WO2020055308A1

WO2020055308A1 - Vibration-assisted charging of electrified vehicle batteries

Info

Publication number: WO2020055308A1
Application number: PCT/SE2019/050838
Authority: WO
Inventors: Marzano FERNANDA
Original assignee: Scania Cv Ab
Priority date: 2018-09-11
Filing date: 2019-09-06
Publication date: 2020-03-19
Also published as: CN112673508A; SE542758C2; SE1851072A1; DE112019003787T5

Abstract

The present disclosure concerns an electrified vehicle (301, 401, 501) comprising:. a battery pack (303, 403, 503) adapted to be connectable to a power supply (311, 411, 511) for charging, wherein the battery pack comprises a plurality of battery cells;. a vibration-generating device (305, 415,517) arranged externally to the battery pack and arranged to produce vibration of the plurality of battery cells when the vibration-generating device is in a vibrational operative state; and. a control unit (307, 407, 507), wherein the control unit is configured to ensure that the vibration generating device is in a vibrational operative state at least during a period of a duration of charging of the battery pack; wherein the vibration-generating device is arranged to perform a function besides producing vibration when in a primary operative state. The present disclosure further concerns a method of charging a battery pack of such an electrified vehicle.

Description

VIBRATION-ASSISTED CHARGING OF ELECTRIFIED VEHICLE BATTERIES

TECHNICAL FIELD

The present invention relates to an electrified vehicle arranged to provide for rapid charging of the vehicle battery. The invention further relates to a method of charging the vehicle battery in such an electrified vehicle.

BACKGROUND ART

There is an ongoing trend towards electrification in the vehicle industry, in part to address the challenges posed by ever-stricter regulation of tailpipe emissions. As electric motors are increasingly used as a primary propulsion system for vehicles, batteries having larger capacities are required in order to provide an extended all-electric range or "electrical autonomy".

A factor limiting more widespread adoption of extensively electrified vehicles is the time it takes to charge batteries having larger capacities. As an example, it typically takes several hours to fully charge a plug-in hybrid electric car using a home charger. Charging time may be decreased by using specific charging infrastructure that can provide higher charge rates.

However, the charge rate (C-rate) achievable is limited not only by availability of

infrastructure, but also the chemistry utilized in the battery cells which fundamentally limits the achievable or optimal charging rate.

Modern hybrid or full-electric vehicles typically use lithium ion batteries. Charging using a high C-rate depletes the concentration of lithium ions available for insertion near the electrode surface since the diffusion of lithium ions in the electrolyte is too slow, causing a

concentration gradient to develop near the surface. Even if lithium ions are available in the bulk of the electrolyte, they are not accessible to the redox reactions taking place at the electrode. Mass transport by diffusion is the dominant process in the electrolyte for most electrochemical cells. If time is given, the developed concentration gradient disappears as new lithium ions diffuse to the electrode surface, and the insertion reactions can continue. The slow diffusion rate of lithium ions in the electrolyte and in the active materials increases the different polarizations in the cell (concentration, ohmic and activation). This results in a voltage decrease related to the C-rate of the charge procedure, leading to overpotential and associated electrolyte degradation, or simply leading to capacity losses since the cut-off voltage will be reached earlier. Moreover, long term charging at high C-rates leads to an increase in the cell temperature, with a corresponding increase in temperature-related degradation processes in the cell. Although described herein relative to lithium ion cells, similar concentration gradients may occur in any electrochemical cell, leading to similar problems with cell degradation and sub-optimal capacity. A number of means have been proposed to address these problems. For example, mixed charging protocols are known, where the battery is fast charged for some short period until some predetermined state of charge (SOC) and then further charged at a slower rate. Such protocols giving time for the concentration gradient to disappear.

US 5436548 describes battery charging and discharging systems in different embodiments. The battery charging system comprises a power supply and a means for vibrating the battery. The vibrating means may be located in the battery itself or external to the battery and electrically connected to the power supply. The vibrating means vibrates the battery during charging in order to improve the deliverable capacity of the battery. In another embodiment, a battery discharging system is described. Here, the battery is vibrated during discharge in order to increase the usable capacity. In the battery discharging system, the source of the vibration may be located in the battery package itself, or in a load or electrical device that is being powered by the battery.

There remains a need for improved means and methods of charging vehicle battery packs.

SUMMARY OF THE INVENTION

The inventor of the present invention has identified a number of shortcomings with prior art means and methods of charging vehicle battery packs. Standard fast charging accelerates the aging of batteries, as described in the background section, and reduces the obtainable capacity of the battery pack. Methods based on mixed fast/slow charging protocols do not allow continuous usage of high charging rates, nor do they fully charge batteries at high rates, nor can they provide fast charging for batteries at low temperatures where lithium ion transport is even slower, irrespective of charge protocol. Known methods utilizing vibrating means when charging batteries, such as in US 5436548, require dedicated vibrating means in the battery or electrically connected to the battery power supply. Such dedicated vibration means increase the weight and complexity of the battery charging system, thus increasing cost and reducing deliverable energy per unit weight, which are key considerations in producing electrified vehicles. US 5436548 also discloses a battery discharging system whereby the source of vibration may be located in a load or electrical device that is being powered by the battery. However, this discharging system is not envisaged in US 5436548 to be used during charging of the battery, presumably because if the vibrating means was to be used during charging it would constitute an undesirable parasitic load on the battery that simultaneously discharges the battery as it is being charged.

The inventor has identified the need for a means for charging a battery pack of an electrified vehicle that may allow for extended charging at high C-rates, even at lower temperatures, and that does not require the use of vibration means solely dedicated to the task of facilitating charging of the battery.

It is therefore an object of the present invention to provide a means for charging a battery pack of an electrified vehicle that addresses one or more of these concerns, thus helping to overcome or at least alleviate some of the above-mentioned shortcomings.

This object is achieved by an electrified vehicle as disclosed in the appended claims.

The electrified vehicle comprises: a battery pack adapted to be connectable to a power supply for charging, wherein the battery pack comprises a plurality of battery cells; a vibration-generating device arranged externally to the battery pack and arranged to produce vibration of the plurality of battery cells when the vibration-generating device is in a vibrational operative state; and a control unit, wherein the control unit is configured to ensure that the vibration generating device is in a vibrational operative state at least during a period of a duration of charging of the battery pack; wherein the vibration-generating device is arranged to perform a function besides producing vibration when in a primary operative state.

The electrified vehicle accelerates the mass transport in the battery cells by adding motion to the system during charge, providing convective mass transport and making the mass transport less dependable of the slow diffusion of ions. By adding motion, the charge rates are not limited to the same extent by concentration gradients. This not only allows repeated fast charging, but also to fast charge at lower temperatures where diffusion is slowed further.

The electrified vehicle utilizes a vibration-generating device that is arranged to perform a function besides producing vibration when in a primary operative state. This further function may for example be to assist in propelling the vehicle, to assist in steering the vehicle or to assist in improving the road characteristics of the vehicle. By utilizing such a vibration- generating device that already has a pre-existing function in an electrified vehicle, charging of the battery pack may be improved while to some extent avoiding the increases in weight, cost and complexity of known solutions.

The primary operative state may be a vibrational operative state, that is to say that the vibration-generating device may produce vibration while performing its primary function. Internal combustion engines, for example, tend to vibrate to some extent when operative.

This allows the battery cells to be vibrated in a simple, robust and cost-effective manner, since the device used to do so is already present and producing vibration as a by-product of its normal operation to some extent.

The primary operative state may generate substantially no vibration. This allows a precise control of the vibration of the battery cells, since vibration of the vibration-generating device does not occur inadvertently, but only by purposeful use of a vibrational operative state.

The vibration-generating device may be arranged to have a secondary operative state that is a vibrational operative state, the secondary operative state being configured to provide an increased level of vibration of the plurality of battery cells, relative to the primary operative state. This means that in the instance where the primary operative state produces vibration that a greater amount of vibration is produced in the secondary operative state, whereas when no vibration is produced in the primary operative state, the secondary operative state serves to produce vibration. This allows a greater degree of control of the vibration that the battery cells are subjected to.

The electrified vehicle may further comprise a mechanical linkage arranged to be actuated when the vibration-generating device is in the secondary operational state in order to produce vibration of the plurality of battery cells. This allows for convenient vibration of the battery cells by a device which may normally produce mechanical output but not necessarily vibration. The vibration-generating device may be an internal combustion engine. Since internal combustion engines tend to vibrate to some extent when in use, this allows the battery cells to be vibrated in a simple, robust and cost-effective manner, since the device used to do so is already present and producing vibration as a by-product of its normal operation. Furthermore, since the internal combustion engine is supplied with a separate source of energy (fuel), it does not represent a parasitic load on the battery or charging apparatus when charging the battery.

The vibration-generating device may be one or more electric motors, or one or more actuators in an active suspension system or power steering system. Such components may be capable of producing precisely-controlled vibration of the battery cells. The electrified vehicle may be a hybrid electric vehicle. Hybrid vehicles may comprise both batteries requiring charging, as well as an internal combustion engine that may be used to generate vibration. The present invention is thus readily applicable to such vehicles.

Each battery cell may comprise a liquid electrolyte. Liquid electrolyte cells are well-established and the mass transport properties of the electrolytes are well-modelled and known to be susceptible to improvement by the present invention. Each battery cell may be of the lithium- ion type. Lithium-ion batteries are commonly used in electrified vehicles.

The objects above are also achieved by a method of charging a battery pack of an electrified vehicle according to the appended claims. The battery pack comprises a plurality of battery cells, and the electrified vehicle comprises a vibration-generating device. The vibration generating device is arranged externally to the battery pack and is arranged to produce vibration of the plurality of battery cells when in a vibrational operative state, and is arranged to perform a function besides producing vibration when in a primary operative state. The method comprises the steps: arranging the battery pack in connection to a power supply for charging; charging the battery pack for a duration; and operating the vibration-generating device in a vibrational operative state at least during a period of a duration of charging of the battery pack. As described above, by vibrating the battery cells using the vibration-generating device during charging, the charge properties of the battery are improved.

The vibration-generating device may be operated in a secondary operative state which is a vibrational operative state at least during a period of a duration of charging of the battery pack. When the vibration-generating device is an internal combustion engine, the internal combustion engine may be operated without propelling the electrified vehicle during a period of a duration of charging of the battery pack. This allows charging from a stationary external charging device, for example a charging station, while using the internal combustion engine as a vibration-generating device. The vibration-generating device may be operated in a vibrational operative state during multiple periods during a duration of charging of the battery pack. This may allow the charging of the battery back to be improved while avoiding excessive vibration of the battery pack, by only vibrating temporarily when insufficient mass transport has led to suboptimal charging properties. The vibration-generating device may operated in a vibrational operative state during a total period of at least 30% of a duration of charging of the battery pack, such as at least 50% of a duration of charging of the battery pack, or such as at least 70% of a duration of charging of the battery pack, or such as at least 90% of a duration of charging of the battery pack. By vibrating the battery cells during charging for a suitable period the charging may be improved while avoiding excessive vibration of the battery cells and other vehicle components.

Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which:

Fig. 1 schematically illustrates the obtainable capacity of a battery at various charge rates.

Fig. 2 is a flow diagram schematically illustrating a method of charging a battery pack of an electrified vehicle.

Fig. 3 schematically illustrates an electrified vehicle according to an embodiment of the invention.

Fig. 4 schematically illustrates an electrified vehicle according to another embodiment of the invention.

Fig. 5 schematically illustrates an electrified vehicle according to a further embodiment of the invention.

DETAILED DESCRIPTION

The present disclosure is directed to an electrified vehicle comprising a battery pack, a vibration generating device and a control unit.

Electrified vehicle By electrified vehicle it is meant any vehicle that uses an electric motor to propel a vehicle to some extent. This includes all-electric vehicles such as battery electric vehicles, as well as hybrid electric vehicles such as plug-in hybrids, full hybrids and mild hybrids. The electrified vehicle may preferably be a plug-in vehicle such as a battery electric vehicle or plug-in hybrid. The vehicle may be any type of vehicle including but not limited to heavy vehicles such as trucks or buses, light commercial vehicles, motor cars and motorcycles.

Battery pack

The battery pack in electrified vehicles is typically used to power a propulsive electric motor in the electrified vehicle. A battery pack typically comprises a plurality of battery modules, where each module comprises a plurality of individual battery cells. The battery pack typically further comprises controllers such as battery- and thermal management systems and a housing to encase all of the battery pack components. The battery pack is adapted to be connectable to a power supply for charging. This power supply may be an external power supply, such as a charging station, or an internal power supply, such as a generator. The battery pack may use any cell chemistry, such as Li-ion or NiMH cells, but preferably may be of the Li-ion type. The battery cells may use solid or liquid electrolyte, but liquid electrolytes are preferred due in part to widespread commercial availability, as well as the ease of inducing convective mass transfer in the liquid electrolyte.

Vibration-generating device

The vibration-generating device is arranged externally to the battery pack. By vibration generating device it is meant a device that is the source of the mechanical energy that results in vibration of the battery pack/cells. That is to say that the vibration-generating device does not merely transmit an extraneously produced vibration such as road vibration, and thus the vehicle tyres, suspension and chassis are not to be considered as vibration-generating devices. The mere transmission of extraneously produced vibration would result in a system having very limited utility (for example requiring motion of the vehicle), as well as most likely not producing sufficient vibration even in the most favourable circumstances. The vibration-generating device is arranged to perform a function besides producing vibration when in a primary operative state, and is arranged to produce vibration of the plurality of battery cells when in a vibrational operative state. By "arranged to perform a function besides producing vibration when in a primary operative state" it is meant a device that fulfils a pre-existing requirement in electrified vehicles over and above the function of producing vibration of the plurality of battery cells when the device is in operation. The primary function of the vibration-generating device may, for example, be to assist in propelling the vehicle, assist in steering the vehicle, or assist in maintaining good handling of the vehicle. The term "besides" is intended to encompass "other than" as well as "together with", i.e. the vibration generating device may produce vibration when in the primary operative state, but does not necessarily do so.

By "arranged to produce vibration of the plurality of battery cells when in a vibrational operative state" it is meant that when in the vibrational operative state the vibration-generating device causes the battery cells to vibrate. Note that the vibration-generating device itself does not necessarily vibrate when in the vibrational operative state, although it may do so. For example the vibration-generating device may itself vibrate and transmit this vibration to the battery cells via other vehicle components such as the chassis. However, it is also envisaged that the vibration generation device may produce a motion, such as a reciprocal motion or rotational motion, that may be converted to a vibrational motion of the battery cells via a linkage.

The vibration-generating device may, for example, be selected from a list of devices including, but not limited to: an internal combustion engine, an electric propulsion motor, an actuator in an active suspension system, or an actuator in a power steering system. Actuators may be hydraulic, electro-hydraulic or electric actuators.

The vibration-generating device may produce vibration as a side-effect of its primary function in the primary operative state. For example, internal combustion engines inevitably produce some degree of vibration whenever operational. Such vibration-generating devices may be arranged to have a secondary operative state whereby an augmented degree of vibration is produced. For example, in the case of an internal combustion engine it is known that the vibration produced is greater during stopping and/or starting of the engine, or whenever the engine is not firing equally on all cylinders, and therefore a second operative state may be provided that utilizes such effects during charging of the battery.

Alternatively, the vibration-generating device may not generally produce significant vibration in the primary operative state. For example, this is the case with actuators in power steering or active suspension systems. In such a case, the vibration-generating device may be arranged to provide a secondary operative state whereby vibration of the battery cells is produced. This may be achieved by utilizing the vibration-generating device to produce relatively non-specific vibration of at least a part of the vehicle, for example by using active suspension actuators to vibrate the part of the vehicle closest to the battery pack during charging. However, specific vibration of the battery pack, individual battery modules, or individual battery cells may be achieved by arranging a linkage between the vibration-generating device and battery pack/modules/cells that may be actuated during charging of the battery. The linkage may for example be a mechanical linkage between the vibration-generating device and the battery pack/modules/cells. The mechanical linkage may be arranged to be actuated only when the vibration-generating device is in the secondary operative state, thus potentially avoiding hindering the function of the vibration-generating device in its primary operative state.

Control unit

The control unit is configured to ensure that the vibration-generating device is in a vibrational operative state at least during a period of a duration of charging of the battery pack. The control unit may also be configured to monitor and regulate charging of the battery pack.

Vibration of the battery cells

Vibration of the battery pack, battery modules or battery cells may be detected using one or more sensors, for example accelerometers such as piezoelectric or MEMS accelerometers. Alternatively, vibration of the battery cells during charging may be detected indirectly by observing the effect on the charge behaviour of the battery pack.

Figure 1 schematically illustrates the obtainable capacity of a battery (% Capacity - y axis) at various charge rates (C - x axis). The charge rate C is the rate necessary to charge or discharge a battery relative to its maximum capacity. 1C is the rate necessary to discharge or charge a battery in one hour, so if the battery has a capacity of 50Amp hour 1C would be a rate of 50 Amps, whereas 2C would be a rate of 100 Amps. Line 101 illustrates typical charge behaviour in a battery having only diffusive mass transfer within the electrolyte, i.e. a battery that is stationary. Line 103 illustrates typical charge behaviour for a battery having both diffusive and convective mass transport mechanisms in the electrolyte, i.e. a battery being vibrated. As can be seen from Figure 1, the maximum capacity is obtainable only at low C-rates for both vibrated (line 103) and non-vibrated (line 101) batteries. For lithium ion batteries having liquid electrolytes this is typically in the range of about 0.5 or lower. In a non-vibrated battery (line 101) the obtainable capacity declines quite rapidly as the C-rate is increased. However, in a vibrated battery (line 103) the decline in obtainable capacity is less pronounced as the C-rate is increased, i.e. at higher C-rates vibrated batteries demonstrate improved charge performance as compared to non-vibrated (stationary) batteries.

Method of charging a battery pack

Figure 2 is a flow diagram schematically illustrating the method of charging the battery pack of the electrified vehicle. When charging the battery pack the following steps are performed: arranging the battery pack in connection to a power supply for charging (s201); charging the battery pack for a duration (s202); and operating the vibration-generating device in a vibrational operative state at least during a period of a duration of charging of the battery pack (s203). The power supply may be an external power supply, such as a charging station for electrified vehicles, or it may be an internal power supply, such as a generator in a series hybrid vehicle. If the power supply is an internal power supply, the battery pack may permanently or semi permanently be arranged in connection with the power supply.

Once the battery pack is arranged in connection with the power supply, charging may be initiated. As discussed above, the nominal charge duration for a battery pack charging at a rate of 1C is one hour, 2 hours for a charge rate of 0.5C, and so on.

During the charging duration, the control unit is active to ensure that the vibration-generating device is in a vibrational operative state at least at some period during charging. This may require the control unit to initiate a vibrational operative state, for example by switching on an internal combustion engine. However, in some instances a vibrational operative state may already be ongoing, for example in the case of a series hybrid vehicle whereby the internal combustion engine is operational in order to charge the battery pack. The vibration-generating unit may be placed in a vibrational operative state for substantially the entire duration of charging, such as at least 90% of the duration of charging of the battery pack. However, it may be sufficient to vibrate the battery cells for a shorter proportion of the duration of charging, such as at least 70%, at least 50% or at least 30%. The battery cells may be vibrated during a single period during charging, or vibration may be performed during multiple periods, such as a fixed number and duration of periods per charge or a fixed number and duration of periods per time unit. The total period is thereby the sum of the individual periods of vibration.

The control unit may also be arranged to monitor the charge characteristics of the battery pack and control the vibration of the battery cells based on the charge characteristics of the battery pack. In this manner, the battery cells need only be vibrated if the charge characteristics indicate that a substantial concentration gradient has developed in the electrolyte of the cells.

Charging may be performed at variable rates using a combined protocol of vibration and fast and slow charging. Charging may be performed for a fixed period of time, or charging may be halted when a specified current or voltage limit is reached.

The invention will now be further exemplified with reference to the illustrated embodiments.

Figure 3 schematically illustrates an electrified vehicle according to an embodiment of the invention. The electrified vehicle 301 is a hybrid electric vehicle comprising a battery pack 303, an internal combustion engine 305, control unit 307 and electric motor 309. The battery pack 303 is connected to a charge station 311 by a power cord 313. During charging the internal combustion engine 305 is periodically started, operated and stopped by the control unit 307 in order to produce vibrations. These vibrations are propagated through the vehicle to the battery pack 303, thus vibrating the battery cells within the battery pack 303. The vehicle transmission (not shown) may be decoupled from the driveline during this procedure in order to operate the internal combustion engine 305 without propelling the vehicle 301.

Figure 4 schematically illustrates an electrified vehicle according to another embodiment of the invention. The electrified vehicle 401 is a battery electric vehicle comprising a battery pack 403, control unit 407 and electric motor 409. The electric vehicle further comprises an active suspension comprising electromechanic actuators 415. The battery pack 403 is connected to a charge station 411 by a power cord 413. During charging the electromechanic actuators 415 are systematically actuated by the control unit 407 in order to produce vibrations. These vibrations are propagated through the vehicle to the battery pack 403, thus vibrating the battery cells within the battery pack 403. Figure 5 schematically illustrates an electrified vehicle according to a further embodiment of the invention. The electrified vehicle 501 is a battery electric vehicle comprising a battery pack 503, control unit 507 and electric motor 509. The electric vehicle further comprises power steering comprising electromechanic actuator 517. Mechanical link 519 couples the electromechanic actuator 517 to the housing of the battery pack 503 during charging. The battery pack 503 is connected to a charge station 511 by a power cord 513. During charging the electromechanic actuator 517 is periodically actuated by the control unit 507 in order to produce motion which is conveyed by mechanical link 519 to the housing of the battery pack 503, thus vibrating the battery cells within the battery pack 503.

Claims

1. An electrified vehicle (301, 401, 501) comprising: a battery pack (303, 403, 503) adapted to be connectable to a power supply (311, 411, 511) for charging, wherein the battery pack comprises a plurality of battery cells; a vibration-generating device (305, 415, 517) arranged externally to the battery pack and arranged to produce vibration of the plurality of battery cells when the vibration generating device is in a vibrational operative state; and a control unit (307, 407, 507), wherein the control unit is configured to ensure that the vibration-generating device is in a vibrational operative state at least during a period of a duration of charging of the battery pack; wherein the vibration-generating device is arranged to perform a function besides producing vibration when in a primary operative state.

2. An electrified vehicle according to claim 1, wherein the primary operative state is a vibrational operative state.

3. An electrified vehicle according to claim 1, wherein the primary operative state generates substantially no vibration.

4. An electrified vehicle according to any one of the preceding claims, wherein the vibration generating device is arranged to have a secondary operative state that is a vibrational operative state, the secondary operative state being configured to provide an increased level of vibration of the plurality of battery cells, relative to the primary operative state.

5. An electrified vehicle according to claim 4, wherein the electrified vehicle further comprises a mechanical linkage (519) arranged to be actuated when the vibration generating device (517) is in the secondary operational state in order to produce vibration of the plurality of battery cells.

6. An electrified vehicle according to any one of the preceding claims, wherein the vibration generating device is an internal combustion engine (305).

7. An electrified vehicle according to any one of claims 1-5, wherein the vibration-generating device is one or more electric motors, or one or more actuators in an active suspension system (415) or power steering system (517).

8. An electrified vehicle according to any one of the preceding claims, wherein the electrified vehicle is a hybrid electric vehicle.

9. An electrified vehicle according to any one of the preceding claims, wherein each battery cell comprises a liquid electrolyte.

10. An electrified vehicle according to any one of the preceding claims, wherein each battery cell is of the lithium-ion type.

11. A method of charging a battery pack (303, 403, 503) of an electrified vehicle (301, 401, 501), wherein the battery pack comprises a plurality of battery cells, and wherein the electrified vehicle comprises a vibration-generating device (305, 415, 517), the vibration generating device being arranged externally to the battery pack and being arranged to produce vibration of the plurality of battery cells when in a vibrational operative state, and being arranged to perform a function besides producing vibration when in a primary operative state, wherein the method comprises the steps: arranging the battery pack in connection to a power supply (311, 411, 511) for charging; charging the battery pack for a duration; and operating the vibration-generating device in a vibrational operative state at least during a period of a duration of charging of the battery pack.

12. A method according to claim 11, wherein the vibration-generating device is operated in a secondary operative state which is a vibrational operative state at least during a period of a duration of charging of the battery pack.

13. A method according to any one of claims 11-12, wherein the vibration-generating device is an internal combustion engine (305), and wherein the internal combustion engine is operated without propelling the electrified vehicle during a period of a duration of charging of the battery pack.

14. A method according to any one of claims 11-13, wherein the vibration-generating device is operated in a vibrational operative state during multiple periods during a duration of charging of the battery pack.

15. A method according to any one of claims 11-14, wherein the vibration-generating device is operated in a vibrational operative state during a total period of at least 30% of a duration of charging of the battery pack, such as at least 50% of a duration of charging of the battery pack, such as at least 70% of a duration of charging of the battery pack, such as at least 90% of a duration of charging of the battery pack.