WO2020117113A1

WO2020117113A1 - Battery pack comprising thermal management system for generating vibration

Info

Publication number: WO2020117113A1
Application number: PCT/SE2019/051198
Authority: WO
Inventors: Fernanda MARZANO
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2018-12-07
Filing date: 2019-11-26
Publication date: 2020-06-11
Anticipated expiration: 2021-06-07
Also published as: EP3891837A4; EP3891837A1; SE543069C2; SE1851524A1; CN113039676A; CN113039676B

Abstract

The present disclosure further concerns a method of charging such a battery pack, and an electrified vehicle comprising such a battery pack. The present disclosure concerns a battery pack (303) for an electrified vehicle (301). The battery pack comprises: - a plurality of battery cells (505); and - a thermal management system (400) comprising a heat transfer element (403). The heat transfer element (403) comprises a flow channel (507) and is arranged to provide heat transfer from the plurality of battery cells (505) to a heat transfer medium whenever a heat transfer medium flows through the flow channel (507). The battery pack (303) is arranged to produce vibration of the plurality of battery cells (505) via vibration of the heat transfer element (403) whenever a heat transfer medium flows through the heat transfer element (403). The present disclosure further concerns a method of charging such a battery pack (303), and an electrified vehicle (301) comprising such a battery pack (303).

Description

Battery pack comprising thermal management system for generating vibration

TECHNICAL FIELD

The present invention relates to a battery pack for an electrified vehicle. The invention further relates to a method of charging the battery pack.

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 give 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 for 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 a battery pack for an electrified vehicle as disclosed in the appended claims.

The battery pack comprises: a plurality of battery cells; and a thermal management system comprising a heat transfer element. The heat transfer element comprises a flow channel and is arranged to provide heat transfer from the plurality of battery cells to a heat transfer medium whenever a heat transfer medium flows through the flow channel. The battery pack is arranged to produce vibration of the plurality of battery cells via vibration of the heat transfer element whenever a heat transfer medium flows through the heat transfer element. The battery pack 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 battery pack utilizes a pre-existing and necessary component, i.e. the thermal

management system of the battery pack, in order to achieve vibration. By utilizing a component that already serves a purpose in the battery pack, charging of the battery pack may be improved while to some extent avoiding the increases in weight, cost and complexity of known solutions.

Further advantages of utilizing vibration to improve electrolyte mass transport in the battery are that the extent of lithium plating may be reduced, and more uniform cooling of the battery cells may be obtained.

The heat transfer element may take any one of a variety of forms. The heat transfer element may be a tube element wound in a serpentine path between cells in the plurality of battery cells. The heat transfer element may be a laminar element arranged between cells in the plurality of cells. The heat transfer element may be a superficial element arranged in contact with an outer surface of the plurality of cells. All of these forms of heat transfer element are utilized in commercially available battery packs and are thus viable means of regulating the temperature of the battery cells.

The heat transfer element may be arranged in proximity to a terminal of each battery cell. Thermal regulation via the terminal area may allow for a more uniform thermal regulation of the battery cells. Alternatively, or in addition, the heat transfer element may be arranged distal to a terminal of each battery cell. Thermal regulation distal to the terminal may facilitate packing of the battery pack in a space-efficient and safe manner.

The thermal management system may be a single-phase thermal management system utilizing a liquid heat transfer medium. Single-phase systems have the benefit of being simple, robust and require few components. Alternatively, the thermal management system may be a two- phase thermal management system. Two-phase systems may provide greater heating/cooling power.

The flow channel may comprise internal pivotable elements arranged to produce vibration by collision with an internal surface of the flow channel whenever a heat transfer medium flows through the flow channel. Alternatively, or in addition, the flow channel may comprise an internal propeller arranged to rotate whenever a heat transfer medium flows through the flow channel. The propeller has in such case an asymmetric mass distribution about the propeller axis such that vibration of the heat transfer element is generated whenever the internal propeller rotates. Thus, vibration and improved mass transport in the electrolyte may be achieved by relatively simple mechanical means.

Further means of inducing vibration include introducing irregularities, such as a helical ridge (e.g. screw threads), onto the interior surface of the flow channel.

The battery pack or thermal management system may comprises a control unit.

The thermal management system may comprise a first valve arranged in fluid communication with the flow channel, wherein the first valve comprises a port arranged in fluid

communication with a source of air, and wherein the control unit is arranged to control the first valve in order to introduce air into the flow channel, thus producing vibration of the heat transfer element. Thus, vibration may be controllably achieved.

The thermal management system may comprise a flow-regulating device arranged to regulate a flow of heat transfer medium through the flow channel. The flow-regulating device may for example be a pump, compressor or a controllable valve arranged in the flow path of the flow channel. By arranged in the flow path of the flow channel it is meant arranged in the circuit that the heat transfer medium circulates within. This includes potentially, but not necessarily, arranged in the flow channel itself.

The control unit may be arranged to control the flow-regulating device in order to regulate the degree of vibration produced by the heat transfer element. By degree of vibration it is meant the properties of the vibration, such as the vibration frequency or amplitude. Thus, vibration may be utilized only when desired, therefore reducing the mechanical stress to which the battery pack components are exposed. The control unit may be arranged to control the flow-regulating device to produce a fluid- hammer effect in the flow channel, thus producing vibration of the heat transfer element. Thus, vibration may be achieved using few if any supplementary components.

According to another aspect of the invention, the objects above are achieved by an electrified vehicle comprising a battery pack as described herein.

According to a further aspect of the invention, the objects above are achieved by a method of charging a battery pack according to the appended claims. The method comprises the steps of: arranging the battery pack in connection to a power supply for charging;

charging the battery pack for a duration); and

providing a flow of heat transfer medium through the flow channel sufficient to produce vibration of the heat transfer element and plurality of battery cells, at least during a period of a duration of charging of the battery pack.

The objects above are further achieved by use of a thermal management system in a battery pack to generate vibration of a plurality of battery cells contained in the battery pack.

As described above, by vibrating the battery cells using the thermal management system during charging, the charge properties of the battery are improved.

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. 4a schematically illustrates a single-phase thermal management system;

Fig. 4b schematically illustrates a two-phase thermal management system;

Fig. 5a schematically illustrates an embodiment of the invention wherein the heat

transfer element is a tube element;

Fig. 5b schematically illustrates an embodiment of the invention wherein the heat

transfer element is a laminar element;

Fig. 5c schematically illustrates an embodiment of the invention wherein the heat

transfer element is a superficial element;

Fig. 6a schematically illustrates an embodiment of the invention wherein the flow

channel comprises a centrally-mounted pivotable element; Fig. 6b schematically illustrates an embodiment of the invention wherein the flow

channel comprises an internal mass-asymmetric propeller;

Fig. 7a schematically illustrates a thermal management system comprising a flow

regulating valve and control unit; and

Fig. 7b schematically illustrates a thermal management system comprising a three-way valve for introduction of air into the heat transfer element.

DETAILED DESCRIPTION

The present disclosure is directed to a battery pack for an electrified vehicle, and use thereof.

Electrified vehicle By electrified vehicle it is meant any vehicle that uses an electric motor to propel the 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 further comprises a thermal management system to avoid over- or underheating of the battery components and thus ensure optimal operation. Battery packs typically further comprises controllers such as battery- and thermal management control units, as well as a housing to encase all of the battery pack components. The battery pack is generally 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, Lithium metal, Na-ion or NiMH cells, but preferably may be of the Lithium (ion or metal) type. The battery cells may use solid or liquid electrolyte.

Thermal management system

The thermal management system of the battery pack is intended to maintain the battery cells within an optimal operational temperature window. This may involve cooling the cells during operation/charging, but may also involve heating the cells if the vehicle ambient temperature is low. The thermal management system may operate on a single-phase principle, i.e. a heat transfer medium is circulated in the system but does not typically change phase. Single phase systems may be based on a liquid heat transfer medium, such as water-glycol mixtures, or may be based on a gaseous heat transfer medium, such as air. The thermal management system may alternatively operate on a two-phase principle, i.e. the heat transfer medium changes phase during the heating/cooling operation. Suitable heat transfer media for two-phase systems include but are not limited to refrigerants such as R-134a. Advantages of a single-phase system are the robustness and simple construction of such systems. Two-phase systems comprise more components and are therefore more complex, but are capable of providing a greater heating/cooling capacity.

The thermal management system comprises one or more heat transfer elements arranged to provide heat transfer from a plurality of battery cells to a heat transfer medium. A single heat transfer element may be used to thermally regulate all cells in the battery pack, or multiple heat transfer elements may be used, e.g. one element per battery module. The heat transfer element is preferably located in close proximity to, or direct contact with, the cells or modules that it is intended to regulate. The heat transfer element may for example be in the form of: a tube element, i.e. a hose or pipe, wound in a serpentine path between cells or modules; a laminar element, i.e. a plate, arranged between cells or modules; or a superficial element, e.g. a base or housing wall, arranged in contact with an outer surface of the plurality of cells or modules. The heat transfer element(s) may be arranged in contact with a terminal (tab) portion of each cell or module, or may be arranged in contact with a portion of each cell or module remote from the terminals (tab). Terminal (tab) cooling may promote a more even temperature within the cells, but may in some instances be more difficult to implement in the battery pack.

Each heat transfer element comprises a flow channel through which the heat transfer medium may flow in order to remove or provide heat to the battery cells as required. At least the heat transfer elements of the thermal management system are integral to the battery pack. All further components, such as pumps, compressors, valves, condensers and/or radiators may be arranged integrally to the battery pack or may be arranged separately, but in fluid communication with the thermal management system components integral to the battery pack. For example, the thermal management system may typically be connected to or comprise a pump for circulating the heat transfer medium through the flow channel. The flow channel in turn is typically fluidly connected to a component capable of receiving heat from or providing heat to the heat transfer medium. Such components may include vehicle radiators or heat- producing vehicle components such as combustion engines. For example, the thermal management system may be arranged in fluid communication with a vehicle engine cooling system.

Means of vibrating the battery cells The battery pack is arranged to produce vibration of the heat transfer element whenever the heat transfer medium flows through the heat transfer element. This may be achieved in a variety of manners. For example, the flow channel of the heat transfer element may comprise movable elements that produce vibration as the heat transfer medium flows through the flow channel. Such movable elements may for example be one or more pivotable elements arranged internal to the flow channel and arranged to produce vibration by collision with an internal surface of the flow channel. For example, the flow channel may comprise one or more pivotable arms that may be centrally-mounted or wall-mounted in the flow channel. Such movable elements may alternatively or in addition be one or more internal propellers arranged in the flow channel and having an asymmetric mass distribution about the propeller axis. As the propeller rotates due to the flow of passing heat transfer medium, vibration is generated in the heat transfer element. Vibration may be induced by controllably introducing a gas, such as air, into the flow channel. Vibration may also be achieved by controlling the flow of heat transfer medium though the flow channel, using for example a flow-regulating device such as a valve, pump or compressor. The flow regulating device may for example be controlled to achieve a fluid-hammer effect in the flow channel, thus causing vibration. Further means of inducing vibration include introducing irregularities, such as a helical ridge (e.g. screw threads), onto the interior surface of the flow channel.

The flow regulating device may also be used in conjunction with other means of generating vibration in order to control the extent of vibration. For example, movable elements in the flow channel may be arranged to cause vibration only whenever heat transfer medium flow rate is above a threshold level, or only whenever a rate of change of heat transfer medium flow rate is above a threshold level, or only in a certain flow direction. This means that the thermal management system may be utilized in a non-vibrational mode, as well as in a vibrational mode when appropriate. For example, vibration may only be desirable during charging, whereas during operation of the battery pack it may instead be desirable to provide thermal management without vibration.

The thermal management system may comprise a control unit configured to ensure that a flow of heat transfer medium sufficient to produce vibration is provided through the flow channel at least during a period of a duration of charging of the battery pack. This may for example be achieved by controlling the flow-regulating device. The control unit may also be configured to monitor and regulate charging of the battery pack.

Effect of vibrating 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, located on the relevant component. 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 providing a flow of heat transfer medium through the flow channel sufficient to produce vibration of the heat transfer element and plurality of battery cells. The flow is provided 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, a flow of heat transfer medium sufficient to produce vibration is provided through the flow channel, at least at some period during charging. The flow of heat transfer medium sufficient to produce vibration may endure 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.

A control unit may 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 full electric vehicle comprising a battery pack 303, control unit 307 and electric motor 309. The battery pack 303 comprises a thermal management system 400 and is connected to a charge station 311 by a power cord 313. During charging, the heat transfer elements (not shown) in the battery pack 303 are vibrated by circulation of heat transfer medium. These vibrations are propagated to the battery cells (not shown) of the battery pack 303, thus vibrating the battery cells within the battery pack 303. Note that although the battery pack is illustrated as being located at a lower surface of the vehicle, the battery pack may be located at any suitable location in the vehicle, such as on the roof or in a suitable storage space.

Figure 4a schematically illustrates a single-phase thermal management system 400 for the battery pack 303. The thermal management system 400 comprises a heat transfer element 403 in the battery pack. Pump 405 and radiator 407 may constitute part of the battery pack 303 or they may be provided externally to the battery pack 303. Pump 405 circulates heat transfer medium through the heat transfer element 403 and radiator 407. Depending on ambient conditions and battery operating conditions, heat may be removed or provided to the battery cells via the heat transfer element 403 upon circulation of the heat transfer medium.

Figure 4b schematically illustrates a two-phase thermal management system 410 for the battery pack 303, based on a vapour-compression cycle. The two-phase thermal management system 410 is described herein as operating to cool the battery cells, but may equally be operated to heat the battery cells instead. The thermal management system 410 comprises a heat transfer element 403 in the battery pack. Compressor 415, condenser 417 and expansion valve 419 may constitute part of the battery pack 303 or they may be provided externally to the battery pack 303. Compressor 415 compresses vapour heat transfer medium and conveys the resulting superheated medium through the condenser 417. The condenser may be air-cooled, e.g. a radiator, or be liquid-cooled. The condenser 417 removes heat from the heat transfer medium, condensing the vapour to a liquid heat transfer medium. The liquid heat transfer medium then passes through expansion valve 419, leading to a mixture of liquid and vapour. This mixture is heated by passing through the heat transfer element 403, thus providing cooling of the battery cells and a vaporized heat transfer medium. The cycle then continues by passing the heat transfer medium through compressor 415 as previously described. Figures 5a-c schematically illustrate various forms the heat transfer element 403 may take in the battery pack 303. In figure 5a, the heat transfer element 403 is in the form of a tube winding around the plurality of battery cells 505. Flow channel 507 runs internally within the tube. The tube walls 509 may be designed to improve heat transfer between the battery and the heat transfer element. For example, they may be finned.

In Figure 5b the heat transfer element 403 is in the form of a plate arranged between battery cells 505. Space is shown between the cells 505 and the heat transfer element 403 for the sake of clarity, although in practice the cells 505 and heat transfer element 403 would be more tightly-packed. Flow channel (shown as a dotted line 507) runs internally within the plate.

In Figure 5c, the heat transfer element 403 is shown in the form of a base onto which the plurality of cells 505 are mounted. Flow channel (shown as a dotted line 507) runs internally within the base.

Figures 6a-b schematically illustrate some means by which movable elements internal to the flow channel may induce vibration. Figure 6a illustrates an arm 603 pivotably mounted centrally in flow channel 507. Side channels 608 allow a portion of the main flow (indicated by arrow 607) to be diverted and act upon a side of the arm 603, causing the arm 603 to swing (as illustrated by dotted line 605) and collide with the alternate side of the flow channel wall. Due to the symmetry of the side channels, one the arm 603 has swung, it will be acted on in the opposite direction by the side flow and return to its original position. Thus, the arm 603 swings side to side, colliding with the wall of the flow channel and causing vibration. The dimensions of the side channels 608 and flow rate through the flow channel determine the frequency and amplitude of vibration. Such vibration-generating devices are known in the art.

Figure 6b schematically illustrates a mass-asymmetric propeller 609, i.e. a propeller with asymmetrical weight distribution, arranged centrally in flow channel 507. Rotation of the propeller due to a flow of heat transfer medium through flow channel 507 will create vibration of the flow channel 507 due to the mass asymmetry of the propeller. The vibration will be generated as a function of flow, i.e. f(Q)=N wherein N is the rotational speed of the propeller and Q is the flow of heat transfer fluid. The relationship of Qto N depends on the exact propeller design, as well as on other factors such as hydraulic losses. The vibrational frequency depends on N, and the amplitude of the vibration depends on the weight distribution and N². Thus, altering the flow of heat transfer fluid past the propeller will alter the vibration amplitude and frequency. The propeller 609 may be designed to rotate only in a single flow direction, or may be designed to rotate more easily in one direction than in the other direction, or it may be designed to rotate equally regardless of flow direction.

Figures 7a and 7b schematically illustrate how vibration may be achieved in the thermal management system 400 using a control unit 715 in conjunction with valves 709 or 711. Figure 7a illustrates a thermal management system 400 as previously described in Figure 4a, but further comprising a controllable valve 709 and a control unit 715 arranged to control the valve 709 as well as pump 405. The flow of heat transfer medium in the system may be controlled using control unit 715 together with pump 405 and/or valve 709 in order to provide vibration as required, for example by controlling the rate, change in rate, or direction of flow through the heat transfer element 403. Additionally, vibration may be achieved in this system using a fluid- hammer effect by rapidly closing valve 709 whilst circulating heat transfer medium. In this manner, a pressure wave may be generated in heat transfer element 403 causing vibration of the heat transfer element. Figure 7b illustrates a thermal management system 400 as previously described in Figure 4a, but further comprising a controllable three-way valve 711 and a control unit 715 arranged to control the valve 711 as well as pump 405. The three-way valve 711 is connected to a source of air 731, such as ambient air supply or the compressed air supply of the vehicle. By using control unit 715 to control valve 711 in order to introduce air bubbles into the heat transfer fluid entering heat transfer element 403, vibration may be generated in heat transfer element 403.

Claims

1. A battery pack for an electrified vehicle, the battery pack comprising: a plurality of battery cells; and a thermal management system comprising a heat transfer element, wherein the heat transfer element comprises a flow channel and is arranged to provide heat transfer from the plurality of battery cells to a heat transfer medium whenever a heat transfer medium flows through the flow channel; wherein the battery pack is arranged to produce vibration of the plurality of battery cells via vibration of the heat transfer element whenever a heat transfer medium flows through the heat transfer element; characterized in that the flow channel comprises internal pivotable elements arranged to produce vibration by collision with an internal surface of the flow channel whenever a heat transfer medium flows through the flow channel.

2. A battery pack according to claim 1, wherein the heat transfer element is a tube element wound in a serpentine path between cells in the plurality of battery cells; or a laminar element arranged between cells in the plurality of cells; or a superficial element arranged in contact with an outer surface of the plurality of cells.

3. A battery pack according to any one of the preceding claims, wherein the heat transfer element is arranged in proximity to a terminal of each battery cell and/or wherein the heat transfer element is arranged distal to a terminal of each battery cell.

4. A battery pack according to any one of the preceding claims, wherein the thermal management system is a single-phase thermal management system utilizing a liquid heat transfer medium, or wherein the thermal management system is a two-phase thermal management system.

5. A battery pack according to any one of claims 1-4, wherein the flow channel comprises an internal propeller arranged to rotate whenever a heat transfer medium flows through the flow channel and having an asymmetric mass distribution about a propeller axis such that vibration of the heat transfer element is generated whenever the internal propeller rotates.

6. A battery pack according to any one of the preceding claims, wherein the battery pack comprises a control unit.

7. A battery pack according to claim 6, wherein the thermal management system comprises a first valve arranged in fluid communication with the flow channel, wherein the first valve comprises a port arranged in fluid communication with a source of air, and wherein the control unit is arranged to control the first valve in order to introduce air into the flow channel, thus producing vibration of the heat transfer element.

8. A battery pack according to claim 6, wherein the thermal management system comprises a flow-regulating device arranged to regulate a flow of heat transfer medium through the flow channel.

9. A battery pack according to claim 8, wherein the control unit is arranged to control the flow-regulating device in order to regulate the degree of vibration produced by the heat transfer element.

10. A battery pack according to claim 9, wherein the control unit is arranged to control the flow-regulating device to produce a fluid-hammer effect in the flow channel, thus producing vibration of the heat transfer element.

11. A battery pack according to any one of claims 8-10, wherein the flow regulating device is a pump or a second valve arranged in a flow path of the flow channel.

12. An electrified vehicle comprising a battery pack according to any one of claims 1-11.

13. A method of charging a battery pack according to any one of claims 1-11, the method comprising the steps: arranging the battery pack in connection to a power supply for charging (s201); charging the battery pack for a duration (s202); and providing a flow of heat transfer medium through the flow channel sufficient to produce vibration of the heat transfer element and plurality of battery cells, at least during a period of a duration of charging of the battery pack (s203).

14. Use of a thermal management system in a battery pack to generate vibration of a plurality of battery cells contained in the battery pack.