Lithium-ion battery cell balancing system and method, and battery charging device with lithium-ion battery cell balancing

Abstract

To provide a lithium-ion rechargeable battery charging system including lithium cell balancing and a lithium cell balancing method.SOLUTION: A battery charging device 10 includes a plurality of lithium-ion rechargeable battery cells 26A to 26D connected in series and a battery management system (BMS). The BMS includes a discharge field effect transistor (FET) 30 and a charge FET 32. A lithium-ion rechargeable battery charging system including a lithium cell balancing mode includes a lithium-ion rechargeable battery and a battery charging device 20 configured for charging the lithium-ion rechargeable battery. Cell balancing of the lithium-ion rechargeable battery cell of the lithium-ion rechargeable battery continues for a predetermined time from the start of the cell balancing mode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lithium-ion battery cell balancing system and method, and to a battery charging device comprising a lithium-ion battery cell balancing system and / or incorporating the lithium-ion battery cell balancing method of the present invention. [Background technology]

[0002] Currently, there are battery chargers for charging depleted or discharged lithium-ion rechargeable batteries (e.g., depleted or discharged lithium-ion rechargeable vehicle batteries). The mode of operation of these existing battery chargers is that while the battery charger is supplying current to a depleted or discharged lithium-ion rechargeable battery being charged, if the battery charger's lithium-ion rechargeable battery voltage reaches a lithium mode cutoff voltage (e.g., 14.6 V), even during soft start, the charging current is cut off and, after an appropriate fuel gauge time increment, the fuel gauge on the battery charger's display displays a solid green light (e.g., via a green LED on the fuel gauge).

[0003] Additionally, existing battery chargers cycle between lithium mode and standby mode while charging a depleted or discharged lithium ion rechargeable battery. Specifically, when a lithium ion rechargeable battery is being charged using a Battery Management System (BMS) and the lithium ion rechargeable battery cells become unbalanced, the battery charger cycles between lithium mode and standby mode.

[0004] This is because the Battery Management System (BMS) of a lithium-ion rechargeable battery monitors the voltage of each individual cell. If the lithium-ion rechargeable battery is charged to an excessively high voltage, the BMS opens the charge FET to prevent further charging of that particular lithium-ion rechargeable battery cell. Meanwhile, an internal resistor in the BMS is connected to slowly discharge the lithium-ion rechargeable battery cell. Once the excessively voltage lithium-ion rechargeable battery cell has discharged to a low level, the charge FET is closed again.

[0005] When the charge FET is open, there is still a diode that provides a discharge path for the lithium-ion rechargeable battery cell. This means that when a battery charger is connected to a lithium-ion rechargeable battery, the battery charger's internal voltage divider resistor network senses the voltage at the terminals and attempts to drive the charging voltage. Because the battery's charge FET is open, no current is detected by the battery charger and the battery charger returns to standby mode.

[0006] The battery charger senses the battery voltage, so every few seconds the battery charger gets the battery voltage and checks if it can supply current. When it is ready to supply current, the battery charger goes from standby mode to lithium mode. The battery charger will cycle between standby mode and lithium mode until the Battery Management System (BMS) closes the charge FET. Summary of the Invention

[0007] The present invention relates to a lithium-ion battery cell balancing system and / or method for charging depleted or discharged lithium-ion rechargeable batteries, wherein the battery charger comprises a lithium-ion battery cell balancing system and / or incorporates the lithium-ion battery cell balancing method of the present invention.

[0008] The lithium-ion battery balancing method includes multiple steps for balancing multiple lithium-ion rechargeable battery cells of a lithium-ion rechargeable battery depending on the type of battery charger (e.g., a constant current (CC) type battery charger or a constant voltage (CV) type battery charger).

[0009] The subject matter described herein also relates to methods for use in lithium-ion rechargeable battery charging systems and / or chargers that are integrated into a battery management system (BMS) and configured to charge lithium-ion rechargeable batteries.

[0010] A lithium ion rechargeable battery comprises a plurality of lithium ion rechargeable battery cells arranged electrically in series with one another. The lithium ion rechargeable battery cells may become unbalanced with one another due to differences in the containers and loads of the various lithium ion rechargeable battery cells. Specifically, during a charging operation, the voltages of the lithium ion rechargeable battery cells may differ relative to one another.

[0011] To maintain operation of the lithium-ion rechargeable battery cells within a safe voltage range, the lithium-ion rechargeable battery may be equipped with a battery monitoring system (BMS), whose role is to monitor the voltage of the lithium-ion rechargeable battery cells and open the discharge FET if any of the lithium-ion rechargeable battery cells of the lithium-ion rechargeable battery become undercharged, and open the charge FET if any of the lithium-ion rechargeable battery cells become overcharged.

[0012] A battery management system (BMS) may include a lithium-ion rechargeable battery cell balancing function according to the present invention. The battery management system (BMS) may monitor the voltage of individual lithium-ion rechargeable battery cells within a lithium-ion rechargeable battery. If a particular lithium-ion rechargeable battery becomes overcharged, the battery management system (BMS) places a small resistive load on the particular lithium-ion rechargeable battery cell to slowly drain the charge from the particular lithium-ion rechargeable battery cell. When the voltage of the particular lithium-ion rechargeable battery cell drops to a safety threshold, the resistive load on the particular lithium-ion rechargeable battery cell is removed.

[0013] During cell balancing of a lithium-ion rechargeable battery with unbalanced lithium-ion battery cells, the battery management system (BMS) will open and close multiple times, causing the battery management system (BMS) to slowly balance the internal lithium-ion rechargeable battery cells.

[0014] To charge a lithium-ion rechargeable battery, the final step is to stay in constant voltage (CV) mode and maintain a taper charge threshold at the battery charger terminals to allow time for the lithium-ion rechargeable battery's internal battery management system (BMS) to balance the cells. This time is called the lithium cell balancing time and may be set to, for example, 4 hours. However, this time is programmable and can be adjusted to a different duration (e.g., 6 hours or 8 hours).

[0015] During the lithium cell balance time, the battery charger is in constant voltage (CV) mode. During this time, the battery charger must be able to distinguish between the lithium-ion rechargeable battery's BMS opening the charge FET or the user disconnecting the charge cable from a depleted or discharged lithium-ion rechargeable battery that is being charged. If the charge FET is opened by the BMS, the battery charger must remain in lithium cell balance mode for balancing during the lithium cell balance time. If the user disconnects the battery charger from the lithium-ion rechargeable battery, the battery charger must go into standby mode.

[0016] While the lithium-ion rechargeable battery is in lithium cell balancing (LCB) mode, the output current of the battery charger is monitored. When the charging current drops below the minimum sense current level, the battery charger begins checking the battery voltage every second.

[0017] To check the voltage of the lithium-ion rechargeable battery, the battery charger opens the circuit from the battery charger's constant voltage supply to the lithium-ion rechargeable battery and measures the voltage of the lithium-ion rechargeable battery. If the voltage of the lithium-ion rechargeable battery drops below 10.5 V, the user has disconnected the battery charger cable from the lithium-ion rechargeable battery. If the voltage of the lithium-ion rechargeable battery is above 10.5 V, the Battery Management System (BMS) opens the charge FET and the battery charger connects the battery charger's constant voltage source to the lithium-ion rechargeable battery until the next 1-second lithium-ion rechargeable battery voltage check time interval. If the lithium-ion rechargeable battery begins drawing appreciable current again, the internal switch remains closed.

[0018] It is important to note that the freewheeling diode provides a current path for measurement, so when the charge FET opens, the battery charger can still measure the voltage of the Li-Ion rechargeable battery (minus the diode drop).

[0019] There are two modes of Lithium Cell Balancing (LCB). In the first Lithium Cell Balancing (LCB 1) mode, when the Lithium-Ion rechargeable battery cells are not significantly out of balance, the Battery Management System (BMS) does not open the charge FET during first Lithium Cell Balancing (LCB 1). In this mode, a constant current (CC) battery charger emulates a constant voltage (CV) battery charger. This is done by charging the Lithium-Ion rechargeable battery using a first soft-start current level until it reaches 14.6V. At that point, the current is turned off and the charger waits for the voltage to drop to 14.4V. Once the Lithium-Ion rechargeable battery reaches 14.4V (after a short delay), it switches back to the first soft-start current and repeats. So essentially, a constant current (CC) battery charger emulates a constant voltage (CV) battery charger by maintaining the battery voltage within a narrow range of 14.4V to 14.6V.

[0020] In Secondary Lithium Cell Balancing (2nd LCB) mode, the Li-ion rechargeable battery is far out of balance and the Battery Management System (BMS) opens the charge FET. The battery charger must detect whether the charge FET is open or if the user has disconnected it. Because an open charge FET has a body diode connection, the battery charger can still measure the battery voltage minus a diode drop. Therefore, even if the Battery Management System (BMS) opens the charge FET, the battery charger can still measure a battery voltage greater than 10.5V and still say that a Li-ion rechargeable battery is connected. Therefore, the battery charger must be able to detect when the charge FET has closed again. This is done by polling the impedance of the Li-ion rechargeable battery every second. While polling, the battery charger attempts to apply charge current. If the current is not accepted, it knows that the charge FET is still open. When the charge FET closes and the next charge poll is attempted, the battery charger knows the Li-Ion rechargeable battery will accept current and continues charging at the first soft-start level until the battery reaches 14.6V or the Battery Monitoring System (BMS) opens the charge FET. At that point, it enters the first Lithium Cell Balancing (1st LCB) mode. If the BMS opens, it repeats the second Lithium Cell Balancing (2nd LCB) mode.

[0021] This is achieved by either a first lithium cell balancing (first LCB) mode, a second lithium cell balancing (second LCB) mode, or a combination of the first lithium cell balancing (first LCB) mode after the second lithium cell balancing (second LCB) mode for the set time of cell balancing (LCB) operation.

[0022] For example, four hours is chosen for the battery charger, but this time is arbitrary. The total time required for the battery management system (BMS) to reach full cell balance depends on how far out of balance the lithium-ion rechargeable batteries are and what size balancing load is used by the battery management system (BMS). Both of these factors are not observable to the battery charger. [Brief explanation of the drawings]

[0023] [Figure 1] Schematic diagram of a lithium-ion rechargeable battery with a battery management system (BMS). [Figure 2] FIG. 1 is a plan view of a battery management system (BMS) showing the connections of the BMS to a lithium-ion rechargeable battery. [Figure 3] FIG. 1 is a perspective view of a battery management system (BMS) showing the connection of the BMS to a lithium-ion rechargeable battery. [Figure 4-1] Graph showing a G2 7AH (Ampere Hour) battery with 0.33AH (Ampere Hour) discharge from cell 1. [Figure 4-2] Graph showing a G2 7AH (Ampere Hour) battery with 0.33AH (Ampere Hour) discharge from cell 1 (7AH with 0.33AH discharge from cell 1). [Figure 5-1] Graph showing a G2 7AH (ampere hour) battery with 0.33A delivered to cell #1 (multiple charge cycles) (7AH plus 0.33A of additional charge added to cell 1). [Figure 5-2] Graph showing a G2 7AH (ampere hour) battery with 0.33A delivered to cell #1 (multiple charge cycles) (7AH plus 0.33A of additional charge added to cell 1). [Figure 6-1] Graph showing the above chart zoomed in to the 40-45 hour time frame (7AH plus an additional 0.33A charge added to cell 1). [Figure 6-2]Graph showing the above chart zoomed in to the 40-45 hour time frame (7AH plus an additional 0.33A charge added to cell 1). [Figure 7] Graph showing G2 cold start battery charging profile (potentially typical use) (7AH cold start battery after several months on the shelf) [Figure 8] Graph showing G2 short discharge to maintenance charge (balanced battery slightly discharged then charged at +100 hours maintenance). [Figure 9] Graph showing a zoomed-in time frame of the charging log above (balanced battery slightly discharged + 100 hour maintenance charge). [Figure 10] Graph showing a G10 7AH full charge with 0.45AH removed from cell 1 (G10 Firmv K 7AH with 0.45AH discharged from cell 1). [Figure 11] Graph showing competitor's Li-ion battery charging profile (Genius 2 Firmware Rev R charging a BTLI12A270CW Li-ion battery). [Figure 12] Graph showing competitor's Li-ion battery charging profile (Genius 2 Firmware Rev R charging ATZ-10). [Figure 13] Graph showing competitor's lithium-ion battery charging profile (ATZ-10 charging continuum. Charge until BMS no longer opens, then discharge and recharge. Note: BMS does not open on recharge, battery cells remain balanced). [Figure 14] Graph showing NOCO's Li-ion battery charging profile (Genius 5 Firmware Rev R charging an ETX12A battery). [Figure 15] Graph showing NOCO Li-ion battery charging profile (Genius 2 Firmware Rev R charging a NOCO NLP9). [Figure 16] Graph showing NOCO Li-ion battery charging profile (Genius 5 Firmware Rev R charging a NOCO NLP14). [Figure 17] A graph showing the charging profile of NOCO's Li-ion battery with Genius 2 Firmware Version S (Genius 2 Firmware Version 5 charging a 7AH Li-ion battery with LCB - cell 2 unbalanced). [Figure 18] Graph showing the charging profile for NOCO's Li-ion battery with Genius 10 Firmware P (G10 LCB Firmware Rev P 7AH 12V Lithium @ 25C, 1 cell overcharged). DETAILED DESCRIPTION OF THE INVENTION

[0024] 1, battery charging device 10 includes a positive battery cable 14 and a negative battery cable 16 connected to a lithium-ion rechargeable battery 20. For example, positive battery cable 12 may be connected to a positive terminal 22 of lithium-ion rechargeable battery 20 (e.g., using a positive battery clamp, not shown), and negative battery cable 14 may be connected to a negative battery terminal 24 of lithium-ion rechargeable battery 20 (e.g., using a negative battery clamp, not shown).

[0025] The lithium ion rechargeable battery 20 includes four lithium ion rechargeable battery cells 26A, 26B, 26C, and 26D electrically connected in series with one another, a Battery Management System (BMS) 28A connected to the four lithium ion rechargeable battery cells 26A, 26B, 26C, and 26D, a discharge FET 30, and a charge FET 32. As shown in FIG. 1, the discharge FET 30 and the charge FET 32 are electrically connected in series with the four lithium ion rechargeable battery cells 26A, 26B, 26C, and 26D.

[0026] 2, the battery management system (BMS) 28 includes a printed circuit board 34. The printed circuit board 34 includes a positive external battery terminal, or positive battery connection 34A, for an internal lithium-ion rechargeable battery, a negative external battery terminal 34B, and an internal lithium-ion negative battery terminal 34C.

[0027] As shown in FIG. 3, a battery management system (BMS) 28 is connected to the lithium-ion rechargeable battery 20 .

[0028] Battery charger 10 is configured and / or programmed in a particular manner to charge lithium-ion rechargeable batteries 20. For example, battery charger 10 includes a lithium-ion rechargeable battery cell balancing mode or function (i.e., lithium cell balance).

[0029] For example, battery charger 10 operates as follows: If the lithium-ion rechargeable battery voltage reaches the lithium mode cutoff voltage (e.g., 14.6V) while battery charger 10 is supplying current to a depleted or discharged lithium-ion rechargeable battery 20, even in soft-start mode, battery charger 10 enters Lithium Cell Balance (LCB) mode, for example, four hours. LCB mode is indicated by the 25%, 50%, and 75% fuel gauge LEDs on the battery charger 10 display, with the 100% LED illuminated (i.e., similar to some kind of gravity optimization).

[0030] During lithium cell balancing (LCB) mode, battery charger 10 cuts off the charging current when the battery voltage reaches the cutoff voltage. Battery charger 10 continues to monitor the battery voltage, and when the battery voltage drops to 14.4V, battery charger 10 resumes charging at the lowest soft-start current (e.g., half the lowest soft-start current if the temperature is below 0°C). Battery charger 10 cycles on and off multiple times as the battery voltage increases to 14.6V and then drops to 14.4V. Battery charger 10 turns off after reaching 14.6V for a predetermined time interval (e.g., 1 minute) before allowing battery charger 10 to turn on again, even if the battery voltage drops below 14.4V.

[0031] After a predetermined time interval (eg, 4 hours) in lithium cell mode, the battery charger 10 will stop charging and the fuel gauge on the battery charger 10 display will show 100%.

[0032] (Lithium cell balancing mode with BMS round trip) When charging a lithium-ion rechargeable battery (lithium mode), if the lithium-ion rechargeable battery's battery management system (BMS) opens but is unable to provide charging current before the battery voltage reaches 14.6 V, as indicated by the battery charger 10 measuring a voltage above the start voltage but below 14.6 V, the battery charger 10 will enter lithium cell balance mode and begin a four-hour timer. The fuel gauge will then illuminate the green 100% LED.

[0033] The battery charger 10 continues to poll the voltage of the lithium-ion rechargeable battery, but instead of going into standby mode between polling attempts, the battery charger 10 remains in lithium cell balancing (LCB) mode and the fuel gauge displays a green 100% LED (e.g., the green operating LED alternates between bright and dark).

[0034] When the battery charger 10 is in this current balancing mode, the battery management system (BMS) opens and closes randomly. The battery charger 10 continues to poll the voltage of the lithium-ion rechargeable battery when the battery management system (BMS) closes the FET, and when the FET closes, the battery charger 10 charges at the lowest soft-start current (e.g., 1 / 2 the lowest soft-start current below 0°C).

[0035] When the internal lithium-ion battery cells of a lithium-ion rechargeable battery are equalized to a state where the battery management system (BMS) does not open and the battery voltage rises to 14.6V, the battery charger 10 operates as described above, except that the four-hour timer is not reset.

[0036] After four hours in cell balance mode, the battery charger 10 will stop charging and the fuel gauge on the display of the battery charger 10 will show 100%. If the battery charger 10 does not detect that the battery voltage has dropped below the start voltage, the battery charger 10 will enter standby mode.

Claims

1. A lithium-ion rechargeable battery (LIRB) with lithium cell balancing, comprising: a plurality of lithium ion battery cells electrically connected in series; a battery management system connected to the plurality of lithium-ion battery cells and configured to control charging of the plurality of lithium-ion battery cells from an external battery charger; Equipped with the battery management system is further configured to charge the plurality of lithium-ion battery cells in a lithium cell balancing (LCB) mode; the LCB mode of the battery management system includes a first LCB mode; During the first LCB mode, the battery management system: charging the plurality of lithium-ion battery cells from the external battery charger; switching a charging current on and off to oscillate the voltage of the LIRB between a first voltage level and a second voltage level, thereby emulating constant voltage (CV) charging from the battery charger; LIRB.

2. The external battery charger is a constant current (CC) battery charger.

2. The LIRB of claim 1.

3. The LCB mode of the battery management system further includes a second LCB mode; During the second LCB mode, the battery monitoring system: Stopping charging of the plurality of lithium ion battery cells; reducing the voltage level of one or more of the plurality of lithium ion battery cells; 2. The LIRB of claim 1.

4. The battery management system a charging field effect transistor (FET) that enables charging of the plurality of lithium ion battery cells; a discharge field effect transistor (FET) that enables discharging of one or more of the plurality of lithium ion battery cells; 4. The LIRB of claim 3, comprising:

5. The battery management system maintains the charge FET closed during the first LCB mode.

5. The LIRB of claim 4.

6. The battery monitoring system opens the charge FET during the second LCB mode.

5. The LIRB of claim 4.

7. The battery management system is configured to open the discharge FET when any of the plurality of lithium-ion battery cells becomes undercharged.

5. The LIRB of claim 4.

8. The battery management system is configured to open the charging FET when any of the plurality of lithium-ion battery cells is overcharged.

5. The LIRB of claim 4.

9. The battery management system is configured to open and close the charge FET multiple times while the plurality of lithium-ion battery cells are balanced.

5. The LIRB of claim 4.

10. The battery management system monitoring a voltage level of each of the plurality of lithium ion battery cells; When one of the plurality of lithium ion battery cells becomes overcharged, placing a resistive load on the one cell to slowly discharge the one cell until the voltage level of the one cell reaches a lower threshold voltage level.

4. The LIRB of claim 3, configured as follows:

11. The battery management system is configured to maintain the LCB mode for a predetermined period of time.

2. The LIRB of claim 1.

12. The predetermined period is 4 hours.

12. The LIRB of claim 11.

13. The LIRB is configured to distinguish between the battery management system opening the charge FET and the external battery charger being disconnected.

7. The LIRB of claim 6.

14. A method for cell balancing a plurality of lithium ion battery cells in a rechargeable battery, comprising: emulating constant voltage (CV) charging from an external battery charger by switching a charging current on and off to oscillate a voltage of the rechargeable battery between a first voltage level and a second voltage level, thereby charging the plurality of lithium-ion battery cells from the external battery charger in a first lithium cell balancing (LCB) mode; Stopping charging of the plurality of lithium ion battery cells in a second LCB mode and reducing the voltage level of one or more of the plurality of lithium ion battery cells; A method comprising:

15. The method of claim 1, further comprising starting and stopping charging of the plurality of lithium ion battery cells multiple times while the plurality of lithium ion battery cells are balanced.

15. The method of claim 14.

16. Monitoring the voltage level of each of the plurality of lithium ion battery cells; When one of the plurality of lithium ion battery cells becomes overcharged, placing a resistive load on the one cell to slowly discharge the one cell until the voltage level of the one cell reaches a lower threshold voltage level; The method of claim 15 further comprising:

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