Charging of a Battery Cell

Abstract

A method for charging a battery cell is provided. During a charging phase at a constant charging current, monitoring is carried out to ascertain whether a charging voltage applied to the battery cell reaches or exceeds a predefined switchover voltage, and, if this is the case, a switchover is made to the next charging phase at a lower constant charging current. During the charging phases, additional monitoring is carried out to ascertain whether the difference between the charging voltage and the switchover voltage of this charging phase reaches or falls below a predefined value, and, if so, at least one discharge pulse is applied to the battery cell.

Claims

1.-15. (canceled)

16. A method for charging a battery cell in charging phases, the method comprising: during a charging phase with a charging current that is at least approximately constant, performing monitoring to determine whether a charging voltage applied to the battery cell reaches or exceeds a predefined changeover voltage and, if the charging voltage applied to the battery cell reaches or exceeds the predefined changeover voltage, performing a changeover to a next charging phase with a lower charging current that is at least approximately constant, and during each charging phase of the charging phases, performing additional monitoring to determine whether a predefined difference between the charging voltage and the changeover voltage of the charging phase is reached or fallen below, and, if the predefined difference between the charging voltage and the changeover voltage of the charging phase is reached or fallen below, applying at least one discharge pulse to the battery cell.

17. The method according to claim 16, wherein a duration of the at least one discharge pulse is in a range between 0.1 s and 10 s.

18. The method according to claim 17, wherein the range is between 0.5 s and 2 s.

19. The method according to claim 16, wherein the at least one discharge pulse has an amplitude absolute value that does not fall below a value C/10 of a C rate of the battery cell.

20. The method according to claim 16, wherein an amount of discharge that is output to the battery cell by the at least one discharge pulse during the charging phase, when summed, does not exceed 5% of the amount of charge of the charging phase.

21. The method according to claim 20, wherein the amount of discharge that is output to the battery cell by the at least one discharge pulse during the charging phase, when summed, does not exceed 1% of the amount of charge of the charging phase.

22. The method according to claim 21, wherein the amount of discharge that is output to the battery cell but the at least one discharge pulse during the charging phase, when summed, is between 0.1% and 1% of the amount of charge of the charging phase.

23. The method according to claim 16, wherein during a charging phase of the charging phases, a plurality of discharge pulses are applied to the battery cell in a temporally spaced-apart manner when the difference is reached or fallen below.

24. The method according to claim 23, wherein following a first discharge pulse, a further discharge pulse is applied if the charging voltage has increased by a predefined additional voltage value after having reached the difference.

25. The method according to claim 16, wherein the difference corresponds to a critical threshold value of an anode voltage of the battery cell.

26. The method according to claim 16, in which the difference is constant for all of the charging phases.

27. The method according to claim 16, wherein the difference is different for at least two of the charging phases.

28. The method according to claim 16, wherein a lithium-based battery cell is charged.

29. The method according to claim 28, wherein the lithium-based battery cell is a lithium battery cell.

30. The method according to claim 16, in which a plurality of battery cells are combined to form a battery pack.

31. The method according to claim 30, wherein the monitoring is performed individually for each battery cell of the battery pack to determine whether the difference has been reached or fallen below, and at least one discharge pulse is applied to the battery pack as soon as one battery cell reaches or falls below the difference.

32. A battery charging apparatus that is configured to perform the method according to claim 16.

33. A vehicle comprising at least part of the battery charging apparatus according to claim 32.

34. A charging station for a vehicle, the charging station comprising at least part of the battery charging apparatus according to claim 32.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG. 1 shows, in the form of a sketch and not to scale, three plots of charging parameters, which describe an MSCC charging operation, against time in minutes, as yet without discharge pulses.

[0051] FIG. 2 shows a possible flowchart for carrying out the method.

[0052] FIG. 3 shows, in the form of a sketch and not to scale, a plot of a current, flowing to and from a battery cell, during a charging phase following the associated trigger voltage being reached, with discharge pulses.

DETAILED DESCRIPTION OF THE DRAWINGS

[0053] FIG. 1 shows plots of typical charging parameters of an MSCC charging operation against time t in minutes for a lithium-ion battery cell as yet without discharge pulses, specifically the charging current I.sub.L in amperes for a plurality of charging phases LP1, LP2 and LP3 in an upper plot, the charging voltage U.sub.L, applied to the same battery cell, in volts, in a middle plot, and the associated anode voltage U.sub.A in volts in a lower plot.

[0054] With respect to the upper plot, the charging phases LP1, LP2, LP3 have a charging current I.sub.L that in each case is constant but gradually decreasing for successive charging phases LP1, LP2, LP3, for example I.sub.L=125 A during LP1, I.sub.L=90 A during LP2 and I.sub.L=75 A during LP3, etc. The changeover time between LP1 and LP2 is referred to as t1 and the changeover time between LP2 and LP3 is referred to as t2. At the changeover times t1 and t2, the associated charging current I.sub.L is decreased in a stepped manner.

[0055] The middle plot shows that the charging voltage U.sub.L, which is needed for maintaining a constant charging current I.sub.L, typically increases continuously for a respective charging phase LP1 to LP3 after initially decreasing for a short time following a changeover between two charging phases LP1, LP2 or LP2, LP3. The changeover is triggered or carried out when the charging voltage U.sub.L of a charging phase LP1 to LP3 reaches a respective changeover voltage U.sub.U. The changeover voltages U.sub.U can in particular be selected in such a way that they are greater for each following charging phase LP1, LP2, LP3. This is generally expedient, since the charging voltage U.sub.L of a following charging phase LP2, LP3 exceeds the changeover voltage U.sub.U of the preceding charging phase LP1 or LP2 comparatively quickly. By way of example, it may be the case that U.sub.U (LP1)=3.95 V, U.sub.U (LP2)=4.00 V and U.sub.U (LP3)=4.05 V.

[0056] The lower plot shows that the anode voltage U.sub.A measured overall against Li/Li.sup.+, for example, decreases during each of the charging phases LP1 to LP3. If the anode voltage U.sub.A were to become negative in the course of the charging phase LP1, LP2, LP3, plating would occur. The overall anode voltage U.sub.A is therefore kept as a positive value during the charging operation. However, on account of inhomogeneities, shape, etc. of the anode, a local deviation from the overall measured anode voltage U.sub.A can arise, wherein a negative anode voltage can occur locally even if the overall measured anode voltage U.sub.A is still positive. For the present method, it is therefore assumed that the risk of local plating noticeably increases even when a positive critical anode voltage U.sub.A,krit is reached or fallen below.

[0057] This critical anode voltage U.sub.A,krit is reached at a time t.sub.SE, and a trigger voltage U.sub.SE for triggering or initiating at least the first discharge pulse P0, in particular the discharge pulses P0 to P9 (see FIG. 3), is advantageously set in such a way that the charging voltage U.sub.L likewise reaches this trigger voltage U.sub.SE at least approximately at the time t.sub.SE. In other words, the trigger voltage U.sub.SE is selected such that it coincides with the critical anode voltage U.sub.A,krit being reached. This means that discharge pulses P0 to P9 preventing plating are injected or applied only when it is necessary, specifically if the anode voltage U.sub.A enters the voltage range U.sub.A≤U.sub.A,krit that is critical for the plating. The application of discharge pulses P0 to P9 that increase the charging time of the battery cell to time or voltage ranges t<t.sub.SE or U.sub.A>U.sub.A,krit that are uncritical for the plating is therefore avoided in a targeted manner. Thought is also given to the fact that, to achieve a short charging time, the changeover of a charging phase LP1 to LP3 is advantageously delayed for as long as possible, which also means that the anode voltage U.sub.A should be brought as close as possible to U.sub.A=0. This objective can be largely achieved, without producing plating, through the use of the discharge pulses P0 to P9, also taking inhomogeneities, shape, etc. of the anode into consideration.

[0058] FIG. 2 shows a possible flowchart for carrying out the method be implemented in a battery charging apparatus BV. The battery charging apparatus BV can constitute a part or component of a vehicle F and/or a charging station LSt. FIG. 3 shows a corresponding plot of the current I, flowing to and from the battery cell, against time t for the first charging phase LP1.

[0059] In a step S1, a charging phase LP1 is started at the beginning of a charging operation, for example.

[0060] Then, monitoring is carried out in step S2 to determine whether the difference ΔU between the changeover voltage U.sub.U and the applied charging voltage U.sub.L is reached or fallen below, or whether the charging voltage U.sub.L has reached or exceeded the trigger voltage U.sub.SE=U.sub.U−ΔU.

[0061] If this is the case (“Y”), in a step S3, a first discharge pulse P0 of, for example, a duration between 0.1 s and 10 s is injected, as also shown in FIG. 3.

[0062] Following the end of the first discharge pulse P0, monitoring is carried out in step S4 to determine whether the charging voltage U.sub.L has reached the changeover voltage U.sub.U. If this is the case (“Y”), there is a changeover to a following charging phase LP1, LP2, LP3 or a new charging phase LP1, LP2, LP3 is begun.

[0063] If this is not the case (“N”), monitoring is carried out in step S5 to determine whether the charging voltage U.sub.L has reached the trigger voltage U.sub.SE plus an nth additional voltage value U.sub.Z,n, wherein n is the number of the additional (second, etc.) discharge pulses P1 to P9. Monitoring is therefore carried out to determine whether U.sub.L≥U.sub.SE+U.sub.Z,n. If the discharge pulses P1 to P9 are intended to be triggered equidistantly with respect to the voltage, the trigger condition can also be described as U.sub.L≥U.sub.SE+n.Math.U.sub.Z, wherein n=1 for the first additional discharge pulse.

[0064] If this is the case (“Y”), a further nth discharge pulse P1 to P9 is applied in step S6 and, following the end of this, in step S7 there is a branch back to step S4, with n being incremented (n≈n+1). In the present case, nine further discharge pulses P1 to P9 are applied, for example.

[0065] This sequence is carried out until the charging operation is interrupted or ended.

[0066] As shown in FIG. 3, the discharge pulses P1 to P9 can have the same pulse duration, e.g. of 1 s, and/or can have the same discharge current amplitude, e.g. corresponding to a value of the C rate of the battery cell. If the inherent C rate of a battery cell is C h.sup.−1, a discharge current I.sub.SE is advantageously set to I.sub.SE≤−C/10, in this case particularly advantageously to I.sub.SE=−C amperes. By way of example, the discharge current can be I.sub.SE=−60 A. In particular, the amount of charge that is discharged by injecting the discharge pulses P0 to P9 collectively during the associated charging phase LP1 is at least 0.1% of the amount of charge of the associated charging phase LP1 and/or does not exceed 2% of the amount of charge.

[0067] For example, it may be the case that ΔU=10 mV, while, for example, it may be the case that U.sub.Z=1 mV.

[0068] By virtue of the extension that, instead of the charging voltage U.sub.L of an individual battery cell, the maximum of the charging voltages U.sub.L of all the present battery cells of a battery pack is initially formed, the method is also directly to a battery pack with a plurality of battery cells.

[0069] It goes without saying that the present invention is not restricted to the exemplary embodiment shown.

[0070] Step S4 can therefore also be executed at another point, for example if the values of ΔU and U.sub.Z or U.sub.Z,n are already known, and it is therefore also known how many discharge pulses P1 to P9 can be generated. In this case, step S5 can be executed immediately after step S3 and from step S6 there can be a branch back to step S5 via step S7 until the last discharge pulse P9 has been applied. Analogously to step S4, a check is subsequently carried out to determine whether the charging voltage U.sub.L has reached the changeover voltage U.sub.U. In particular, a check can then be carried out in step S7 to determine whether the known last value for n (“nfinal”, in the present exemplary embodiment, for example, nfinal=9) has been reached and there can then be a branch to step S4.

[0071] In general, “a(n)”, “one”, etc. can be understood as a singular or a plural, particularly in the sense of “at least one” or “one or more”, etc., as long as this is not explicitly excluded, e.g. by the expression “exactly one”, etc.

[0072] A numerical value can also comprise precisely the specified number and a customary tolerance range, as long as this is not explicitly ruled out.

LIST OF REFERENCE SIGNS

[0073] BV Battery charging apparatus [0074] C Value of the C factor [0075] F Vehicle [0076] I.sub.SE Discharge current [0077] I.sub.L Charging current [0078] LP1-LP3 Charging phase [0079] LSt Charging station [0080] n Index of a further discharge pulse [0081] P0 First discharge pulse [0082] P1-P9 Further discharge pulse [0083] S1-S7 Method steps [0084] U.sub.A Anode voltage [0085] U.sub.A,krit Critical anode voltage [0086] U.sub.L Charging voltage [0087] U.sub.SE Trigger voltage [0088] U.sub.U Changeover voltage [0089] U.sub.Z Additional voltage value [0090] U.sub.Z,n Additional voltage value of the nth further discharge pulse [0091] t.sub.SE Trigger time [0092] t1 Changeover time [0093] t2 Changeover time [0094] ΔU Difference