JP3186811B2 - Method of charging lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention is an internal At a charging of the lithium secondary battery, a pulse current in a charging method of loading alternately to the charging direction and the discharging direction, even if repeated charging and discharging in particular a number of times The present invention relates to a safe charging method for a lithium secondary battery without danger of short circuit.

[0002]

2. Description of the Related Art In order to respond to market needs for smaller, lighter and higher performance electric and electronic devices, which have been increasing in recent years,
The development of a secondary battery having a higher energy density than the conventional frame is expected. Secondary batteries using metallic lithium as a negative electrode active material have the advantages of a wide operating temperature range and good storage characteristics in addition to the excellent characteristics of high voltage and high energy density. It is drawing attention as a next-generation battery that replaces the next battery.

[0003]

However, in a secondary battery using metallic lithium as a negative electrode active material, when charge and discharge are repeated many times, dendrites grow from the surface of the negative electrode lithium, causing a short circuit between the internal electrodes. There are many technical issues in using in general market, such as the risk of ignition and the generation of electron conductive isolated metallic lithium, which deteriorates the charging and discharging efficiency. . Batteries using lithium alloy as a negative electrode active material to deal with this problem, and the like battery using interlayer intrusion of lithium (intercalation reaction) by using a carbon material is examined in the negative electrode, any This also impairs the high energy density characteristics possessed by the lithium secondary battery.

[0004] It is an object of the present invention to solve the above-mentioned problems and to provide a lithium secondary battery which has no risk of ignition due to a short circuit between electrodes during use and has excellent charge / discharge cycle characteristics. .

[0005]

Means for Solving the Problems The present invention has been made to achieve the above object, and is characterized in that when charging a lithium secondary battery, a pulse current is alternately loaded in a charging direction and a discharging direction to perform charging. . That is, while the conventional charging method uses a continuous DC current, the present invention applies a pulse current having a frequency of 0.1 Hz to 10 KHz as shown in FIG. 1 and a current value of 1 μA / cm ^{2 in the} charging direction. Or 100m
A / cm ² , one-fourth of the current value in the charging direction in the discharging direction
The charge and discharge are alternately and continuously repeated alternately at the following current values (not including 0), and the generation of dendrite on the surface of the negative electrode is suppressed by forcibly flowing the anode current, and the deposition of metallic lithium on the surface of the negative electrode To provide a lithium secondary battery having a long life and excellent safety.

That is, the present invention provides: A charging method for a lithium secondary battery, characterized in that when charging a lithium secondary battery, a pulse current is alternately loaded in a charging direction and a discharging direction of the battery to perform charging. 2. 2. The method for charging a lithium secondary battery according to claim 1, wherein the current value in the charging direction is 1 μA / cm.
^A method for charging a lithium secondary battery, wherein the current value in the discharging direction is ² to 100 mA / cm ² and the current value in the discharging direction is a quarter or less (not including 0) corresponding to the current value in the charging direction. It is. 3. 2. The method according to claim 1, wherein the frequency of the pulse current of the charging current is 0.5.
A method for charging a lithium secondary battery, wherein the frequency is 1 Hz to 10 KHz.

[0007]

In the method of charging a lithium secondary battery according to the present invention, the maximum value of the charging pulse current in the charging direction is 10
It is 0 mA / cm ² , and by using a pulse current, it is possible to charge the battery with a larger current than the usual method of charging a lithium secondary battery. However, 100 mA /
If it exceeds cm ² , the electrolytic solution will be decomposed, or the form of lithium deposition on the negative electrode will be non-uniform, and the charge / discharge characteristics will deteriorate. On the other hand, the effect of the present invention is exerted by setting the current value in the discharging direction to 1/4 or less of the current value in the charging direction.

The frequency of the pulse current is in the range of 0.1 Hz to 10 KHz. However, in the frequency range of less than 0.1 Hz, the effect of the pulse current is reduced, and the cycle efficiency is deteriorated in practical use as in the case of the DC current. Is seen. On the other hand, in the frequency cycle exceeding 10 KHz during charging, the cycle efficiency of the charge / discharge characteristics is deteriorated as described above. By applying the above-described charging method to a lithium secondary battery, a lithium secondary battery having excellent charge / discharge cycle characteristics can be obtained.

[0009]

An embodiment of the present invention will be described. A battery was constructed using metal lithium as a negative electrode active material, manganese dioxide as a positive electrode active material, and a solution of lithium perchlorate (LiClO ₄ ) having a concentration of 1N dissolved in propylene carbonate (PC) as an electrolyte. . The battery performs cycle test of charge and discharge under the conditions shown in Table 1 were used to evaluate the charge-discharge characteristics by measuring the discharge capacity during discharge cycle degree. FIG. 2 shows the relationship between the number of charge / discharge cycles and the decrease rate of the discharge capacity (the initial discharge capacity is 100%) when a charge / discharge cycle test is performed using a pulse current having a frequency of 100 Hz during charging. ,
The discharge characteristics for each charging current value are shown corresponding to the numbers of the respective examples shown in Table 1. In addition, 0.1 as a comparative example
FIG. 2 shows charge / discharge cycle characteristics when charge / discharge was performed using a constant current of mA / cm ² . As is clear from the characteristic diagram of FIG. 2, in the charging method of the present invention, by using the pulse charging method in which the charging current and the discharging current are asymmetric, the capacity of the lithium electrode is reduced as compared with the case of continuous DC current. And the charge / discharge cycle life is remarkably improved.

[Table 1]

In Table 1, the minus sign on the discharge side indicates the direction of discharge. FIG.
Shows the relationship between the number of charge / discharge cycles and the rate of decrease in discharge capacity for an example in which a charge / discharge cycle test was performed under the same pulse current value and different frequency during charging. In addition, the comparative example at the time of performing charge by continuous direct current and discharging is also shown in the same figure. As is clear from the characteristic diagram of FIG. 3, the charge / discharge cycle life is significantly improved by using the charging method according to the present invention as compared with the case of charging by continuous DC current.

[0011]

As described above, in the charging method according to the present invention, the respective current values alternately change between the charging direction and the discharging direction in the charging direction, where the current value is 1 μA / cm ² to 100 mA / 100 mA / cm ^2.
cm ² , the discharge direction is not more than one-fourth (excluding 0) of each charging current, and the frequency is 0.1 Hz to 1
By charging a lithium secondary battery by applying a pulse current of 0 KHz, the life of the charge / discharge cycle is superior to that of the conventional charging method using continuous DC current, and the generation of dendrites between the electrodes is reduced. In addition, it is possible to provide a method for charging a lithium secondary battery in which the danger of an internal short circuit is eliminated and safety is dramatically improved. In the embodiment of the present invention, the pulse alternating current shown in FIG. 1 is used. However, the same effect as that of the present invention can be obtained in a sine wave current and an alternating current accompanied by a slight transient phenomenon. That is clear.

[Brief description of the drawings]

FIG. 1 is a diagram showing a waveform of a pulse current that is a charging current during charging.

FIG. 2 is a characteristic diagram showing charge-discharge conditions indicating the numbers of the examples shown in Table 1 and cycle characteristics of the discharge capacity reduction rate .

FIG. 3 is a characteristic diagram showing the charge-discharge conditions indicated by the numbers of the examples shown in Table 1 and the cycle characteristics of the discharge capacity reduction rate .

Continuation of the front page (56) References JP-A-3-274682 (JP, A) JP-A-62-282672 (JP, A) JP-B-46-31702 (JP, B1) (58) Fields investigated (Int) .Cl. ⁷ , DB name) H01M 10/42-10/48 H02J ⁷ /00-7/36

Claims (3)

(57) [Claims] 1. A method for charging a lithium secondary battery, comprising: charging a lithium secondary battery by applying a pulse current alternately in a charging direction and a discharging direction of the battery. 2. The method for charging a lithium secondary battery according to claim 1, wherein a current value in a charging direction is 1 μA / cm ² to 100 mA / cm ² , and a current value in a discharging direction is a current value in a charging direction. A value of not more than a quarter (not including 0) corresponding to the following. 3. The method for charging a lithium secondary battery according to claim 1, wherein the frequency of the pulse current of the charging current is 0.1H.
Lithium 2 having a frequency of z to 10 KHz
How to charge the next battery.