JP5260904B2 - Charging method of lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase a charging capacity while protecting a lithium-ion secondary battery from a temperature, and fully charge the battery at high speed. <P>SOLUTION: The charging method of the lithium-ion secondary battery has a structure in which a battery 1 as a lithium-ion secondary battery is charged while comparing with a protective voltage (Vp) changing depending on the temperature, and charging is stopped when the voltage of the battery 1 exceeds the protective voltage (Vp) and the battery 1 is charged while switching the charging voltage (Vc) depending on a temperature zone. This charging method includes: starting charging at the highest charging voltage (Vc) first and detecting the temperature and voltage of the battery 1; when the voltage of the battery 1 exceeds the protective voltage (Vp) of the temperature zone detected from the temperature of the battery 1, stopping the charging; and, when the voltage falls due to the stop of charging, charging the battery at constant voltage/constant current using the charging voltage (Vc) for the temperature of the battery 1. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a method for charging a lithium ion secondary battery, and more particularly to a charging method for charging by changing a charging voltage depending on the temperature of the battery.

  The lithium ion secondary battery is charged with a constant current until the battery voltage rises to a constant voltage charging voltage, for example, 4.2V. Thereafter, when the constant current charging is continued, the battery voltage becomes abnormally high, so that the battery voltage is charged at a constant voltage with the charging voltage of 4.2V. In constant voltage charging, the charging current gradually decreases. When the charging current decreases to the minimum current, charging is stopped as a full charge.

The electrical characteristics of a lithium ion secondary battery change due to the influence of temperature. For this reason, if the constant voltage charging is performed at the same voltage as the normal temperature in a low temperature state, the lithium ion secondary battery is adversely affected. In order to eliminate this drawback, a charging method has been developed in which the charging voltage for constant voltage charging is changed depending on the temperature of the lithium ion secondary battery. (See Patent Document 1)
JP 2001-16795 A

  The lithium ion secondary battery can prevent adverse effects at low temperatures by changing the charging voltage for constant voltage charging according to the battery temperature. In this charging method, the temperature of a lithium ion secondary battery to be charged is detected, and the charging voltage for constant voltage charging is changed by the battery temperature. FIG. 1 shows voltage characteristics and current characteristics for charging a lithium ion secondary battery by this method. As shown in this figure, a low-temperature lithium ion secondary battery is initially charged at a constant voltage / constant current at a low charge voltage. A battery having a voltage lower than the charging voltage is initially charged with a constant current. Since constant current charging has a large charging current, the battery temperature increases with this charging current. When the temperature of the battery increases, the charging voltage for constant voltage charging is increased. In this state, the lithium ion secondary battery is charged with a constant voltage and a constant current at a high charge voltage. In this charging process, when the voltage of the battery rises to the charging voltage, the charging current is reduced by switching from constant current charging to constant voltage charging. In a battery in which the charging current decreases, the temperature rise due to the charging current is reduced and the battery temperature decreases. A battery whose battery temperature is lowered can be switched from a constant voltage charging voltage to a low charging voltage. However, since the battery voltage is higher than the charging voltage, charging is stopped at this timing. For this reason, the charging of the battery is interrupted in the middle, and a sufficient capacity cannot be charged. This problem can be solved by a charging method that does not decrease the charging voltage even when the battery temperature decreases, as shown by the dotted line in the figure, but this method charges a low-temperature battery at a high charging voltage. Reduce battery performance. As described above, when the charging voltage is lowered at a low temperature while protecting the battery, the lithium ion secondary battery cannot be charged with a sufficient capacity. That is, increasing the charging capacity of a low-temperature battery and battery protection are mutually contradictory characteristics, and it is difficult to satisfy both.

  The present invention has been developed for the purpose of solving this difficult problem. An important object of the present invention is to provide a method for charging a lithium ion secondary battery that can increase the charging capacity and can be fully charged quickly while ensuring the protection of the lithium ion secondary battery by temperature.

The lithium ion secondary battery charging method of the present invention has the following configuration in order to achieve the above-described object.
The charging method of the lithium ion secondary battery is that the battery 1 which is a lithium ion secondary battery is charged while being compared with the protection voltage (Vp) which changes depending on the temperature, and the voltage of the battery 1 exceeds the protection voltage (Vp). The charging is stopped and the charging voltage (Vc) is switched depending on the temperature band. In this charging method, charging is first started at the highest charging voltage (Vc), the temperature and voltage of the battery 1 are detected, and the protection voltage in the temperature band in which the voltage of the battery 1 is detected from the temperature of the battery 1 is detected. When (Vp) is exceeded, charging is stopped, and when charging is stopped and the voltage decreases, constant voltage / constant current charging is performed at a charging voltage (Vc) corresponding to the temperature of the battery 1.

  In the method for charging a lithium ion secondary battery according to claim 2 of the present invention, the protection voltage (Vp) is set such that the first protection voltage (Vp1) for stopping charging in the low temperature range and the charging in the standard temperature range are stopped. It is divided into a second protection voltage (Vp2) and a third protection voltage (Vp3) that stops charging in the high temperature range. Further, in this charging method, the charging voltage (Vc) is divided into a first charging voltage (Vc1) for charging the battery in the low temperature range, and a second charging voltage (Vc2) for charging the battery in the standard temperature range, The battery is partitioned into a third charging voltage (Vc3) for charging the battery in the high temperature range. The first charging voltage (Vc1) is equal to or lower than the first protection voltage (Vp1), the second charging voltage (Vc2) is equal to or lower than the second protection voltage (Vp2), and the third charging voltage (Vc3). Is less than or equal to the third protection voltage (Vp3). Further, the first protection voltage (Vp1) and the third protection voltage (Vp3) are set lower than the second protection voltage (Vp2).

  In the method for charging a lithium ion secondary battery according to claim 3 of the present invention, the first charging voltage (Vc1) is set lower than the third charging voltage (Vc3).

  In the method for charging a lithium ion secondary battery according to claim 4 of the present invention, the low temperature boundary temperature (T1) between the low temperature range and the standard temperature range is set to 5 ° C to 15 ° C. In the method for charging a lithium ion secondary battery according to claim 5 of the present invention, the high temperature boundary temperature (T2) between the standard temperature range and the high temperature range is set to 40 ° C to 50 ° C.

  According to the charging method of the lithium ion secondary battery of claim 6 of the present invention, the lithium ion secondary battery 1 is charged with the second protection voltage (Vp2) set to 4.25V.

  In the method for charging a lithium ion secondary battery according to claim 7 of the present invention, charging of the lithium ion secondary battery in the low temperature region or the high temperature region is started at the second charging voltage (Vc2).

  In the method for charging a lithium ion secondary battery according to claim 8 of the present invention, the charging voltage (Vc) is 0 to 100 mV lower than the protection voltage (Vp).

  According to the charging method of the lithium ion secondary battery of claim 9 of the present invention, when the temperature of the battery 1 being charged is changed from the low temperature range to the standard temperature range, the protection voltage (Vp) for stopping the charging is the first protection. The voltage rises from the voltage (Vp1) to the second protection voltage (Vp2).

  According to the charging method of the lithium ion secondary battery of claim 10 of the present invention, when the temperature of the battery 1 being charged is changed from the standard temperature range to the high temperature range, the protection voltage (Vp) for stopping the charging is the second protection. The voltage (Vp2) decreases to the third protection voltage (Vp3).

  The present invention is characterized in that the charge capacity can be increased while ensuring the protection by the temperature of the lithium ion secondary battery. The charging method of the present invention charges a battery that is a lithium ion secondary battery while comparing it with a protection voltage that changes depending on the temperature. When the battery voltage exceeds the protection voltage, the charging is stopped. In addition to charging by switching the charging voltage, charging is first started at the highest charging voltage to detect the battery temperature and voltage, and charging is performed when the battery voltage exceeds the protection voltage in the battery temperature band. This is because, when the voltage is reduced after that, the battery is charged at a constant voltage / constant current with a charging voltage corresponding to the temperature of the battery. In particular, the method for charging a lithium ion secondary battery according to the present invention is characterized in that charging is started at the highest charging voltage first, so that it can be fully charged in a short time. In addition, charging is resumed at a charging voltage corresponding to the temperature of the battery, and charging is stopped when the battery exceeds a protection voltage corresponding to the temperature, so that the battery can be charged to a sufficient capacity while protecting the battery.

  Further, the charging method according to claim 2 of the present invention includes a protection voltage for stopping charging when the voltage rises, a first protection voltage for stopping charging in a low temperature range, and a first protection voltage for stopping charging in a standard temperature range. 2 and a third protection voltage for stopping charging in the high temperature range, and further, the charging voltage is a first charging voltage equal to or lower than the first protection voltage for charging the battery in the low temperature range. And a second charging voltage equal to or lower than the second protection voltage for charging the battery in the standard temperature range, and a third charging voltage equal to or lower than the third protection voltage for charging the battery in the high temperature range, and In addition, the first protection voltage and the third protection voltage are set lower than the second protection voltage. According to this method, even when the temperature of the battery changes greatly from the low temperature range to the high temperature range, the battery can be charged to a sufficient capacity in a short time while protecting the battery.

  In particular, in the charging method of claim 3 of the present invention, in addition to the configuration of claim 2, the first charging voltage is made lower than the third charging voltage, so that the battery in the low temperature range is particularly effective. While protecting, the battery can be charged to a sufficient capacity.

  Furthermore, in the charging method according to claim 7 of the present invention, charging of the lithium ion secondary battery in the low temperature range or the high temperature range is started at the second charging voltage which is the highest charging voltage. This charging method starts charging the battery in the low temperature range and the high temperature range at the highest second charging voltage, so that it can be fully charged in a short time and the battery temperature changes to the low temperature range or the high temperature range. Even so, the battery can be charged while protecting the battery compared to the protection voltage.

  In the charging method according to claim 9 of the present invention, when the temperature of the battery being charged changes from the low temperature range to the standard temperature range, the protection voltage for stopping charging is changed from the first protection voltage to the second protection voltage. Since it rises and charges, it can be fully charged quickly while protecting the battery by increasing the protection voltage.

  Furthermore, in the charging method according to claim 10 of the present invention, when the temperature of the battery being charged is changed from the standard temperature range to the high temperature range, the protection voltage for stopping charging is changed from the second protection voltage to the third protection voltage. Therefore, even if the temperature of the battery being charged rises, it can be charged while protecting the battery.

  Embodiments of the present invention will be described below with reference to the drawings. However, the examples shown below exemplify the charging method of the lithium ion secondary battery for embodying the technical idea of the present invention, and the present invention describes the charging method of the lithium ion secondary battery as follows. Not specified for charging conditions. Further, this specification does not limit the members shown in the claims to the members of the embodiments.

  FIG. 2 is a block diagram of a charging circuit for charging a lithium ion secondary battery. The charging circuit in this figure includes a power supply circuit 2 for charging the lithium ion secondary battery 1 at a constant voltage / constant current, a control circuit 3 for controlling a state in which the power supply circuit 2 charges the lithium ion secondary battery 1, A voltage detection circuit 6 that detects and inputs the voltage of the battery 1 to the control circuit 3, a current detection circuit 5 that detects a charging current of the battery 1, and a temperature detection circuit 4 that detects and outputs the temperature of the battery. .

  The power supply circuit 2 is a switching power supply. Although not shown, the switching power supply switches direct current obtained by rectifying AC 100V, which is a commercial power supply, to the switching element and inputs it to the primary side of the transformer. The AC output on the secondary side of the transformer is rectified to output the battery charging voltage. This switching power supply controls an output voltage, that is, a charging voltage with a duty for switching the switching element on and off. The on-time of the switching element is lengthened to increase the charging voltage, and the on-time is shortened to lower the charging voltage. Since the power supply circuit 2 charges the lithium ion secondary battery 1 at a constant voltage / constant current, a voltage feedback circuit for controlling the charging voltage to be constant and a current feedback circuit for limiting the maximum value of the output current to be constant Connected to the input circuit. The voltage feedback circuit controls the duty of the switching element via the input circuit to control the output voltage to a charging voltage specified by the battery temperature.

  The voltage detection circuit 6 detects the voltage of the battery 1 at a predetermined sampling period, converts the detected voltage into a digital signal, and inputs the digital signal to the control circuit 3. The current detection circuit 5 detects the charging current of the battery 1 at a predetermined sampling period, converts the detected current into a digital signal, and inputs the digital signal to the control circuit 3. Furthermore, the temperature detection circuit 4 detects the surface temperature of the battery at a predetermined sampling period, converts the detected temperature into a digital signal, and inputs the digital signal to the control circuit 3.

  The control circuit 3 stores the protection voltage (Vp) corresponding to the temperature of the battery 1 and the charging voltage (Vc), and controls the battery 1 to a constant voltage based on the data stored in the storage circuit 7. And an arithmetic circuit 8 for calculating a charging voltage (Vc) for constant current charging.

  FIG. 3 shows the protection voltage (Vp) and the charging voltage (Vc) stored in the memory circuit 7. The storage circuit 7 stores a protection voltage (Vp) for stopping charging in the protection voltage storage unit 11, and stores a charging voltage (Vc) for charging the battery at a constant voltage in the charging voltage storage unit 12. The storage circuit 7 storing the data of FIG. 3 divides the temperature band of the battery to be charged into a low temperature range, a standard temperature range, and a high temperature range, and provides a protection voltage ( Vp) and charging voltage (Vc) are stored. The low temperature boundary temperature (T1) between the low temperature region and the standard temperature region is, for example, 10 ° C. However, the low temperature boundary temperature (T1) between the low temperature region and the standard temperature region may be 5 ° C to 15 ° C. The high temperature boundary temperature (T2) between the standard temperature range and the high temperature range is, for example, 45 ° C. However, the high temperature boundary temperature (T2) between the standard temperature range and the high temperature range may be 40 ° C to 50 ° C.

  The first protection voltage (Vp1) stored in the protection voltage storage unit 11 for stopping the charging of the battery in the low temperature range is higher than the second protection voltage (Vp2) for stopping the charging of the battery in the standard temperature range. It is low. Further, the third protection voltage (Vp3) for stopping the charging of the battery in the high temperature range is set lower than the second protection voltage (Vp2). Furthermore, the first protection voltage (Vp1) is lower than the third protection voltage (Vp3).

  The first protection voltage (Vp1) and the third protection voltage (Vp3) are specified based on the second protection voltage (Vp2). The second protection voltage (Vp2) is set to an optimum voltage value for the type of the lithium ion secondary battery. For example, in the case of a lithium cobalt oxide-carbon type lithium ion secondary battery, preferably 4. Set to 25V. However, in this type of lithium ion secondary battery, the second protection voltage (Vp2) can be set to 0 to 20 mV lower than 4.25V, and if the type of the lithium ion secondary battery is different, The second protection voltage (Vp) is set to the optimum voltage.

  In addition, the second protection voltage (Vp2) can be set to an optimum value in consideration of the sampling period for detecting the battery voltage. If the sampling period for detecting the voltage is short, the second protection voltage (Vp2) can be set high, for example, 4.25V. This is because when the sampling period is short, the time during which the battery voltage exceeds the second protection voltage (Vp2) can be shortened. The second protection voltage (Vp2) can be increased to increase the charging capacity of the battery, and can be decreased to improve the safety of the battery. The sampling cycle in which the voltage detection circuit 6 detects the battery voltage is preferably set to 20 μsec or less. The charging method that detects the voltage of the battery at this sampling period and stops charging when the battery voltage exceeds the protection voltage can reduce the time for the battery to exceed the protection voltage to 20 μsec or less. In this charging method, the second protection voltage (Vp2) is increased to, for example, 4.25 V, and the time for the battery voltage to exceed the second protection voltage (Vp2) can be shortened to 20 μsec or less. When the sampling period becomes longer, the time for the battery to exceed the protection voltage becomes longer. Therefore, the second protection voltage (Vp2) is lower than 4.25V, for example, 5 mV to 30 mV lower than 4.25V. However, it is also possible to charge the battery while protecting the battery more safely by shortening the sampling period and lowering the second protection voltage (Vp2).

  The charging method of the present invention starts charging at the highest charging voltage. In the method of dividing the battery temperature band into three bands, a low temperature range, a standard temperature range, and a high temperature range, the second protection voltage (Vp2) and the second charge voltage (Vc2) in the standard temperature range are Highest. In this charging method, when charging the battery with the second charging voltage (Vc2) with the charging voltage (Vc) lower than the protection voltage (Vp), the voltage of the battery becomes the second protection voltage (Vp2). Never exceed. This is because the battery voltage does not exceed the charging voltage (Vc) and the charging voltage (Vc) is lower than the protection voltage (Vp). Therefore, when one lithium ion secondary battery is charged with the second charging voltage (Vc2), the voltage of this battery does not exceed the second protection voltage (Vp2). For this reason, the lithium ion secondary battery in the standard temperature range does not stop charging when the voltage exceeds the second protection voltage (Vp2). However, when an assembled battery in which a plurality of lithium ion secondary batteries are connected in series is charged at a constant voltage / constant current, the voltage of the high voltage battery with the highest voltage is the second protection due to the battery imbalance. The voltage (Vp2) may be exceeded.

  A charging voltage for charging an assembled battery in which a plurality of lithium ion secondary batteries are connected in series is a voltage that is an integral multiple of the number of batteries connected in series. For example, the charging voltage (Vc) of an assembled battery in which three lithium ion secondary batteries are connected in series is three times the charging voltage (Vc) of one lithium ion secondary battery. In the assembled battery charged in this state, the voltage of each battery is detected and compared with the protection voltage (Vp). Therefore, the protection voltage (Vp) of each battery is not tripled and becomes the same voltage as the protection voltage (Vp) for charging one battery. For example, when an assembled battery in which three batteries are connected in series is charged with a second protection voltage (Vp2) of 4.25V and a second charging voltage (Vc2) of 4.23V, charging is performed. The voltage (Vc) is 12.69V (4.23V × 3), and the second protection voltage (Vp2) of each battery is 4.25V. In the assembled battery charged in this state, the voltages of all the batteries cannot be made exactly the same voltage. Due to battery imbalance, there is a difference in the voltage of each battery. Therefore, the voltage of the battery with the highest voltage may exceed the second protection voltage (Vp2). Therefore, in the battery charging method, the battery is charged when the voltage of any battery exceeds the protection voltage (Vp). To stop.

  The charging method of the present invention includes a method for charging an assembled battery in which a plurality of batteries are connected in series without specifying the number of serially connected lithium ion secondary batteries to be charged. Therefore, in the method of charging an assembled battery in which series batteries are connected in series, the protection voltage (Vp) of each battery is the same, and the number of batteries in which the charging voltage (Vc) is connected in series is the same. Integer multiple. Therefore, in the present specification, “to make the charging voltage (Vc) lower than the protection voltage (Vp)” means the charging voltage (Vc) in the method of charging an assembled battery in which a plurality of batteries are connected in series. In the charging method of the assembled battery in which three batteries are connected in series, for example, 1/3 of the charging voltage (Vc) of the assembled battery is the protective voltage. It means that it is lower than (Vp).

  The first protection voltage (Vp1) is set 30 mV to 300 mV lower than the second protection voltage (Vp2), for example, 4.05V. The third protection voltage (Vp3) is set lower than the second protection voltage (Vp2) and higher than the first protection voltage (Vp1). Therefore, the voltage difference between the third protection voltage (Vp3) and the second protection voltage (Vp2) is, for example, 30% of the voltage difference between the second protection voltage (Vp2) and the first protection voltage (Vp1). Or 80%, for example, 4.15V.

  The charging voltage storage unit 12 includes a first charging voltage (Vc1) set to be equal to or lower than the first protection voltage (Vp1) and a second charging voltage set to be equal to or lower than the second protection voltage (Vp2). (Vc2) and the third charging voltage (Vc3) set below the third protection voltage (Vp3) are stored. The charging voltage (Vc) in each temperature band is set to a voltage 30 mV lower than the protection voltage (Vp) in each temperature band, for example. However, the charging voltage (Vc) in each temperature band can be set to a voltage 0 mV to 50 mV lower than the protection voltage (Vp) in each temperature band.

  The control circuit 3 detects the voltage, current, and temperature of the battery at a predetermined sampling period, and controls the state of charge of the lithium ion secondary battery 1. The control circuit 3 starts charging at the highest charging voltage (Vc) first. The control circuit 3 detects the battery temperature and voltage at a predetermined sampling period while charging the battery. When the voltage of the battery exceeds the protection voltage (Vp) in the temperature band detected, the control circuit 3 switches off the switching element and stops charging. The voltage of the battery decreases when charging is stopped. When the voltage of the battery drops to a voltage that can be charged with the charging voltage (Vc) corresponding to the temperature, the control circuit 3 switches the charging voltage (Vc) to the charging voltage corresponding to the temperature of the battery to determine the battery. Fully charge by charging with voltage and constant current. The full charge of the battery is determined by detecting that the charging current has been reduced to the minimum current by the current detection circuit 5.

  4 to 7 show the battery voltage, the charging voltage (Vc), the charging current, and the protection voltage (in the state where the lithium ion secondary battery in the standard temperature range, the low temperature range, and the high temperature range is charged. It is a graph which shows the state from which Vp) changes.

  FIG. 4 shows the state of charge of the battery in which the temperature is in the standard temperature range from the start of charging until the battery is fully charged. As shown in this figure, charging is started at the second charging voltage (Vc2) having the highest voltage. Since this battery has the highest protection voltage (Vp) at the second protection voltage (Vp2), the voltage of the battery does not exceed the second protection voltage (Vp2) and the second charging voltage (Vc2). ) Is fully charged with constant voltage / constant current charging.

  FIG. 5 shows a state of charge of the battery in which the temperature is set to a low temperature range from the start of charging until the battery is fully charged. As shown in this figure, this battery is also charged with the second charging voltage (Vc2) which is the highest voltage. Since this battery is at the first protection voltage (Vp1) having the lowest protection voltage (Vp), charging is stopped when the voltage of the battery exceeds the first protection voltage (Vp1). When charging is stopped and the battery voltage drops to the charging resumption voltage (Va), constant voltage / constant current charging is performed at the first charging voltage (Vc1) which is the charging voltage in the low temperature range which is the battery temperature range. Fully charged.

  The charge resumption voltage (Va) at this time is lower than the protection voltage (Vp) in the battery temperature band after charging is stopped, for example, the first protection voltage (Vp1) for a battery in a low temperature range. ) Set to a lower voltage. Therefore, the charging resumption voltage (Va) in this charging method is a voltage lower than the first protection voltage (Vp1), a voltage lower than the first charging voltage (Vc1), or a first charging voltage (Vc1). ) Is set to a voltage lower than the first set voltage that is set lower than the first set voltage. This charge resumption voltage (Va) can be specified by a table stored in the storage circuit as a voltage corresponding to the temperature band of the battery, for example. The charge resumption voltage (Va) can also be calculated as a voltage set lower by a predetermined voltage from the protection voltage (Vp) and the charge voltage (Vc) corresponding to the battery temperature band.

  FIG. 6 shows a state of charge of the battery in which the temperature is set to a high temperature range until charging is started and fully charged. As shown in this figure, this battery is also charged at the second charging voltage (Vc2) which is the highest voltage. Since this battery is at the third protection voltage (Vp3) whose protection voltage (Vp) is lower than the second protection voltage (Vp2), it is charged when the battery voltage exceeds the third protection voltage (Vp3). Is stopped. When charging is stopped and the battery voltage becomes lower than the charging resumption voltage (Va), the battery is fully charged by constant voltage / constant current charging with the third charging voltage (Vc3) which is the charging voltage in the high temperature range. To do.

  The charge resumption voltage (Va) at this time is a voltage lower than the protection voltage (Vp) in the battery temperature band after the battery voltage exceeds the third protection voltage (Vp3) and stops charging. In the battery in the temperature range, the voltage is set lower than the third protection voltage (Vp3). Therefore, the charge resumption voltage (Va) in this charging method is a voltage lower than the third protection voltage (Vp3), a voltage equal to or lower than the first protection voltage (Vp1) or the first charge voltage (Vc1), or The voltage is set to be lower than the third set voltage which is set lower than the third charge voltage (Vc3).

  FIG. 7 shows a state in which charging is performed in a state where the temperature of the battery that has started charging changes between a standard temperature range and a high temperature range. As shown in this figure, this battery is also charged at the second charging voltage (Vc2) which is the highest voltage. In this battery, the temperature of the battery rises due to a charging current in a constant current state, and rises from a standard temperature range to a high temperature range. As the battery temperature rises, the protection voltage (Vp) decreases from the second protection voltage (Vp2) to the third protection voltage (Vp3). Therefore, charging is stopped when the voltage of the battery exceeds the third protection voltage (Vp3). When the charging is stopped, the heat generated by the charging current disappears and the temperature of the battery decreases, so that the temperature is changed from the high temperature range to the standard temperature range. When the battery reaches the standard temperature range, the protection voltage (Vp) rises to the second protection voltage (Vp2). In this state, the battery voltage becomes a charge resumption voltage (Va) lower than the protection voltage (Vp) in the temperature band, so that charging is resumed. When charging is resumed and the temperature of the battery rises due to the charging current and becomes a high temperature range again, the protection voltage (Vp) decreases to the third protection voltage (Vp3). In this state, when the voltage of the battery exceeds the third protection voltage (Vp3), charging is stopped again. When charging is stopped and the battery temperature falls from the high temperature range to the standard temperature range, the protection voltage (Vp) rises again to the second protection voltage (Vp2). Therefore, the battery voltage becomes a charging resumption voltage (Va) lower than the second protection voltage (Vp2), and charging is resumed. Thereafter, the charging current gradually decreases and heat generation due to the charging current is reduced. Therefore, the temperature of the battery is not raised from the standard temperature range to the high temperature range, and is fully charged by constant voltage / constant current charging at the second charging voltage (Vc2).

  The charging circuit of FIG. 2 charges the lithium ion secondary battery in steps based on the flowchart shown in FIG.

[Step of n = 1]
First, charging is started at the highest charging voltage (Vc).
[Steps n = 2, 3]
It is determined whether the charging current (I) has become smaller than the minimum current (Imin). The minimum current (Imin) is set to a charging current when the assembled battery 1 is fully charged. Therefore, when the charging current (I) of the assembled battery 1 becomes smaller than the minimum current (Imin), it is determined that the battery is fully charged, and the process proceeds to step n = 3 and the charging is terminated.
[Step n = 4]
If the charging current (I) has not decreased to the minimum current (Imin), the temperature detection circuit 4 detects the temperature of the battery 1 in this step, and the protection voltage storage unit of the storage circuit 7 is detected from the detected battery temperature. 11 is used to detect a protection voltage (Vp) in the temperature band.
[Steps n = 5, 6]
It is determined whether the battery voltage (E) exceeds the protection voltage (Vp). When the battery voltage (E) exceeds the protection voltage (Vp), the process proceeds to step n = 6 and charging is stopped. If the battery voltage (E) does not exceed the protection voltage (Vp), the process returns to the step of n = 2 and charging is continued.
After that, n = 2, 4 until the charging current (I) decreases to the minimum current (Imin) and the charging is finished, or until the battery voltage (E) exceeds the protection voltage (Vp) and the charging is stopped. And loop 5 steps.
[Step n = 7]
When the battery voltage (E) exceeds the protection voltage (Vp) and charging is stopped, the temperature detection circuit 4 detects the temperature of the battery 1, and the charge resumption voltage (Va) in the temperature band corresponding to the detected battery temperature. ) Is detected.
[Step n = 8]
It is determined whether or not the battery voltage (E) has decreased to the charging restart voltage (Va). Until the battery voltage (E) drops to the charge resumption voltage (Va), the steps of n = 7 and 8 are looped and held in the charge stop state.
[Step n = 9]
When the battery voltage (E) decreases to the charge resumption voltage (Va), the temperature detection circuit 4 detects the temperature of the battery 1 and the data stored in the charging voltage storage unit 12 of the storage circuit 7 from the detected battery temperature. Based on this, the charging voltage (Vc) in the temperature band is detected.
[Step n = 10]
Charging is resumed at the charging voltage (Vc) in the temperature band specified from the battery temperature, and the process returns to the step of n = 2.
Thereafter, the battery 1 is charged by looping the steps of n = 2 and 4 to 10 until the charging current (I) becomes the minimum current (Imin). When the charging current (I) becomes smaller than the minimum current (Imin), it is determined that the battery is fully charged, and the process proceeds to the step of n = 3 and the charging is finished.

It is a graph which shows the characteristic of the voltage and electric current of the battery charged with the conventional charging method. It is a block diagram which shows an example of the charging circuit used for the charging method of the lithium ion secondary battery concerning one Example of this invention. It is a graph which shows the protection voltage with respect to battery temperature, and a charging voltage. It is a graph which shows an example of the change of the protection voltage in the state which charges a lithium ion secondary battery with the charging method of this invention, a charging voltage, a battery voltage, and a charging current. It is a graph which shows another example of the change of the protection voltage in the state which charges a lithium ion secondary battery with the charging method of this invention, a charging voltage, a battery voltage, and a charging current. It is a graph which shows another example of the change of the protection voltage in the state which charges a lithium ion secondary battery with the charging method of this invention, a charging voltage, a battery voltage, and a charging current. It is a graph which shows another example of the change of the protection voltage in the state which charges a lithium ion secondary battery with the charging method of this invention, a charging voltage, a battery voltage, and a charging current. 3 is a flowchart illustrating a method for charging a lithium ion secondary battery according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Power supply circuit 3 ... Control circuit 4 ... Temperature detection circuit 5 ... Current detection circuit 6 ... Voltage detection circuit 7 ... Memory circuit 8 ... Arithmetic circuit 11 ... Protection voltage memory | storage part 12 ... Charging voltage memory | storage part

Claims (10)

The battery, which is a lithium ion secondary battery, is charged in comparison with the protection voltage (Vp) that changes depending on the temperature. When the battery voltage exceeds the protection voltage (Vp), the charging is stopped and the charging voltage ( Vc) is a method of charging by switching,
Charging is started at the highest charging voltage (Vc) first, and the battery temperature and voltage are detected. When the battery voltage exceeds the protection voltage (Vp) in the temperature band detected from the battery temperature, charging is performed. A charging method for a lithium ion secondary battery, characterized in that when the voltage is lowered by stopping and charging, the battery is charged at a constant voltage / constant current at a charging voltage (Vc) corresponding to the temperature of the battery. The protection voltage (Vp) is the first protection voltage (Vp1) that stops charging in the low temperature range, the second protection voltage (Vp2) that stops charging in the standard temperature range, and the charging is stopped in the high temperature range. Divided into a third protection voltage (Vp3),
Further, the charging voltage (Vc) is a first charging voltage (Vc1) equal to or lower than a first protection voltage (Vp1) for charging the battery 1 in the low temperature range, and a second charging voltage (Vc1) for the battery 1 in the standard temperature range. A second charging voltage (Vc2) below the protection voltage (Vp2) and a third charging voltage (Vc3) below the third protection voltage (Vp3) for charging the battery 1 in the high temperature range; The method for charging a lithium ion secondary battery according to claim 1, wherein the first protection voltage (Vp1) and the third protection voltage (Vp3) are lower than the second protection voltage (Vp2).   The method for charging a lithium ion secondary battery according to claim 2, wherein the first charging voltage (Vc1) is lower than the third charging voltage (Vc3).   The method for charging a lithium ion secondary battery according to claim 2, wherein a low temperature boundary temperature (T1) between the low temperature region and the standard temperature region is 5 ° C to 15 ° C.   The method for charging a lithium ion secondary battery according to claim 2, wherein the high temperature boundary temperature (T2) between the standard temperature range and the high temperature range is 40 ° C to 50 ° C.   The method for charging a lithium ion secondary battery according to any one of claims 2 to 5, wherein the lithium ion secondary battery is charged with the second protection voltage (Vp2) set to 4.25V.   The method for charging a lithium ion secondary battery according to any one of claims 2 to 6, wherein charging of the lithium ion secondary battery in a low temperature range or a high temperature range is started at the second charging voltage (Vc2).   The method for charging a lithium ion secondary battery according to claim 1 or 2, wherein the charging voltage (Vc) is 0 to 100 mV lower than the protective voltage (Vp).   The protection voltage (Vp) for stopping charging rises from the first protection voltage (Vp1) to the second protection voltage (Vp2) when the temperature of the battery being charged changes from a low temperature range to a standard temperature range. 2. A method for charging a lithium ion secondary battery described in 2.   The protection voltage (Vp) for stopping charging is lowered from the second protection voltage (Vp2) to the third protection voltage (Vp3) when the temperature of the battery being charged is changed from the standard temperature range to the high temperature range. 2. A method for charging a lithium ion secondary battery described in 2.

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