Method and apparatus for charging rechargeable cells
A method for charging rechargeable cells, in particular lithium ion cells. An apparatus for charging such cells. In order to specify a method for charging a lithium-based cell and an apparatus for charging a lithium-based cell, in which the capacitance of the cell is optimally used, the charging time is drastically shortened, the shelf life of the cell is extended and/or it is possible to increase the capacitance of the cell, a method is stated which includes the following steps, pulsed charging of the cell, wherein the charging current I L exceeds the nominal charging current I Lmax of the cell during the charging pulses; and the cell is discharged between the charging pulses using load pulses.
1. A method for charging a lithium-ion based rechargeable cell, comprising:
pulsed charging the cell, wherein a charging current I L , during the charging pulses, exceeds a maximal nominal charging current I Lmax of the cell by up to 5-times; and
discharging the cell between the charging pulses by load pulses, wherein the load pulses are shorter than the charging pulses, and
measuring a voltage U z of the cell during each load pulse;
checking whether the measured voltage U z of the cell is equal or greater than an end-of-charge voltage U Lmax of the cell;
finishing charging of the cell after the measured voltage U z of the cell at each of a predefined number of load pulses (n) corresponds to an end-of-charge voltage U Lmax of the cell, wherein n is greater than or equal to 1,
wherein a level of the charging current I L varies in consecutive charging pulses.
2. The method according to claim 1 , wherein the charging current I L , during the charging pulses, is more than 1.5 times the maximal nominal charging current I Lmax of the cell.
3. The method according to claim 2 , wherein the charging current I L is twice the maximal nominal charging current I Lmax or greater.
4. The method according to claim 1 , wherein a level of the charging current I L , during the charging pulses and/or a height of the load pulses is dependent on a state of the cell.
5. The method according to claim 4 , wherein the level of the current during the charging pulses and/or the load pulses is set depending on an internal resistance of the cell and/or a temperature of the cell.
6. The method according to claim 1 , wherein a discharging current I Last is a maximum of 20-25 % of the maximal nominal charging current I Lmax flows during a load pulse.
7. The method according to claim 1 , a level of a discharging current I Last varies in consecutive load pulses.
8. The method according to claim 1 , wherein on exceeding a predetermined voltage of the cell, the charging operation is terminated and/or wherein on exceeding a predetermined temperature (T max ) of the cell the charging operation is terminated.
9. The method according to claim 1 , wherein depending on the measured voltage, a level of the charging current I L is set for the subsequent charging pulse, wherein if the measured voltage U z of the cell lies above a predefined value during the load pulse, the charging current I L is reduced in the next charging pulse.
10. The method according to claim 1 , wherein depending on the measured voltage, the level of a discharging current I Last is set for the subsequent load pulse, wherein if the measured voltage U z of the cell lies above a predefined value during the load pulse, the discharging current I Last is reduced in the next load pulse.
11. The method according to claim 1 , where a length of a load pulse corresponds to about one-half of a length of a charging pulse.
12. The method according to claim 1 , wherein if the measured voltage U z of the cell reaches the end-of-charge voltage U Lmax during a load pulse, the charging current I L is reduced in the next charging pulse.
13. A device for charging a lithium-ion based rechargeable cell, comprising a controller configured to:
pulse charge the cell, wherein a charging current I L , during the charging pulses, exceeds a maximal nominal charging current I Lmax of the cell by up to 5-times: and
discharge the cell between the charging pulses by load pulses, wherein the load pulses are shorter than the charging pulses, and
finish charging of the cell after a measured voltage UZ at each of a predefined number of load pulses (n) corresponds to an end of-charge voltage U Lmax of the cell, wherein n is greater than or equal to 1,
wherein a level of the charging current I L varies in consective charging pulses.
14. The device according to claim 13 , further comprising a device for providing a sink in order to discharge the cell during the load pulses, wherein a size of the load pulse can be set.
15. The device according to claim 13 , further comprising at least one capacitor to provide the load pulse and/or the charging pulse.