JP3558525B2 - How to use non-aqueous secondary batteries - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for using a non-aqueous secondary battery.
[0002]
[Prior art]
2. Description of the Related Art In recent years, cordless devices such as mobile phones and notebook computers have been remarkably popularized, and at the same time, demands for higher capacity and higher energy density of secondary batteries serving as power sources for the devices have been increasing.
[0003]
There is great expectation for non-aqueous secondary batteries such as lithium secondary batteries that have high voltage and high energy density as secondary batteries. Recently, a composite oxide of lithium and a transition metal has been used for the positive electrode, and lithium has been interposed for the negative electrode. Lithium ion secondary batteries using carbonaceous materials capable of calating and deintercalating have been put to practical use.
[0004]
Usually, such a secondary battery is charged to a fully charged state and discharged to a completely discharged state. As a method of charging a non-aqueous secondary battery, generally, a constant current constant voltage charging method is used in which the battery is charged with a constant current until the battery voltage reaches a set value, and then switched to a constant voltage charging. Many proposals have been made, such as JP-A-5-111184, JP-A-6-325794, and JP-A-7-240235. Further, as a method of detecting full charge, Japanese Patent Application Laid-Open Nos. 6-189466, 7-105980, and 7-235332 have been proposed.
[0005]
[Problems to be solved by the invention]
However, the nonaqueous secondary battery full charge - Repeated complete discharge, sufficient cycle life characteristic was a problem that can not be obtained.
[0006]
In view of the above, an object of the present invention is to provide a method of using a non-aqueous secondary battery capable of obtaining excellent cycle life characteristics.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, a method for using a non-aqueous secondary battery of the present invention is a non-aqueous secondary battery including a chargeable / dischargeable positive electrode, an electrolyte, and a chargeable / dischargeable negative electrode, It is characterized in that a region where the state of charge with respect to the rated capacity is equal to or less than a specified value is not used.
[0008]
At this time, detects a closed circuit voltage of the secondary battery during discharge of the nonaqueous secondary battery, the time rate of change of the previous SL voltage is characterized by stopping the discharge if more than 0.2 mV / sec .
[0009]
In addition, the non-aqueous secondary battery is discharged at the first current value, and during the discharge, the battery is discharged at the second current value for a time interval t _1, and the time t ₂ from the start of the discharge at the second current value (where t _{2 2} <and t ₁₎ closed circuit voltage V ₂ of the secondary battery after, that the difference between the closed circuit voltage V ₁ of the following time t ₁ (V ₂ -V ₁₎ is to stop discharging if a specified value or more Features.
[0010]
Wherein the non-aqueous secondary battery are the use, the composite oxide of lithium and transition metal as the positive electrode active material, using a carbonaceous material which lithium can intercalate / de-intercalate as a negative electrode active material in the above And
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
In the lithium ion secondary battery described above, the internal impedance of the battery increases when the state of charge with respect to the rated capacity is extremely low (about 10% or less of the state with respect to the rated capacity). Here, the rated capacity is the capacity when charged by the current charging method.
[0012]
The complex impedance of the secondary battery was measured by a known method, and the results are shown in FIG. In the real component-imaginary component diagram of the impedance shown in FIG. 1, an arc appears in a low frequency region from 10 Hz to 0.1 Hz. However, the above-described arc becomes large in a charged state of 10% or less of the rated capacity. This indicates that the reaction resistance increases in a state of charge of 10% or less of the rated capacity, and when charge and discharge are repeated in such a region where the reaction resistance is large, the reaction between the electrode active material and the electrolytic solution is increased. It is considered that a side reaction other than a normal charging reaction occurs at the interface, which causes deterioration of battery characteristics.
[0013]
Therefore, excellent cycle life characteristics can be obtained by using only the region where the reaction resistance is low without using the region where the reaction resistance is high.
[0014]
In order not to use the region where the reaction resistance is large, the discharge may be stopped before the reaction resistance becomes large during the discharge. As a method for detecting the battery voltage during discharge of the secondary battery, a method of time rate of change of batteries voltage stops discharge if the value of more than 0.2 mV / sec is simple.
[0015]
Further, a discharge with a different current is inserted for a short time during the discharge of the secondary battery, and the battery voltage is measured during the short-time discharge. At this time, the behavior of the battery voltage excluding the voltage change due to the IR drop is affected by the above-described reaction resistance. Therefore, if the reaction resistance is large, the amount of change in the battery voltage is also large. However, since it is difficult to detect the voltage change due to the IR drop itself, there is no problem even if the voltage change due to the discharge in a very short time is used as a substitute for the voltage change due to the IR drop.
[0016]
Accordingly, as shown in FIG. 2, current inserted by the discharge time t ₁ at different current I ₂ and I ₁ during discharge at I _1, the discharge start from the time t ₂ at the current I ₂ ( However, t ₂ <t ₁₎ the difference V ₂ -V ₁ between the battery voltages V ₁ after the battery voltage V ₂ and time t ₁ may be stop discharging if the value of the specified value or more after. At this time, even if a short-time discharge at a current I ₂ different from the current I ₁ is not intentionally inserted, for example, in the case of a personal computer, a large current flows when accessing the hard disk. it is also possible to detect the V ₂ -V _1.
[0017]
As a further method, the method of detecting the amount of charge and discharge of the secondary battery and stopping the discharge before the amount of discharge reaches the amount of charge does not use a region having a large reaction resistance. Can be
[0018]
In addition, since the current lithium ion secondary battery employs a constant current constant voltage charging method, a voltage of about 4.2 V is maintained for a while after entering a constant voltage charging mode. However, when the decomposition voltage of the electrolyte used for the lithium ion secondary battery is 4.2 V or less, a decomposition reaction of the electrolyte occurs during the constant voltage charging, which causes a capacity deterioration accompanying a charge / discharge cycle. Therefore, unless the region where the state of charge with respect to the rated capacity is equal to or more than the specified value is used, more excellent cycle life characteristics can be obtained. Hereinafter, examples of the present invention will be described.
[0019]
【Example】
(Example 1)
First, a cylindrical lithium ion secondary battery was manufactured by the following method.
[0020]
100 parts by weight of LiCoO ₂ powder, which is a positive electrode active material, 3 parts by weight of acetylene black, and 7 parts by weight of a fluororesin binder were mixed to form a positive electrode mixture, which was suspended in an aqueous solution of carboxymethyl cellulose to form a paste. This paste was applied to an aluminum foil, dried and rolled to obtain a positive electrode plate.
[0021]
A mixture of 100 parts by weight of graphite powder, which is a negative electrode active material, and 4 parts by weight of styrene / butadiene rubber was used as a negative electrode mixture, and suspended in an aqueous carboxymethyl cellulose solution to form a paste. This paste was applied to a copper foil, dried and rolled to obtain a negative electrode plate. The positive electrode plate and the negative electrode plate were spirally wound through a separator made of a porous film made of polypropylene, inserted into an A-size container, and sealed. The electrolyte used was a solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and ethyl methyl carbonate.
[0022]
The battery thus prepared was charged at a constant current of 500 mA at 20 ° C., and switched to a constant voltage charge when the battery voltage reached 4.2 V. The charging was completed in a total of 2 hours, and reached a voltage of 3.0 mA at 720 mA. After discharging, it was confirmed that the battery capacity was 780 mAh, and this was defined as the rated capacity.
[0023]
Using the above-mentioned batteries, the cycle life characteristics when using the method of use of the present invention and when using the conventional method of use were compared. As an example using the method of use of the present invention, Sample 1 was discharged at 360 mA and stopped when the rate of change of the battery voltage with respect to time became 0.2 mV / sec or more, which is a specified value . In this case, in order to stop discharging while leaving about 10% of the capacity of the rated capacity, charging was performed at a constant current of 500 mA, and switching to constant voltage charging was performed when the voltage reached 4.2 V, and cutting was performed in 110 minutes in total.
[0024]
Further, the battery was discharged at 270 mA, and a discharge of 650 mA was inserted every 10 minutes for 500 milliseconds (t ₁ ) during the discharge, and the battery voltage 500 milliseconds (t ₁ ) after the start of the discharge at 650 mA and 10 When the difference between the battery voltages after milliseconds (t ₂ ) became 25 mV or more, the discharge was stopped, and Sample 2 was used. In this case as well, in order to stop discharging while leaving about 10% of the capacity of the rated capacity, charging was performed at a constant current of 500 mA, and switching to constant voltage charging was performed when the voltage reached 4.2 V, and cutting was performed in 110 minutes in total. .
[0025]
On the other hand, repetition of the conventional method of full charge-complete discharge, that is, charge is performed at a constant current of 500 mA, and is switched to constant voltage charge when the voltage reaches 4.2 V. Cutting is performed in a total of 2 hours. What repeated the cycle of discharging to 3.0 V at 360 mA was used as a comparative example.
[0026]
The charge and discharge cycles of the examples and comparative examples described above were performed, and the cycle life characteristics obtained as a result are shown in FIG. In Samples 1 and 2 of this example, the capacity of about 10% of the rated capacity was not used, so that the battery capacity at the beginning of the cycle was smaller than that of the comparative example, but the capacity deterioration due to the charge / discharge cycle was small. As the charge and discharge cycle was repeated, the capacity exceeded that of the comparative example.
[0027]
As described above, in the present example, it was found that cycle life characteristics superior to those of the related art were obtained. Similar results were obtained by detecting the charged capacity and the discharged capacity of the battery, and repeating the charge / discharge cycle of stopping the discharge before the discharged capacity reached the charged capacity.
[0028]
(Example 2)
A cylindrical lithium ion secondary battery was manufactured in the same manner as in Example 1, and the battery capacity was 780.
It was confirmed to be mAh, and this was defined as the rated capacity.
[0029]
Using the above-mentioned batteries, the cycle life characteristics when using the method of use of the present invention and when using the conventional method of use were compared. As an example using the method of use of the present invention, the battery is discharged at 360 mA, and when the rate of change of the battery voltage with respect to time becomes 0.2 mV / sec or more, the discharge is stopped to reduce about 10% of the rated capacity. To prevent discharging, charge the battery at a constant current of 500 mA, switch to constant voltage charging when it reaches 4.2 V, cut in 70 minutes in total, and do not charge about 10% of the rated capacity. And
[0030]
On the other hand, repetition of full charge-complete discharge, which is a conventional usage method, that is, charge is performed at a constant current of 500 mA, and is switched to constant voltage charge when the voltage reaches 4.2 V. Cutting is performed in a total of 2 hours. What repeated the cycle of discharging to 3.0 V at 360 mA was used as a comparative example.
[0031]
The charge and discharge cycles of the examples and comparative examples were performed, and the cycle life characteristics obtained as a result are shown in FIG. Since the capacity of about 20% of the rated capacity is not used in the sample 3 of the present embodiment, the battery capacity at the beginning of the cycle is smaller than that of the comparative example, but the capacity deterioration accompanying the charge / discharge cycle is very small. The cycle life characteristics superior to those of the samples 1 and 2 of the example 1 were also exhibited. And the capacity came to exceed the comparative example while repeating the charge / discharge cycle.
[0032]
As described above, in the present example, it was found that a cycle life characteristic which was particularly superior to that of the related art was obtained.
[0033]
【The invention's effect】
As is clear from the above examples, according to the present invention, a method of using a non-aqueous secondary battery having excellent cycle life characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a complex impedance diagram of a lithium ion secondary battery used in the present invention. FIG. 2 is a diagram showing a voltage change when discharging with a different current during discharging of the lithium ion secondary battery used in the present invention. FIG. 3 is a diagram showing cycle life characteristics of a first embodiment and a comparative example of the present invention. FIG. 4 is a diagram showing cycle life characteristics of a second embodiment and a comparative example of the present invention.

Claims (3)

A method for using a non-aqueous secondary battery including a chargeable and dischargeable positive electrode, an electrolyte, and a chargeable and dischargeable negative electrode,
The discharging voltage of the secondary battery is detected during the discharging of the secondary battery, and the discharging is stopped when the rate of change of the closing voltage with time becomes 0.2 mV / sec or more. A method of using a non-aqueous secondary battery, wherein a region in which a charge state with respect to a capacity is equal to or less than a specified value is not used. A method for using a non-aqueous secondary battery including a chargeable and dischargeable positive electrode, an electrolyte, and a chargeable and dischargeable negative electrode,
Discharging the secondary battery at a first current value; _One Only at the second current value and time t from the start of the discharge at the second current value. _Two (However, t _Two <T _One ) The closing voltage V of the secondary battery after _Two And time t _One Closed circuit voltage V _One Difference (V _Two -V _One The method of using a non-aqueous secondary battery according to claim 1, wherein the discharge is stopped when the value of the secondary battery becomes equal to or more than a specified value, so that a region in which the charged state with respect to the rated capacity of the secondary battery is equal to or less than the specified value is not used. The non-aqueous secondary battery uses a composite oxide of lithium and a transition metal as a positive electrode active material, and uses a carbonaceous material capable of intercalating / deintercalating lithium as a negative electrode active material. using the nonaqueous secondary battery of claim 1 or 2 wherein.

Images