Patent Application
20240348076
The present invention relates to a battery cell charging method for charging a lithium ion battery cell of a battery pack of an electric hand-held power tool. In the battery cell charging method, a charging current made available to the lithium ion battery cell is set on the basis of a cell state characterizing the lithium ion battery cell. Battery cell charging methods which are controlled on the basis of a temperature cell state of the lithium ion battery cell of a battery pack are fundamentally known from the prior art.
EP 2 276 139 B1 describes a battery cell charging method for charging a lithium ion battery cell, wherein the battery cell charging method comprises applying a variable charging voltage and a variable current to the battery cell on the basis of a continuously variable voltage charging profile, wherein the continuously variable voltage charging profile is determined on the basis of an imaginary resistance which is in series with a resistance of a DC model of the battery cell.
U.S. Pat. No. 8,116,998 B2 discloses a method for determining a state of health of a battery cell in order to determine whether the battery cell is defective.
It is an object of the present invention to specify a battery cell charging method for charging a lithium ion battery cell of an electric hand-held power tool, which method creates the basis for an increased service life of the lithium ion battery pack and the basis for shortening the charging time.
The present invention provides that the cell state characterizing the lithium ion battery cell is a state of health (SoH) and/or an internal resistance (DCR) of the lithium ion battery cell.
The invention includes the knowledge that temperature-based charging of a lithium ion battery pack of an electric hand-held power tool enables only inaccurate charging currents which are not matched to the state of health (SoH) of the lithium ion battery cell. As a result, the charging times for lithium ion battery cells with a good SoH are longer than necessary. In the case of lithium ion battery cells with a poor SoH, aging advances more quickly since the charging currents are possibly too high and damage the lithium ion battery cells.
It has also been recognized that the state of health (SoH) of the lithium ion battery cells can be assumed to be directly proportional to the resistance (DCR) of the lithium ion battery cell. It is therefore possible to adapt the charging current to the respective SoH after the DCR has been determined. Therefore, in the case of a lithium ion battery cell with a good state of health (this corresponds to a comparatively low internal resistance DCR), the charging current can be increased, on the one hand, which shortens the charging times. On the other hand, in the case of an aged lithium ion battery cell (this corresponds to a comparatively high internal resistance DCR), the charging current can be reduced, which slows down aging of the lithium ion battery cell and therefore increases the service life.
In one particularly preferred configuration of the method, the internal resistance of the lithium ion battery cell is measured and/or determined. For this purpose, an open-circuit voltage of the lithium ion battery cell can be measured without a load and/or an operating voltage of the lithium ion battery cell loaded with a predefined resistance.
It has been found to be advantageous if a lower charging current than the preceding charging current is set when a predetermined internal resistance threshold is exceeded. Alternatively or additionally, a higher charging current than the preceding charging current can be set when a predetermined internal resistance threshold is undershot. It has been found to be advantageous if at least two, preferably three, internal resistance thresholds are provided.
In one particularly preferred configuration of the method, the charging current is set in discrete steps, preferably solely in discrete steps. It has been found to be advantageous if at least three, preferably four, discrete and mutually different charging currents are provided. In a further particularly preferred configuration, the internal resistance determined at the end of a respective charging process is stored.
In one particularly preferred configuration of the method, the battery pack may have a plurality of lithium ion battery cells. It has been found to be advantageous if the charging current provided is set on the basis of an averaged internal resistance of the plurality of lithium ion battery cells. It has likewise been found to be advantageous if an open-circuit voltage (DC voltage) of the battery pack is less than 60 volts and is preferably 12 volts, 22 volts or 36 volts.
In a further preferred configuration, provision may be made for the internal resistance of the lithium ion battery cell to be weighted with a temperature cell state of the lithium ion battery cell, in particular before a charging current is determined. The internal resistance can therefore be multiplied by a reciprocal of the cell temperature (or a multiple of the reciprocal), for example. The reciprocal can be discretized. It is conceivable to predefine the charging current by means of a lookup table. In another particularly preferred configuration of the method, a temperature cell state of the lithium ion battery cell is used only for an emergency shutdown of the charging process.
The present invention also provides a battery cell charging system for charging a lithium ion battery cell of a battery pack of an electric hand-held power tool, wherein the battery cell charging system has a charging controller which is configured to set a charging current made available to the lithium ion battery cell on the basis of a cell state characterizing the lithium ion battery cell. The cell state characterizing the lithium ion battery cell is a state of health and/or an internal resistance of the lithium ion battery cell. It has been found to be advantageous if the charging controller is arranged in the battery pack. Alternatively, the charging controller may be included in a charging station of the battery cell charging system. The battery cell charging system can be accordingly developed by means of the features used with respect to the battery cell charging method.
Further advantages will become apparent from the following description of the figures. Particularly preferred exemplary embodiments of the present invention are illustrated in the figures. The figures, the description and the claims contain numerous features in combination. A person skilled in the art will expediently also consider the features individually and combine them to form useful further combinations.
Identical and similar components are denoted by the same reference signs in the figures, in which:
A preferred exemplary embodiment of a battery cell charging method is intended to be explained with reference to the schematic diagrammatic form shown in
Within the scope of the method according to the invention, provision is made for the charging current made available to the lithium ion battery cell to be set on the basis of the internal resistance DCR (which represents the state of health SoH). The internal resistance DCR of the lithium ion battery cell is measured during the method. This can be carried out continuously or at the start of a respective charging process. Alternatively or additionally, the internal resistance DCR can be read from a memory. Provision is advantageously made for the internal resistance determined at the end of a respective charging process to be stored.
In the healthy new state, the lithium ion battery cell 1 (cf.
After a plurality of charging processes, the lithium ion battery cell may have, for example, an internal resistance DCR which is between the first internal resistance threshold DCR1 and a second internal resistance threshold DCR2. The second internal resistance threshold DCR2 is 0.2 ohms, for example. The lithium ion battery cell has therefore aged. The lithium ion battery cell is now charged with a second charging current LS2. The second charging current LS2 is lower than the first charging current LS1 and is a constant 3 amperes, for example.
After further charging processes, the lithium ion battery cell may have, for example, an internal resistance DCR which is between the second internal resistance threshold DCR2 and a third internal resistance threshold DCR3. The third internal resistance threshold DCR3 is 0.3 ohms, for example. The lithium ion battery cell is now charged with a third charging current LS3. The third charging current LS3 is lower than the second charging current LS2 and is a constant 2 amperes, for example.
Close to the end of its service life, the lithium ion battery cell may have, for example, an internal resistance DCR which is above the third internal resistance threshold DCR3. In this case, the lithium ion battery cell is charged from now on with a fourth charging current LS4 which is a constant 1 ampere, for example. The situation just described illustrates the fact that a low charging current is set in each case in discrete steps (for example of 1 ampere each) when a predetermined internal resistance threshold is exceeded.
It is conceivable, in principle, for the internal resistance DCR of the lithium ion battery cell to increase on account of self-organization processes inside the lithium ion battery cell. For this situation, provision may be made for a higher charging current to be set when a predetermined internal resistance threshold is undershot.
The charging controller 20 is included, for example, in a charging station 101 which, in the present case, forms the battery cell charging system 100.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21195249.4 | Sep 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/073740 | 8/26/2022 | WO |
