JP2006286562A - Charging method of secondary cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optimal charging method for each secondary cell. <P>SOLUTION: The charging method of a secondary cell moves to constant-potential charge after constant-current charge. The charging method of a secondary cell is such that constant-potential charge is once processed with first predetermined voltage at the time of achieving to the first predetermined voltage by the constant-current charge, time duration damping rate of the current is calculated of the time. Then a propriety of constant-current charge to second predetermined voltage is determined based on the damping rate. When the determination is possible to charge, the constant-current charge is processed to the second predetermined voltage, then the constant-voltage charge is processed with the second predetermined voltage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for charging a secondary battery.

  Secondary batteries such as nickel-hydrogen secondary batteries and lithium ion secondary batteries are widely used as power sources for portable devices as power sources that can be repeatedly charged and discharged. As a method for charging the secondary battery, a method in which constant current charging and constant voltage charging are combined is known.

  In this constant current charging + constant voltage charging method, charging to a set voltage is first performed with a constant current, and then constant voltage charging is performed.

There are various reports about the improvement (for example, Patent Document 1).
JP-A-9-107638

  For example, in the case of a lithium ion secondary battery, there are several materials such as LiCoO 2 and LiNiO 2 as the positive electrode active material, but the charging behavior of the battery differs depending on the difference in the materials used and the deterioration state of the battery.

  Therefore, the set voltage of the constant current charging + constant voltage charging method may not necessarily be the optimum value for the battery. If the set voltage is lower than the optimum value, charging at an initial constant current is not sufficient, and there is a problem that charging is insufficient even if charging is performed for a predetermined time.

  On the other hand, when the set voltage is increased, some batteries are overcharged, and there is a problem that the deterioration of the battery is promoted.

  In order to solve the above-described problem, the present invention provides a charging method for a secondary battery that shifts to constant voltage charging after constant current charging, and once the first set voltage is reached by constant current charging, Constant voltage charging is performed at the first set voltage, the time decay rate of the current at that time is obtained, and whether or not constant current charge up to the second set voltage is possible is determined based on the decay rate. The secondary battery charging method is characterized in that constant-current charging is performed up to a set voltage, and then constant-voltage charging is performed at a second set voltage.

  By using the charging method of the present invention, it is possible to optimally charge individual secondary batteries.

  According to the present invention, it is possible to optimally charge individual secondary batteries.

  Normally, when charging a secondary battery with constant current charge + constant voltage charge method, if the battery is charged to a deep charge state during constant current charge, the charge acceptability of the secondary battery at the time of shifting to constant voltage charge Decreases and the time decay rate of current in constant voltage charging increases.

  On the other hand, when only a shallow charge state is charged during constant current charging, the secondary battery has high charge acceptability at the time of shifting to constant voltage charging, so the time decay rate of current in constant voltage charging is small. . In that case, even if charging at a constant current is continued, the battery is not damaged and can be charged efficiently.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a flowchart of the charging method of the present invention. I will explain in order.

  Charging is started, and first constant current charging in the first cycle is performed. Thereafter, the constant current charging is terminated when the first set voltage is reached. Next, constant voltage charging is performed with the first set voltage. At this time, the time decay rate of the current is obtained. When the current decay rate is equal to or lower than the set value, the constant voltage charge is terminated and the constant current charge is performed up to the second set voltage.

  Thereafter, constant voltage charging is performed with the second set voltage, and charging is completed when the current value becomes equal to or less than the set value. As a result, in the case of a battery having a shallow charging depth in the first cycle constant current charging, the second cycle constant current charging can be performed to achieve accurate charging in a short time to a sufficient depth. it can.

  At that time, if the time decay rate of the current obtained during the constant voltage charge in the first cycle is larger than the set value, the constant voltage charge at the first set voltage is continued. Thereby, in the case of a battery having a deep charging depth in the first cycle constant current charging, it is possible to perform an accurate charging without overcharging by shifting to a constant voltage charging.

  Moreover, it is preferable to change the setting value of the time decay rate of the current at the constant voltage charge in the first cycle depending on the temperature at which the battery is charged. In this case, since the electric characteristics of the battery differ depending on the temperature, an appropriate charging is performed by using an optimum set value at each temperature. By the way, when the temperature is higher than normal temperature, the internal resistance of the battery is lowered, so that the charging depth at a constant current is deepened. Therefore, the attenuation rate in constant voltage charging tends to increase, and it is better to set the predetermined value of the attenuation rate larger than that at room temperature. When the temperature is lower than normal temperature, the internal resistance of the battery increases, so that the charging depth at constant current becomes shallow. Therefore, the attenuation rate in constant voltage charging tends to be small, and it is better to set the predetermined value of the attenuation rate smaller than that at room temperature.

  Although FIG. 1 shows the case where the constant current + constant voltage charging is performed for two cycles, it may be repeated for three cycles or more. Further, the current values in the constant current charging in the first cycle and the second cycle are generally set to the same value, but may be different values.

  The secondary battery charging method of the present invention is useful as an optimal charging method that can be applied to individual batteries.

The flowchart which shows the charging method of this invention

Explanation of symbols

  None

Claims (3)

A charging method for a secondary battery that shifts to constant voltage charging after constant current charging,
When the first set voltage is reached by constant current charging, constant voltage charging is performed with the first set voltage, the time decay rate of the current at that time is obtained, and the second set voltage is reached based on the decay rate To determine whether or not constant current charging is possible,
A charging method for a secondary battery, wherein constant current charging is performed up to a second set voltage when possible, and then constant voltage charging is performed at a second set voltage. 2. The method of charging a secondary battery according to claim 1, wherein when it is impossible to determine whether or not constant current charging up to the second set voltage is possible, the constant voltage charge at the first set voltage is continued. The method for charging a secondary battery according to claim 1, wherein the time decay rate of the current is changed according to an environmental temperature of the battery.

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