 months. The leaving temperature was 20 ° C.

For sample 9, as described above, 1 m
Overdischarge by constant current discharge was performed to 1.0 V at A. Thereafter, the measurement was performed at a constant current of 1.0 A up to 3.0 V, and then the discharge capacity was measured. The left comparative sample 2 was subjected to constant current discharge at 1.0 A to 3.0 V without performing the above constant current discharge, and then the discharge capacity was measured. Table 2 shows the measurement results.

[0064]

[Table 2]

As a result, in Comparative Sample 2, 1150 mAh
Met. This is only 86% of the initial discharge capacity of 1330mAh. This is presumably because the negative electrode was kept at a low potential for a long period of time, so that lithium ions penetrated deep into the carbon material that could not be entered by ordinary charging and were not released.

On the other hand, the capacity of Sample 9 recovered to 1300 mAh. This is equivalent to 98% of the initial discharge capacity of 1330 mAh. As described above, even in a cell having a deteriorated capacity due to long-term storage, the capacity could be recovered by overdischarging with a small current. It is considered that this is because the lithium ions occluded deep into the carbon material came to be released due to overdischarge with a small current.

Thereafter, a charge / discharge test was further performed on Sample 9 and Comparative Sample 2. Sample 9 was subjected to constant current discharge, but the comparative sample 2 was not subjected to constant current discharge. The cycle characteristics were measured in the same manner as in Sample 1. FIG. 5 shows the results.

Sample 9 showed good cycle characteristics. On the other hand, the comparative sample 2 has good cycle characteristics itself, but has a small capacity because the capacity was not recovered first.

Next, manufacturing, initial charging, and overdischarging were performed by the method shown in Sample 1, and overdischarge (constant current discharge) was performed on Sample 10 which had been subjected to a 500 cycle test. The overdischarge condition is 1.0V at 1mA, as in sample 1.
Up to constant current discharge. For comparison, a comparative sample 3 was prepared by performing production, initial charging, and overdischarging by the method shown in Sample 1 and performing a cycle test of 500 cycles. The comparative sample 3 was not subjected to constant current discharge. The discharge capacities of Sample 10 and Comparative Sample 3 were measured. FIG. 6 shows the measurement results.

In sample 10, the capacity after 500 cycles was 1070 mAh, but the capacity was restored to 1160 mAh due to overdischarge. The effect is relatively small as compared with the example immediately after the cell is manufactured or the example of long-term storage.

This is because the capacity deterioration due to the cycle is caused not only because lithium ions are taken in and cannot be released, but also due to other reasons such as deterioration of the electrode material, deterioration of the electrolytic solution, and clogging of the separator. It is thought that there is.

In any case, the capacity deterioration due to the lithium ions captured by the negative electrode can be recovered by overdischarging with a minute current. After that, the cycle test was continued,
It showed good cycle characteristics.

On the other hand, Comparative Sample 3 exhibited good cycle characteristics, but had a small capacity because of no capacity return due to overdischarge.

[0074]

According to the present invention, a lithium ion secondary battery can be used in a range of 10 mC to 1 mC.
By overdischarging to 1.0 to 2.0 V with a very small current of
Lithium ions that have been taken into the negative electrode and have not been released by normal discharge can be released, and the capacity of the lithium ion secondary battery can be greatly increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a control circuit for controlling charging and discharging used in the present invention.

FIG. 2 is a diagram illustrating a configuration of a lithium ion secondary battery.

FIG. 3 is a diagram showing a configuration of a lithium ion secondary battery in detail.

FIG. 4 is a diagram showing the effect of overdischarge on a Mn-based 18650 cell immediately after fabrication.

FIG. 5 is a diagram showing the effect of overdischarge on a Mn-based 18650 cell after being left for 6 months.

FIG. 6 is a diagram showing the effect of overdischarge on Mn-based 18650 cells after 500 cycles.

[Explanation of symbols]

 1: Lithium ion secondary battery 2: Voltage detector 3: Constant current discharge circuit 4, 6: Terminal 7: Electric meter 8: Input unit 12: Positive electrode 13: Negative electrode 14: Positive electrode active material 15: Aluminum foil 16: Negative electrode Active material 17: Copper foil 18: Separator 19: Electrolyte

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[Procedure amendment]

[Submission date] October 28, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

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[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

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[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rechargeable lithium
More particularly, the present invention relates to a method for greatly improving the discharge capacity of a lithium ion secondary battery, and a discharge control circuit therefor.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

The lithium ion secondary battery has a negative electrode made of a carbon material and a metal foil, and the predetermined voltage is a voltage limited so that the potential of the metal foil is lower than the melting potential of the metal foil. is there. In practice, the predetermined voltage is 1.
It is desirable to be 0V to 2.0V. In the lithium ion secondary battery, when the negative electrode includes a carbon material, the negative electrode may be a graphitized carbon material. Further , the carbon material may have an amorphous structure.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

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[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a method for recovering the discharge capacity of a lithium ion secondary battery according to the present invention will be described in detail with reference to the accompanying drawings.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

FIG. 1 is a block diagram showing the configuration of a discharge control circuit that can be used in the method for recovering the discharge capacity of a lithium ion secondary battery according to the present invention. ────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 26, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

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[Claims]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H02J 7/00 302 H02J 7/00 302Z

Claims (10)

[Claims] In a lithium ion secondary battery, 10 mC
A method for recovering the discharge capacity of a non-aqueous electrolyte secondary battery, wherein the battery is discharged at a current of approximately 1 mC to a predetermined voltage at a substantially constant current. 2. The lithium ion secondary battery has a negative electrode made of a carbon material and a metal foil, and the predetermined voltage is a voltage at which the potential of the metal foil is lower than the melting potential of the metal foil. 2. The method for recovering a discharge capacity of a nonaqueous electrolyte secondary battery according to item 1. 3. The method according to claim 2, wherein the predetermined voltage is 1.0 V to 2.0 V. 4. The lithium ion secondary battery has a positive electrode capable of occluding and releasing lithium ions, and the positive electrode is a composite oxide of a transition metal and lithium. The method for recovering a discharge capacity of a nonaqueous electrolyte secondary battery according to any one of the above. 5. The method for recovering a discharge capacity of a nonaqueous electrolyte secondary battery according to claim 4, wherein the composite oxide of a transition metal and lithium is lithium manganate having a spinel structure. 6. The non-aqueous battery according to claim 1, wherein the lithium ion secondary battery has a negative electrode comprising a carbon material, and the negative electrode is a graphitized carbon material. A method for recovering the discharge capacity of an electrolyte secondary battery. 7. The lithium ion secondary battery has a negative electrode including a graphitized carbon material, and the graphitized carbon material has an amorphous structure. Method for recovering discharge capacity of non-aqueous electrolyte secondary battery. 8. A voltage detector connected in parallel with the lithium ion secondary battery and capable of measuring a voltage between both ends of the lithium ion secondary battery, provided in parallel with the lithium ion secondary battery, and recovering discharge capacity. A constant current discharge circuit for limiting a discharge current value from the lithium ion secondary battery in a mode; and, in a discharge mode of the lithium ion secondary battery, the lithium ion secondary battery according to a voltage detected by the voltage detector. One end of the battery is controlled to be selectively connected to the discharge terminal, and one end of the lithium ion secondary battery is electrically disconnected from the discharge terminal in accordance with the input discharge capacity recovery instruction. A circuit is connected in parallel with the lithium ion secondary battery so that the discharge from the lithium ion secondary battery is performed at the discharge current value. Discharge control circuit comprising a switch circuit for Gosuru. 9. The electric quantity detecting circuit according to claim 8, further comprising: an electric quantity detecting circuit for outputting a discharge capacity recovery instruction to the switch circuit when an electric quantity at the time of charging of the lithium ion secondary battery falls below a predetermined value. Discharge control circuit. 10. The discharge control circuit according to claim 8, further comprising an input unit for manually outputting a discharge capacity recovery instruction to said switch circuit.