Patent ID: 12255486

DETAILED DESCRIPTION OF THE DRAWINGS

FIG.1shows 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 ILin amperes for a plurality of charging phases LP1, LP2and LP3in an upper plot, the charging voltage UL, applied to the same battery cell, in volts, in a middle plot, and the associated anode voltage UAin volts in a lower plot.

With respect to the upper plot, the charging phases LP1, LP2, LP3have a charging current ILthat in each case is constant but gradually decreasing for successive charging phases LP1, LP2, LP3, for example IL=125 A during LP1, IL=90 A during LP2and IL=75 A during LP3, etc. The changeover time between LP1and LP2is referred to as t1and the changeover time between LP2and LP3is referred to as t2. At the changeover times t1and t2, the associated charging current ILis decreased in a stepped manner.

The middle plot shows that the charging voltage UL, which is needed for maintaining a constant charging current IL, typically increases continuously for a respective charging phase LP1to LP3after initially decreasing for a short time following a changeover between two charging phases LP1, LP2or LP2, LP3. The changeover is triggered or carried out when the charging voltage ULof a charging phase LP1to LP3reaches a respective changeover voltage UU. The changeover voltages UUcan 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 ULof a following charging phase LP2, LP3exceeds the changeover voltage UUof the preceding charging phase LP1or LP2comparatively quickly. By way of example, it may be the case that UU(LP1)=3.95 V, UU(LP2)=4.00 V and UU(LP3)=4.05 V.

The lower plot shows that the anode voltage UAmeasured overall against Li/Li+, for example, decreases during each of the charging phases LP1to LP3. If the anode voltage UAwere to become negative in the course of the charging phase LP1, LP2, LP3, plating would occur. The overall anode voltage UAis 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 UAcan arise, wherein a negative anode voltage can occur locally even if the overall measured anode voltage UAis 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 UA,kritis reached or fallen below.

This critical anode voltage UA,kritis reached at a time tSE, and a trigger voltage USEfor triggering or initiating at least the first discharge pulse P0, in particular the discharge pulses P0to P9(seeFIG.3), is advantageously set in such a way that the charging voltage ULlikewise reaches this trigger voltage USEat least approximately at the time tSE. In other words, the trigger voltage USEis selected such that it coincides with the critical anode voltage UA,kritbeing reached. This means that discharge pulses P0to P9preventing plating are injected or applied only when it is necessary, specifically if the anode voltage UAenters the voltage range UA≤UA,kritthat is critical for the plating. The application of discharge pulses P0to P9that increase the charging time of the battery cell to time or voltage ranges t<tSEor UA>UA,kritthat 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 LP1to LP3is advantageously delayed for as long as possible, which also means that the anode voltage UAshould be brought as close as possible to UA=0. This objective can be largely achieved, without producing plating, through the use of the discharge pulses P0to P9, also taking inhomogeneities, shape, etc. of the anode into consideration.

FIG.2shows 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.3shows a corresponding plot of the current I, flowing to and from the battery cell, against time t for the first charging phase LP1.

In a step S1, a charging phase LP1is started at the beginning of a charging operation, for example.

Then, monitoring is carried out in step S2to determine whether the difference ΔU between the changeover voltage UUand the applied charging voltage ULis reached or fallen below, or whether the charging voltage ULhas reached or exceeded the trigger voltage USE=UU−ΔU.

If this is the case (“Y”), in a step S3, a first discharge pulse P0of, for example, a duration between 0.1 s and 10 s is injected, as also shown inFIG.3.

Following the end of the first discharge pulse P0, monitoring is carried out in step S4to determine whether the charging voltage ULhas reached the changeover voltage UU. If this is the case (“Y”), there is a changeover to a following charging phase LP1, LP2, LP3or a new charging phase LP1, LP2, LP3is begun.

If this is not the case (“N”), monitoring is carried out in step S5to determine whether the charging voltage ULhas reached the trigger voltage USEplus an nth additional voltage value UZ,n, wherein n is the number of the additional (second, etc.) discharge pulses P1to P9. Monitoring is therefore carried out to determine whether UL≥USE+UZ,n. If the discharge pulses P1to P9are intended to be triggered equidistantly with respect to the voltage, the trigger condition can also be described as UL≥USE+n·UZ, wherein n=1 for the first additional discharge pulse.

If this is the case (“Y”), a further nth discharge pulse P1to P9is applied in step S6and, following the end of this, in step S7there is a branch back to step S4, with n being incremented (n≈n+1). In the present case, nine further discharge pulses P1to P9are applied, for example.

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

As shown inFIG.3, the discharge pulses P1to P9can 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−1, a discharge current ISEis advantageously set to ISE≤−C/10, in this case particularly advantageously to ISE=−C amperes. By way of example, the discharge current can be ISE=−60 A. In particular, the amount of charge that is discharged by injecting the discharge pulses P0to P9collectively during the associated charging phase LP1is at least 0.1% of the amount of charge of the associated charging phase LP1and/or does not exceed 2% of the amount of charge.

For example, it may be the case that ΔU=10 mV, while, for example, it may be the case that UZ=1 mV.

By virtue of the extension that, instead of the charging voltage ULof an individual battery cell, the maximum of the charging voltages ULof 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.

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

Step S4can therefore also be executed at another point, for example if the values of ΔU and UZor UZ,nare already known, and it is therefore also known how many discharge pulses P1to P9can be generated. In this case, step S5can be executed immediately after step S3and from step S6there can be a branch back to step S5via step S7until the last discharge pulse P9has been applied. Analogously to step S4, a check is subsequently carried out to determine whether the charging voltage ULhas reached the changeover voltage UU. In particular, a check can then be carried out in step S7to 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.

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.

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

BV Battery charging apparatusC Value of the C factorF VehicleISEDischarge currentILCharging currentLP1-LP3Charging phaseLSt Charging stationn Index of a further discharge pulseP0First discharge pulseP1-P9Further discharge pulseS1-S7Method stepsUAAnode voltageUA,kritCritical anode voltageULCharging voltageUSETrigger voltageUUChangeover voltageUZAdditional voltage valueUZ,nAdditional voltage value of the nth further discharge pulsetSETrigger timet1Changeover timet2Changeover timeΔU Difference