Charging of battery cells

Abstract

The invention relates to a method for charging a battery cell, which is monitored during a charging phase (LP1-LP2) with a constant charging current (I L ), whether the charging voltage (U L ) applied to the battery cell reaches or exceeds a preset switching voltage (U U ), and if this is the case, it is switched to the next charging phase (LP2-LP3) with a smaller constant charging current (I L ), and additionally monitored during each charging phase (LP1-LP3) whether a preset gap (ΔU) between the charging voltage (U L ) and the switching voltage (U U ) of the charging phase (LP1-LP3) is reached or undershot, and if so, at least one discharge pulse (P0-P9) is applied to the battery cell. A battery charging device (BV) is set up to carry out the method. A vehicle (F) and / or a charging station (LSt) has at least part of the battery charging device (BV). The invention can be advantageously applied in particular to the charging of vehicle batteries, especially to the charging of vehicles electrically driven by batteries.

Description

Technical Field

[0001] The invention relates to a method for charging a battery cell, wherein during a charging phase with an at least approximately constant charging current it is monitored whether the charging voltage applied to the battery cell reaches or exceeds a preset switching voltage and, if this is the case, a switch is made to the next charging phase with an at least approximately constant but lower charging current. The invention also relates to a battery charging device, which is configured to carry out the method. The invention also relates to a vehicle having at least a part of a battery charging device and / or to a charging station for a vehicle having at least a part of a battery charging device. The invention can be applied in particular advantageously to the charging of vehicle batteries, in particular to the charging of battery-electrically driven vehicles. Background Art

[0002] Fast charging is a very important factor for the user acceptance of battery electric vehicles. Here, the goal is to be able to achieve particularly short charging times without compromising the safety or service life of the storage device.

[0003] In the case of multi-stage constant current charging (also called "multi-stage constant current", MSCC), the charging current is gradually reduced in steps so that the anode potential of the charged battery cell does not change to the following range, in which the deposition of metallic lithium on the electrode of the battery cell (so-called "plating") occurs. This results in a characteristic step pattern for the charging current, which is described, for example, in US Pat. No. 6,137,265 A. Figure 3 B and has been used to charge current battery electric vehicles.

[0004] In MSCC, despite the fact that an anodic potential is determined as a whole or over the entire anode at which plating should not be allowed, plating may still occur, since the current and current density at and in the actual electrode are inhomogeneous, for example due to the interaction of transport processes with inhomogeneities in the electrode structure, the porous structure of the electrode and the limited extension of the electrode. The global anodic potential is therefore a mixture of different local anodic potentials, where the local anodic potentials can have values ​​at which plating occurs, even though this should not occur when only the global anodic potential is considered. In order to counteract plating under real conditions, the charging current can be reduced, which, however, disadvantageously leads to a prolonged charging time. Summary of the invention

[0005] The object of the present invention is to at least partially overcome the disadvantages of the prior art and in particular to provide a multi-stage constant current charging which particularly reliably prevents electroplating with only a slight increase in the charging time.

[0006] This object is achieved according to the features of the invention.

[0007] This object is achieved by a method for charging a battery cell, wherein:

[0008] - during a charging phase with an at least approximately constant charging current or with a charging current having an at least approximately constant current intensity, monitoring whether the charging voltage applied to the battery cell reaches or exceeds a predefined switching voltage, and if this is the case, switching to a next charging phase with a lower at least approximately constant charging current or with a charging current having a lower, likewise at least approximately constant current intensity, and

[0009] During the charging phase, it is additionally monitored whether the charging voltage reaches or falls below a predefined difference from the switching voltage of this charging phase and, if so, at least one discharge pulse is applied to the battery cell.

[0010] The method is implemented by applying at least one discharge pulse, thereby preventing deposits on the electrodes of the battery cells, for example, deposits of metallic lithium on the anodes of lithium-ion battery cells, and even decomposing existing deposits if necessary. In addition, since the at least one discharge pulse is applied or applied at a relatively late time point in the corresponding charging phase, the risk of electroplating is particularly high at this time point, so the discharge pulse plays a particularly effective role. As a result, only relatively few and short discharge pulses are required, which in turn only slightly prolongs the charging time. In other words, the discharge pulse is not triggered at a pre-fixed preset time point (for example, periodically), but is triggered only when the risk of electroplating is particularly high. In particular, the preset gap corresponds to the anode voltage, which has been so close to its zero value in the course of the charging phase that there is a significantly increased risk of electroplating due to the inhomogeneity of the electrodes, especially the anode, for example because a negative anode potential may have been applied locally there, although the overall anode potential is still positive.

[0011] The current intensity being "at least approximately" constant during the charging phase includes, in particular, that the current intensity deviates, in particular decreases, from its initial value or initial setpoint value during the charging phase by no more than 10%. In a further development, this means that the current intensity deviates, in particular decreases, from the initial current intensity by no more than 5%, in particular by no more than 4%, in particular by no more than 3%, in particular by no more than 2%, in particular by no more than 1%.

[0012] In one refinement, the current intensity deviates from its initial value or initial rated value during a charging phase by a significantly smaller value than the initial value or initial rated value of two consecutive charging phases, in particular by at least one order of magnitude. In one refinement, the deviation within a charging phase is no more than 10%, in particular no more than 5%, in particular no more than 4%, in particular no more than 3%, in particular no more than 2%, in particular no more than 1%, of the difference between the initial value or initial rated value of the charging phase and the initial value or initial rated value of the preceding charging phase and / or the following charging phase.

[0013] One development is that the charging power is kept constant during the charging phase. Since the charging voltage increases slightly during charging of the battery cells with a constant charging current, in this development, instead of keeping the charging current constant, the current intensity of the charging current is reduced (slightly) in a targeted manner to such an extent that the charging voltage increases. This can be achieved by keeping the charging power constant during the charging phase. However, this drop in the charging current is significantly smaller than the drop during the switchover at the end of the charging phase.

[0014] One embodiment is to apply a constant charging current or a charging current with a constant current intensity during the charging phase and to switch to the next charging phase with a smaller constant charging current or a charging current with a smaller constant current intensity when the charging voltage applied to the battery cell reaches or exceeds a preset switching voltage. This embodiment is an MSCC method in a narrow sense, wherein during the execution of the MSCC method, a plurality of successive charging phases are set or exist, which have a gradually decreasing charging current, but each (except for the discharge pulses) is constant.

[0015] The case of a constant charging current and a constant charging power can therefore be considered as an alternative embodiment of the superordinate inventive concept. In this context, a constant charging current or a constant charging power can be understood to mean that they are set or adjusted to a corresponding constant rated value during the charging phase. The deviation from the rated value during the charging phase is advantageously less than 2%, in particular less than 1%, in particular less than 0.5%.

[0016] In the present method, in a modified scheme, the transition occurs directly between successive charging phases, that is, there is no obvious and targeted transition phase. In other words, during the charging process, in particular, a staged reduction of the charging current is carried out. The corresponding charging voltage applied to the battery cell and can be simply measured rises continuously after a short drop at the beginning of the charging phase. Typically, when the charging voltage reaches or exceeds a preset switching voltage, a transition is made from one charging phase to the next charging phase. The switching voltage typically corresponds at least approximately to the anode voltage approaching its zero value, typically to reaching a preset threshold value (also called "critical anode voltage") of about 10mV to 40mV above the zero value, thereby achieving the advantage of compensating for inhomogeneities and model errors of the simulation. The switching voltage can be different from charging phase to charging phase and usually increases with the charging phase that continues. In other words, in order to determine the desired switching time point between two charging phases, it is monitored whether the charging voltage applied to the battery cell reaches or exceeds the preset switching voltage, and if this is the case, the next charging phase is switched.

[0017] The invention is described in more detail below with reference to a constant charging current for the respective charging phases. However, the invention similarly includes charging phases with a charging current that is also only at least approximately constant, for example charging phases with a constant charging power during which the charging current only drops slightly.

[0018] A "battery cell" is understood to be a single battery cell in particular. A plurality of battery cells can be combined to form a "battery pack" or a "battery storage unit". In this case, the electrical connection of the battery cells is in principle arbitrary, for example in series and / or in parallel. A development is that the voltages applied to all battery cells of the battery pack, including the charging voltage, can be monitored individually or separately. Alternatively or additionally, the voltage applied to the battery pack as a whole can be measured. In addition, the corresponding current can also be measured, that is, the corresponding current can be measured individually and / or collectively.

[0019] The difference is in particular equal to the difference between the current charging voltage and the switching voltage. During the charging phase, additional monitoring of whether the difference reaches or falls below a first threshold value can also be implemented in a similar manner by additionally monitoring whether the charging voltage has reached or exceeded a voltage value ("trigger voltage") which is equal to the first threshold value minus the difference. Calculation methods and other equivalent definitions can be used interchangeably.

[0020] The discharge pulse discharges the battery cell during its duration. In the following, without limiting the generality, the charging current is provided with a positive sign and the discharging current is provided with a negative sign. The battery voltage during discharge is less than its equilibrium potential at the current point in time. This voltage difference relative to the equilibrium potential has a sign change when changing between charging and discharging.

[0021] The method continues until a predefined interruption criterion is reached, for example, a battery cell has reached a sufficient charge level or a certain total charging time has been reached.

[0022] It may happen that the charging voltage drops again to less than the trigger voltage set for triggering the discharge pulse after the discharge pulse ends and then reaches or exceeds the trigger voltage again. In this case, it is advantageous to no longer apply a discharge pulse to the same trigger voltage. In general, one improvement is that during the charging phase, when a preset trigger voltage is reached or exceeded multiple times or when a preset difference is reached or fallen below multiple times (i.e., especially when it is reached, exceeded or fallen below for the first time), the associated discharge pulse is triggered only once.

[0023] In one configuration, the duration of the at least one discharge pulse is in a range between 0.1 s and 10 s, in particular in a range between 0.5 s and 2 s, in particular approximately 1 s.

[0024] In one embodiment, the discharge pulse has an amplitude which is not less than a value C / 10, in particular not less than a value C / 3, in particular not less than a value C / 2, of the C rate of the battery cell. The C rate or C factor is a known battery-specific parameter which will not be discussed further here. If this parameter is C [h -1 ], the discharge pulse is advantageously set so that the discharge pulse has a discharge current I of at least -C / 10 amperes SE The current intensity or the magnitude of C / 10 amperes |I SE |. It is therefore applicable that I SE ≤-C / 10 or |I SE | > C / 10. The discharge current I of the discharge pulse is set by a (unitless) value based on the C-rate of the battery cell with a preset relationship SE The strength of the discharge pulse ensures a favorable selection regardless of the capacity of the monomer.

[0025] One development is that the amplitude of the discharge pulse does not exceed a value of 1 C. Limiting the C rate to a maximum value of 1 C has the advantage, on the one hand, of limiting the circuit technology expenditure, and, on the other hand, at very high C rates and a constant charge, the pulses are applied only for a correspondingly short time, so that decomposition or other homogenization processes of any deposited or plated lithium cannot take place in the electrode or cannot take place for a sufficiently long time. However, in principle, it is also possible to select a value greater than 1 C for the amplitude of the discharge pulse value, for example 2 C, 5 C, 10 C, etc.

[0026] Generally, one design is that the charge discharged in the case of a discharge pulse ("discharge pulse charge") increases as the health of the battery cell decreases. The advantage achieved thereby is that it is also taken into account that the tendency to electroplating in aged battery cells may be higher than in healthy battery cells. The increased discharge pulse charge serves as a counteraction to the reduced health. The health can be quantified by a so-called SoH characteristic value ("state of health", SoH), which gives information about what percentage of the initial battery cell capacity can still be used in the current charging cycle. A healthy battery cell corresponds to an SoH of 1 or 100%. Therefore, the design can be expressed as follows: the charge discharged in the case of a discharge pulse ("discharge pulse charge") increases as the SoH value of the battery cell decreases. A particularly advantageous improvement is that the amplitude of the discharge pulse increases inversely proportional to the SoH characteristic value.

[0027] In one embodiment, the discharge pulse of a healthy battery cell has an amplitude which does not exceed a value C of the C rate of the battery cell, in particular is equal to the value C, and which increases as the health level decreases.

[0028] An alternative improvement is that the C rate of the discharge pulse remains constant with a decrease in the SoH characteristic value, which corresponds to a decrease in the current amplitude in the case of a decrease in the SOH value. However, as a further possibility, the C rate of the discharge pulse can be kept constant. Furthermore, alternatively or additionally, the discharge pulse duration can be increased with a decrease in the SOH value.

[0029] In one embodiment, the discharge quantity (for example given in coulombs) accumulated on the battery cell during a specific charging phase by the at least one discharge pulse does not exceed 5%, in particular not exceed 4%, in particular not exceed 3%, in particular not exceed 2%, in particular not exceed 1% of the charge quantity of this charging phase. This is because it has been shown that even with such a small discharge quantity, electroplating can be prevented in an improved manner and the extension of the charging time can be kept short.

[0030] An improvement is that the discharge amount is at least 0.1%, in particular at least 0.2%, and in particular at least 0.5% of the charge amount in the charging stage. Thus, electroplating is effectively prevented.

[0031] It is particularly advantageous if the discharge amount is between 0.1% and 1% of the charge amount.

[0032] One design is to apply multiple discharge pulses to the battery cells at intervals during the charging phase to reach the preset gap or the associated trigger voltage. This has the advantage that the effect of the discharge pulses on suppressing or reversing electroplating is distributed over a longer period of time, which makes the anti-electroplating effect particularly effective.

[0033] One development consists in that the discharge pulses are applied or administered in a fixed predetermined time sequence.

[0034] One design solution is that, following the first discharge pulse, a further or additional discharge pulse is always applied if the charging voltage has increased by a preset value (“additional voltage value”) since the gap was reached. Thus, the discharge pulse is applied at a time point that is particularly advantageous for preventing electroplating. For example, for a certain charging phase, the switching voltage can be U U And the trigger voltage U for applying the first discharge pulse SE With switching voltage U U The difference ΔU means that U SE = U U -ΔU applies, where the voltage U SE , U U , ΔU has a positive sign, so U SE < U U Applicable. When the voltage applied to the battery cell (charging voltage) U L = U SE When applicable, the first discharge pulse P0 is triggered, when the charging voltage U L = U SE + n·U Z (Wherein, the preset additional voltage value U Z >0), triggers every nth additional discharge pulse Pn of this charging phase. Z , especially U Z ≤ΔU / 2 applies. The natural positive number n therefore specifies the number of further or additional discharge pulses P1 to P9 following the first discharge pulse P0 of this charging phase.

[0035] An improved solution is to add a voltage value U Z has the same value for all discharge pulses. Alternatively, the additional voltage value U Z The discharge pulses may be different for at least two of the discharge pulses.

[0036] One design solution is that the gap or its value or size is at least approximately equal to a critical threshold of the anode voltage of the battery cell. As the critical threshold is reached or dropped below, the risk of electroplating increases significantly. For example, the "critical anode voltage" can be estimated or determined by experiment or by simulation. For example, the critical anode voltage can have a value between about 10 mV and 40 mV.

[0037] In one embodiment, the size of the difference is constant for all charging phases.

[0038] An alternative design is that the size of the difference is different for at least two charging phases. Therefore, the size of the difference can become larger or smaller with the subsequent charging phase.

[0039] Generally, the at least one discharge pulse need not be applied in all charging phases, but only in the first n charging phases of a group of m>n charging phases. This is advantageous when the risk of electroplating in charging phases greater than n is practically excluded.

[0040] One development is that the size of the gap is varied for the respective charging phase, for example as a function of the SoH characteristic value (“state of health”, SoH) of the battery cell. In particular, the gap can increase as the SoH characteristic value decreases. This also achieves the advantage that the health state of the battery cell is taken into account to prevent electroplating.

[0041] One design solution is to charge a lithium-based battery cell, such as a lithium-ion battery cell, a lithium-polymer battery cell, or a lithium-containing solid battery cell, or the lithium-containing battery cell is a lithium-based battery cell.

[0042] One design is to connect a plurality of battery cells in combination to form a battery pack or battery storage. The method can then be performed in a similar manner. This can be achieved particularly easily if the charging voltages of the individual battery cells of the battery pack can be measured individually and can be set individually.

[0043] In one embodiment, reaching or falling below this gap is monitored individually for each battery cell of the battery and at least one discharge pulse is applied to the battery even if only one battery cell reaches or falls below this gap. This method offers the advantage that electroplating can be particularly reliably prevented even when the charging voltage of the individual battery cells of the battery can be measured individually, but the charging voltage is applied to the battery as a whole. In particular, in this embodiment, the following can be performed: the battery is charged, wherein a first charging phase is first carried out. Now one of the battery cells first reaches the trigger voltage U SE . A discharge pulse is then applied to the entire battery pack. Subsequently, the battery pack is charged further (here, the trigger voltage USE can be passed again, but for the trigger voltage U SE No new discharge pulse is performed, because the trigger voltage has already been triggered once), and the battery cell (possibly having first reached the trigger voltage U SE The same battery cell) will reach the switching voltage U U This forces a change to the next charging phase with a consequent abrupt reduction in the charging current.

[0044] In a particularly simply constructed battery pack, in which the individual battery cells are connected in series and the charging voltage of the individual battery cells cannot be measured individually, the method can be carried out in a similar manner, for example, as follows: for m battery cells, for the charging voltage U L Applicable U L = U L,pack / m, where U L = U L,pack is the charging voltage applied to the battery pack.

[0045] The object is also achieved by a battery charger, wherein the battery charger is configured to carry out the method described above. The battery charger can be designed similarly to the method and have the same advantages. The battery charger can have, for example, supply terminals for providing electrical energy, a measuring device for measuring the voltage applied to a battery cell or a battery pack, a current measuring device for measuring the current flowing to and / or out of the battery cell or battery pack, if necessary, and a control device for controlling the method.

[0046] The object is also achieved by a vehicle having at least a part of a battery charging device. The battery charging device can be constructed similarly to the battery charging device and / or the method and has the same advantages. In a further development, the vehicle is a battery-electrically driven vehicle. The vehicle can be, for example, a motor vehicle (for example a car such as a car, a truck, a bus, etc., or a motorcycle), a train, a water vehicle (for example a ship or a boat) or an air vehicle (for example an airplane or a helicopter).

[0047] Furthermore, the object is achieved by a charging station for a vehicle, which has at least a part of a battery charging device.

[0048] Therefore, the battery charging device can be implemented in the vehicle, the charging station, or can be implemented in a distributed manner on the vehicle and the matching charging station.

[0049] The above-described characteristics, features and advantages of the present invention as well as ways and methods for achieving these characteristics, features and advantages become clearer and more clearly understandable in conjunction with the following schematic description of an embodiment, which is explained in more detail in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Three diagrams showing charging parameters versus time in minutes describing a charging process of the MSCC, diagrammatically and not to scale, without a discharge pulse as yet;

[0051] Figure 2 shows a possible flow chart for carrying out the method; and

[0052] Figure 3 The diagram shows diagrammatically and not to scale the current flowing to and from the battery cell during the charging phase with a discharge pulse after the associated trigger voltage has been reached. DETAILED DESCRIPTION

[0053] Figure 1 Graphs showing typical charging parameters of an MSCC charging process for a lithium-ion battery cell without a discharge pulse versus time t in minutes, i.e. the upper graph shows the charging current I in amperes for a plurality of charging phases LP1, LP2 and LP3 L , the middle diagram shows the charging voltage U in volts applied to the same battery cell. L , and the associated anode voltage U in volts is shown in the following diagram. A .

[0054] With regard to the above diagram, each charging phase LP1, LP2, LP3 has a charging current I which is constant but gradually decreases for successive charging phases LP1, LP2, LP3. L , for example, during LP1 I L =125 A, during LP2 I L =90A, and during LP3 I L =75A, etc. The switching time between LP1 and LP2 is denoted as t1, and the switching time between LP2 and LP3 is denoted as t2. At the switching time t1 and t2, the corresponding charging current I L Step down.

[0055] The middle diagram shows that for the respective charging phases LP1 to LP3, a constant charging current I L Required charging voltage U LTypically, the charging voltage rises continuously, and then drops for a short time after switching between two charging phases LP1, LP2 or between LP2, LP3. L Reach the corresponding switching voltage U U When the switching voltage U U In particular, it can be selected such that the switching voltage is larger for each subsequent charging phase LP1, LP2, LP3. This is usually sensible, since the charging voltage U of the subsequent charging phase LP2, LP3 is L Relatively quickly exceeds the switching voltage U of the previous charging phase LP1 or LP2 U For example, it can be applied that: U (LP1) = 3.95V, U U (LP2) = 4.00V and U U (LP3) = 4.05V.

[0056] The following diagram shows, for example, for Li / Li + The overall measured anode voltage U A During each of the charging phases LP1 to LP3, the anode voltage U A If the voltage U is negative during the charging phases LP1, LP2, and LP3, electroplating will occur. A During the charging process, it remains at a positive value. However, due to the inhomogeneity, shape, etc. of the anode, deviations from the overall measured anode voltage U A local deviations, whereby even if the overall measured anode voltage U A Still positive, it is also possible that a negative anode voltage has already occurred locally. Therefore, for this method it is assumed that as the positive critical anode voltage U is reached or falls below A,krit , the risk of local electroplating has increased significantly.

[0057] At time point t SE When the critical anode voltage U A,krit , and is used to trigger or start at least a first discharge pulse P0, in particular discharge pulses P0 to P9 (see Figure 3 ) trigger voltage U SE is advantageously determined so that the charging voltage U L Likewise, at least approximately at time t SE When the trigger voltage U SE In other words, the trigger voltage U SE is selected to reach the critical anode voltage U A,krit This allows, when necessary, that is, as the anode voltage U AAppears in the critical voltage range U for electroplating A ≤U A,krit The discharge pulses P0 to P9 that prevent electroplating are applied or applied only when the electroplating is not critical. <t SE Or voltage range U A >U A,krit Discharge pulses P0 to P9 are applied to extend the charging time of the battery cells. It is also considered that in order to achieve a short charging time, it is advantageous to delay the switching of the charging phases LP1 to LP3 as long as possible, which also means that the anode voltage U A As close as possible to U A = 0. By using discharge pulses P0 to P9, this purpose can be achieved to a large extent without causing electroplating, even taking into account the non-uniformity, shape, etc. of the anode.

[0058] Figure 2 A possible flow chart for carrying out the method in a battery charging device BV is shown. The battery charging device BV may represent a part or a component of a vehicle F and / or a charging station LSt. Figure 3 A corresponding diagram shows the current I flowing into and out of the battery cell over the time t for the first charging phase LP1 .

[0059] In step S1 , a charging phase LP1 begins, for example at the beginning of a charging process.

[0060] Then, in step S2, it is monitored whether the switching voltage U U and the applied charging voltage U L The difference ΔU between them, or the charging voltage U L Whether the trigger voltage U is reached or exceeded SE =U U -ΔU.

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

[0062] After the first discharge pulse P0 has ended, the charging voltage U L Has the switching voltage U been reached? U If this is the case (“yes”), a switch is made to the following charging phase LP1 , LP2 , LP3 or a new charging phase LP1 , LP2 , LP3 is started.

[0063] If this is not the case (“No”), then in step S5 the charging voltage U LHas the trigger voltage U been reached? SE Add the nth additional voltage value U Z,n , where n is the number of additional (second, etc.) discharge pulses P1 to P9. L ≥U SE +U Z,n If the discharge pulses P1 to P9 are to be triggered equidistantly with respect to voltage, the triggering condition can also be described as U L ≥U SE +n·U Z , wherein for the first additional discharge pulse n=1 applies.

[0064] If this is the case (“yes”), in step S6 a further n-th discharge pulse P1 to P9 is applied and after its completion in step S7 a branch is taken back to step S4 with incrementing n (n:=n+1). In the present example, nine further discharge pulses P1 to P9 are applied.

[0065] This process is performed until the charging process is interrupted or ended. Figure 3 As shown in , the discharge pulses P1 to P9 may have the same pulse duration, for example 1 s, and / or may have the same discharge current amplitude, for example equal to the value of the C rate of the battery cell. If the intrinsic C rate of the battery cell is C h -1 , then the discharge current I SE Advantageously set to I SE ≤-C / 10, here it is particularly advantageous to set it to I SE = -C amperes. For example, it is possible that the discharge current I SE = −60 A. In particular, the charge amount discharged in total during the associated charging phase LP1 by applying the discharge pulses P0 to P9 is at least 0.1% and / or does not exceed 2% of the charge amount of the associated charging phase LP1 .

[0066] For example, it is possible that ΔU=10 mV, and for example U Z =1 mV is applicable.

[0067] By extension, that is, replacing the charging voltage U of a single battery cell L , firstly the charging voltage U of all current battery cells of the battery is formed L The method also directly relates to battery packs having a plurality of battery cells.

[0068] Of course, the invention is not limited to the embodiments shown.

[0069] Therefore, step S4 can also be implemented at other positions, for example, if ΔU and U are known in advance.Z or U Z,n The value of and therefore also know how many discharge pulses P1 to P9 can be generated. In this case, step S5 can be implemented immediately after step S3, and from step S6 through step S7 to step S5, until the last discharge pulse P9 is applied. Then, similar to step S4, the charging voltage U is checked. L Has the switching voltage U been reached? U In particular, it is possible to check in step S7 whether a known final value for n (“nfinal”, in the present exemplary embodiment, for example nfinal=9) has been reached and then branch to step S4 .

[0070] Generally, “a”, “an” etc. can be understood as singular or plural, especially in the sense of “at least one” or “one or more” etc., unless explicitly excluded, for example by the expression “exactly one” etc.

[0071] Quantity specifications may also include exactly the stated quantity and the customary tolerance range, unless this is explicitly excluded.

[0072] Reference numerals list

[0073] BV Battery Charging Unit

[0074] The value of CC factor

[0075] F Vehicle

[0076] I SE Discharge current

[0077] I L Charging Current

[0078] LP1-LP3 charging stage

[0079] LSt Charging Station

[0080] n Additional discharge pulse footer

[0081] P0 First discharge pulse

[0082] P1-P9 Additional discharge pulses

[0083] S1-S7 Method Steps

[0084] U A Anode voltage

[0085] U A,krit Critical anode voltage

[0086] U L Charging voltage

[0087] U SE Trigger voltage

[0088] U U Switching voltage

[0089] U Z Additional voltage value

[0090] U Z,n Additional voltage value of the nth additional discharge pulse

[0091] t SE Trigger time point

[0092] t1 Switching time point

[0093] t2 Switching time point

[0094] ΔU gap.

Claims

1. A method (S1-S7) for charging a battery cell, wherein: - during a charging phase (LP1-LP2) with a first charging current, monitoring (S4) the charging voltage (U L ) reaches or exceeds the preset switching voltage (U U ), the first charging current deviates from its initial value during this charging phase (LP1-LP2) by no more than 10%, and, if this is the case, switching to a next charging phase (LP2-LP3) with a smaller second charging current, the second charging current deviating from its initial value during this charging phase (LP2-LP3) by no more than 10%; and - During the individual charging phases (LP1-LP3), it is additionally monitored (S2) whether the charging voltage (U L ) and the switching voltage (U U ) of a preset difference (ΔU), and if so, applying at least one discharge pulse (P0-P9) to the battery cell (S3-S7).

2. The method (S1-S7) according to claim 1, wherein: The duration of the at least one discharge pulse ( P0 - P9 ) is in each case in the range between 0.1 s and 10 s.

3. The method (S1-S7) according to claim 1, wherein: The duration of the at least one discharge pulse ( P0 - P9 ) is in each case in the range between 0.5 s and 2 s.

4. The method (S1-S7) according to claim 1, wherein: The duration of the at least one discharge pulse (P0-P9) is in each case 1 s.

5. The method (S1-S7) according to any one of claims 1 to 4, wherein: The at least one discharge pulse (P0-P9) has an amplitude which is not lower than a value C / 10 of the C-rate (C) of the battery cell.

6. The method (S1-S7) according to any one of claims 1 to 4, wherein: The discharge amount accumulated to the battery cell by the at least one discharge pulse (P0-P9) during the charging phase (LP1-LP3) does not exceed 5% of the charge amount in the charging phase (LP1-LP3).

7. The method (S1-S7) according to any one of claims 1 to 4, wherein: The discharge amount accumulated to the battery cell by the at least one discharge pulse (P0-P9) during the charging phase (LP1-LP3) does not exceed 1% of the charge amount in the charging phase (LP1-LP3).

8. The method (S1-S7) according to any one of claims 1 to 4, wherein: The discharge amount accumulated to the battery cell by the at least one discharge pulse (P0-P9) during the charging phase (LP1-LP3) is between 0.1% and 1% of the charge amount in the charging phase (LP1-LP3).

9. The method (S1-S7) according to any one of claims 1 to 4, wherein: During a charging phase (LP1-LP3), as the gap (ΔU) is reached or fallen below, a plurality of discharge pulses (P0-P9) are applied to the battery cell at intervals in time (S5-S7).

10. The method (S1-S7) according to claim 9, wherein: Following the first discharge pulse (P0), if the charging voltage (U L ) has been increased by a predetermined additional voltage value (U Z , U Z,n ), then additional discharge pulses (P1-P9) are always applied (S5-S7).

11. The method (S1-S7) according to any one of claims 1 to 4, wherein: The difference (ΔU) is equal to the anode voltage (U A ) of the critical threshold (U A,krit ).

12. The method (S1-S7) according to any one of claims 1 to 4, wherein: The difference (ΔU) is constant for all charging phases ( LP1 - LP3 ).

13. The method (S1-S7) according to any one of claims 1 to 4, wherein: The difference (ΔU) is different for at least two charging phases ( LP1 - LP3 ).

14. The method (S1-S7) according to any one of claims 1 to 4, wherein: Charge the lithium-based battery cells.

15. The method (S1-S7) according to any one of claims 1 to 4, wherein: Charge the lithium battery cells.

16. The method according to any one of claims 1 to 4, wherein: Connect multiple battery cells into a battery pack.

17. The method according to claim 16, wherein: Reaching or falling below the difference (ΔU) is monitored individually for each cell of the battery pack, and at least one discharge pulse (P0-P9) is applied to the battery pack even if only one cell reaches or falls below the difference (ΔU).

18. A battery charging device (BV), wherein: The battery charging device is configured to perform a method (S1-S7) according to any one of claims 1 to 17.

19. A vehicle (F) comprising at least a portion of a battery charging device (BV) according to claim 18.

20. A charging station (LSt) for a vehicle (F), comprising at least a portion of a battery charging device (BV) according to claim 18.

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