SE545442C2

SE545442C2 - A method of arranging cells in a battery pack and a battery pack

Info

Publication number: SE545442C2
Application number: SE2151437A
Authority: SE
Inventors: Narayna Murthy Sri Vishnu Gorantla
Original assignee: Northvolt Ab
Priority date: 2021-11-25
Filing date: 2021-11-25
Publication date: 2023-09-12
Also published as: WO2023094240A1; SE2151437A1

Abstract

This disclosure presents a method (100) of arranging a plurality of secondary cells (5) in a battery pack (1), wherein the battery pack (1) is configured such that the temperature of said plurality of secondary cells (5) may be regulated by a temperature regulating conduit (12). The method (100) comprises providing (110) a plurality of secondary cells (5), obtaining (120) at least one individual parameter of each secondary cell (5), the individual parameter comprising the individual internal resistance (R), and arranging (130) the plurality of secondary cells (5) in the battery pack (1). Arranging (130) the plurality of secondary cells (5) in the battery pack (1) comprises positioning at least some of the secondary cells (5) along the temperature regulating conduit (12) based on their individual internal resistance (R). The disclosure further presents a battery pack (1), a thermal management system (10) for regulating the temperature of secondary cells (5) within the battery pack (1), and a vehicle battery comprising said battery pack (1) and/or said thermal management system (10).

Description

A METHOD OF ARRANGING CELLS IN A BATTERY PACK AND A BATTERY PACK TECHNICAL FIELD The present disclosure generally pertains to arranging secondary cells in a battery pack, and more particularly to method of arranging a plurality of secondary cells in a battery pack, a battery pack comprising a plurality of secondary cells, a therrnal management system and a vehicle battery. BACKGROUND In addressing climate change, there is an increasing demand for rechargeable batteries, e.g. to enable electrification of transportation and to supplement renewable energy.

Such batteries typically comprise a number of cells, often referred to as secondary cells, arranged in one or more battery packs to provide the desired Voltage and current. The batteries are often cooled in order to avoid overheating and to prolong the life.

The document JP2012204141A discloses a battery device having a plurality of batteries and a voltage detecting device. Among the plurality of batteries, those having a relatively small capacity at a reference temperature are arranged on an upstream side of an air cooling passage, and those having a relatively large capacity at the reference temperature are arranged on a downstream side of the air cooling passage.

The document JP2007188715A discloses arranging cells having a high self-discharge near a center of a battery case, where the temperature is higher, and arranging cells having a low self- discharge near the entrance and exit of the battery case, where the temperature is lower.

To increase performance and also to decrease battery deterioration over time, preferably at a low cost, the design of the batteries can be optimized. SUMMARY It is in view of the above considerations and others that the embodiments of the present invention have been made. The present disclosure recognizes the fact that, at least in somescenarios, the service life a secondary battery may be impaired by the arrangement of the secondary cells in a battery pack. In addition, the arrangement of the secondary cells may fail to provide the best battery perforrnance.

The properties of the secondary cells that are to forrn a battery pack vary to some extent due to deviations in material and manufacture. For example, the individual intemal resistance, the individual capacity and the calendar loss of the secondary cells may vary.

According to a first aspect, the present disclosure provides a method of arranging a plurality of secondary cells in a battery pack, Wherein the battery pack is configured such that the temperature of said plurality of secondary cells may be regulated by a temperature regulating conduit. The method comprises providing a plurality of secondary cells, obtaining at least one individual parameter of each secondary cell, the individual parameter comprising the individual intemal resistance, and arranging the plurality of secondary cells in the battery pack. In accordance With the method, the arranging of the secondary cells comprises positioning at least some of the secondary cells along the temperature regulating conduit based on their individual intemal resistance.

By consciously positioning secondary cells along the temperature regulating conduit based on individual intemal resistance, the therrnal regulation of the secondary cells may be optimised. The optimisation may consist in minimising the temperature spread between secondary cells Within the battery pack, i.e. the differences in secondary cell temperatures. This optimisation may be obtained both When the secondary cells are cooled and When the secondary cells are heated, provided that the ﬂoW Within the temperature regulating conduit is reversed for cooling and heating, respectively.

In this Way, the battery performance may be maximised as cell performance may vary With cell temperature and a battery pack of even cell temperature may provide an optimal perforrnance. Also, an even cell temperature may result in even cell degradation and thus maximised life. The method is cost-effective to implement and does not require any structural modifications of the battery pack, such as additional therrnal regulation means, sensing means or processing IIICEIIIS .

During operation, i.e. charging and/or active discharging, secondary cells of relatively high intemal resistance may require more efficient cooling than secondary cells of relatively low internal resistance. Therefore, secondary cells of relatively high internal resistance may advantageously be positioned along the temperature regulating conduit such that they are more efficiently cooled than secondary cells of relatively low internal resistance.

In cold environments, secondary cells of relatively low internal resistance may require more efficient heating than secondary cells of relatively high internal resistance. Therefore, secondary cells of relatively low internal resistance may advantageously be positioned along the temperature regulating conduit such that they are more efficiently heated than secondary cells of relatively high intemal resistance.

The battery pack may be positioned adj acent the temperature regulating conduit, such that the temperature of said plurality of secondary cells may be regulated by the temperature regulating conduit by the cells being located close to the temperature regulating conduit. For example, heat may be removed from the cells by the heat being transferred to the temperature regulating conduit through an enclosure of the battery pack, preferably a thin enclosure that allows efficient heat transfer. Altematively, the temperature regulating conduit may pass through the battery pack. The temperature regulating conduit may at least partly be formed by an enclosure of the battery pack, or the temperature regulating conduit may be a pipe or hose that extends through the battery pack. In other words, the temperature regulating conduit may or may not be a part of the battery pack.

The method may include obtaining said at least one individual parameter of each secondary cell by performing individual cell measurements, or by reading previously produced measurement data conceming each cell. The previously produced measurement data may be attainable from a marking provided on each cell, or by the cell being provided with a unique identification to which measurement data is assigned in a database.

The secondary cells may be cylindrical secondary cells or so-called prismatic secondary cells.

The secondary cells may be lithium-ion cells.

The plurality of secondary cells may comprise a first secondary cell, a second secondary cell and a third secondary cell, wherein the first secondary cell has a higher intemal resistance than the second secondary cell that has a higher intemal resistance than the third secondary cell, and wherein the first, second and third secondary cells are positioned in order of intemal resistance along the temperature regulating conduit. The first, second and third secondary cells may be positioned in consecutive order of internal resistance along the temperature regulating conduit.

The first, second and third secondary cells may be positioned immediately next to one another.

Said at least one individual parameter may comprise the individual capacity. In other Words, the method may comprise obtaining individual parameters of each secondary cell, the individual parameters comprising the individual intemal resistance and the individual capacity. The positioning may be based on the individual intemal resistance and on the individual capacity of the secondary cells. In this Way, the therrnal regulation of the cells may be further optimised.

Said at least one individual parameter may comprise the individual calendar loss. The method may comprise obtaining individual parameters of each secondary cell, the individual parameters comprising the individual intemal resistance and the individual calendar loss. The positioning may be based on the individual intemal resistance and on the individual calendar loss of the secondary cells. In this Way, the therrnal regulation of the cells may be yet further optimised. Calendar loss may be referred to as a secondary cell°s susceptibility to degrade in capacity over time.

Altematively, the individual parameters may comprise the individual intemal resistance, the individual capacity and the individual calendar loss. The positioning may be based on the individual intemal resistance, on the individual capacity and on the individual calendar loss of the secondary cells.

The method may comprise positioning at least some of the secondary cells along the temperature regulating conduit based on at least two individual parameters, such as the intemal resistance and the capacity. The method may comprise giving or assigning these at least two parameters different Weights for the positioning. For example, the intemal resistance may be given more Weight than the capacity. In other Words, the intemal resistance may have a larger influence on the positioning of a secondary cell along then temperature regulating circuit than has the capacity.

The method may comprise giving said parameters, e.g. the intemal resistance, the capacity and/or the calendar loss, appropriate Weights depending on the intended application of the battery pack. For example, a battery pack that is intended for operation in vehicles that typically are expected to stand still for long periods may have a cell arrangement that effectively cools secondary cells with a high calendar loss. A battery pack that is intended for operation in a frequently running machine may have a cell arrangement that effectively cools secondary cells with a high internal resistance.

The method may comprise obtaining an individual cell therrnal rating of each secondary cell, the individual cell therrnal rating being dependent on the individual internal resistance and on the individual capacity and/or on the individual calendar loss. The positioning may be based on the individual therrnal rating. The therrnal rating may be deterrnined such that the therrnal regulation of the cells may be yet further optimised.

The method may obtain the individual cell therrnal rating by perforrning a calculation based on the obtained individual internal resistance, the individual capacity and/or the individual calendar loss, or by reading a previously calculated cell therrnal rating concerning each cell. The previously calculated cell therrnal rating may be attainable from a marking provided on each cell, or by the cell being provided with a unique identification to which a cell therrnal rating is assigned in a database.

A low internal resistance may lead to a high therrnal rating. A high capacity may lead to a high therrnal rating. A low calendar loss may lead to a high therrnal rating.

Obtaining the cell therrnal rating may comprise associating the respective individual parameter with a respective weighting constant. This corresponds to the above-mentioned assigning of the weights to the parameter. In a forrnula for deterrnining the therrnal rating, a respective parameter may be multiplied with a respective weighting constant.

The weighting constants may for example be selected such that the intemal resistance has a larger inﬂuence on the therrnal rating than has the capacity. It is typically believed beneficial to base the positioning of the secondary cells more on the individual intemal resistance than on the individual capacity.

The plurality of secondary cells may comprise a first secondary cell, a second secondary cell and a third secondary cell, wherein the first secondary cell has a lower therrnal rating than the second secondary cell that has a lower therrnal rating than the third secondary cell, and wherein the first secondary cell is positioned upstream relative to the second secondary cell that is positioned upstream relative to the third secondary cell, as seen in a cooling ﬂow direction of the temperature regulating conduit. In this example, a relatively low therrnal rating means that the secondary cell requires more efﬁcient cooling.

The first secondary cell may be positioned doWnstream relative to the secondary cell that may be positioned doWnstream relative to the third secondary cell, as seen in a heating ﬂoW direction of the temperature regulating conduit.

With the positioning of the above tWo paragraphs, the therrnal regulation of the secondary cells may be optimised both during heating and cooling by a ﬂoW Within the temperature regulating conduit that is reversed for cooling and heating, respectively. The temperature regulating conduit may form part of a temperature regulating circuit. The temperature regulating conduit may be configured for a coolant ﬂoW. The coolant may comprise ﬂuid and/or a liquid.

According to the method, the arranging of the secondary cells may comprise positioning at least some of the secondary cells along the temperature regulating conduit based on their individual intemal resistance, or based on their individual intemal resistance and individual capacity or based on their individual intemal resistance and individual capacity and individual calendar loss. The method may comprise positioning all the secondary cells along the temperature regulating conduit based on said parameters.

According to an altemative aspect, the present disclosure provides a method of arranging a plurality of secondary cells in a battery pack, Wherein the battery pack is configured such that the temperature of said plurality of secondary cells may be regulated by a temperature regulating conduit. The method comprises providing a plurality of secondary cells, obtaining at least one individual parameter of each secondary cell, the individual parameter comprising the individual calendar loss, and arranging the plurality of secondary cells in the battery pack. In accordance With the method, the arranging of the secondary cells comprises positioning at least some of the secondary cells along the temperature regulating conduit based on their individual calendar loss.

According to a second aspect, the present disclosure provides a battery pack comprising a plurality of secondary cells, Wherein the battery pack is conf1gured such that the temperature of said plurality of secondary cells may be regulated by a temperature regulating conduit and at least some of the secondary cells are positioned along the temperature regulating conduit based on their individual intemal resistance.

The advantages and further possible features of such a battery pack correspond to the ones of the above-described method of arranging a plurality of secondary cells in a battery pack, and Will therefore not be repeated. For example, the positioning may also be based on the individual capacity and/or the individual calendar loss as has been described.

The present disclosure further provides a therrnal management system comprising a battery pack as the one described above and a temperature regulating conduit, Wherein the battery pack is conf1gured such that the temperature of the plurality of secondary cells Within the battery pack may be regulated by the temperature regulating conduit, and comprising a bidirectional ﬂoW means for obtaining a cooling ﬂoW in a cooling ﬂoW direction through the temperature regulating conduit and a heating ﬂoW in a heating ﬂoW direction through the temperature regulating conduit, Wherein the heating ﬂoW direction is opposite to the cooling ﬂoW direction.

The therrnal management system may comprise a coolant that is adapted to ﬂoW through the temperature regulating conduit. The bidirectional ﬂoW means may be a pump, that may be adapted to selectively pump the coolant in the cooling ﬂoW direction and in the opposite heating ﬂoW direction. The therrnal management system may comprise a heat pump or similar temperature regulation means such that temperature of the plurality of secondary cells Within the battery pack may be selectively cooled or heated by the temperature regulating conduit. More precisely, the temperature regulation means may be adapted to selectively cool or heat the coolant.

The above-described battery pack and/or the above-described therrnal management system may be comprised in a vehicle battery for propelling a vehicle. The vehicle may for example be a fully electrically propelled vehicle or a hybrid vehicle. Such a vehicle battery may particularly benefit from the battery pack or the therrnal management system of the present disclosure as a vehicle battery is often subject to relatively rapid charging and discharging. Further, vehicles may be subject to great temperature differences and vehicle batteries may require both cooling and heating. BRIEF DESCRIPTION OF THE DRAWINGS The embodiments disclosed herein are illustrated by Way of example, and by not by Way of limitation, in the figures of the accompanying draWings. Like reference numerals refer to corresponding parts throughout the draWings, in Which Figure 1 is a schematic illustration of a battery pack 1 containing secondary cells 5 and a therrnal management system 10, Figure 2 shows a battery pack 1 and a part of a therrnal management system 10 that comprises a meandering temperature regulating conduit 12, wherein a cooling ﬂow direction 12c through the temperature regulating conduit 12 is illustrated, Figure 3 shows the upper half of the battery pack of figure 2 with a heating ﬂow direction 12h through the temperature regulating conduit 12 being illustrated, Figure 4 illustrates how the individual parameter of secondary cells may vary, and Figure 5 schematically illustrates a method 100 of arranging a plurality of secondary cells in a battery pack.

DETAILED DESCRIPTION Embodiments of the present disclosure will now be described more fully hereinafter. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those persons skilled in the art.

Figure 1 very schematically illustrates a battery pack 1. Battery packs 1 contain a plurality of secondary cells, such as typically ten to thirty secondary cells. In the schematic illustration of figure 1, only three secondary cells 5 are contained in the battery pack 1. There is shown a first secondary cell 5a, a second secondary cell 5b and a third secondary cell 5c.

Figure 1 further schematically illustrates a temperature regulating conduit 12 and a bidirectional ﬂow means 14 by means of which the secondary cells 5 may be selectively cooled or heated. There may also be provided a temperature regulating means (not shown), e. g. a heat pump, to provide for cooling and heating. The temperature regulating conduit 12, the bidirectional ﬂow means 14 and the temperature regulating means may form part of a therrnal management system The bidirectional ﬂow means 14 may be a bidirectional fan or pump. The temperature regulating conduit 12 may contain a temperature regulating ﬂuid such as a temperature regulating gas or a temperature regulating liquid, below referred to as a coolant.

Arrows in figure 1 illustrate a cooling flow direction 12c and an opposite heating ﬂow direction 12h. The bidirectional ﬂow means 14 may bring the coolant to selectively ﬂow through the temperature regulating conduit 12 in the cooling ﬂow direction 12c and in the heating ﬂow direction 12h, respectively. In figure 1, the temperature regulating conduit 12 is a closed circuit and may be referred to as a temperature regulating circuit.

Figure 2 shows an example of a battery pack 1 that contains 25 secondary cells 5. As in figure 1, a temperature regulating conduit 12 is provided to regulate the temperature of the secondary cells 5. In figure 2, a cooling ﬂow direction 12c illustrates the ﬂow of a coolant through the temperature regulating conduit 12 during cooling of the secondary cells 5. Figure 3 corresponds to figure 2, but with a heating ﬂow direction 12h illustrating the ﬂow of the coolant through during heating of the secondary cells 5. Temperature regulating means that may be included to provide for cooling and heating of the coolant are not shown in figures 2 or 3. The temperature regulating conduit 12 of figures 2 and 3 may be a temperature regulating circuit.

A plurality of battery packs 1 as illustrated in figures 1 to 3 may be electrically connected to each other and form a vehicle battery (not shown) for propelling a vehicle (not shown) such as a fully electrically propelled vehicle or a hybrid vehicle, such as a passenger car, a utility vehicle or an airplane.

Figure 4 illustrates how parameters of secondary cells may vary. Even though secondary cells are manufactured from the same materials and in the same process, when a plurality of such cells are examined after manufacture, their individual parameters typically follow a normal distribution around a mean value. In this context, the mean value may altematively be referred to as the designated value. For example, a parameter such as the intemal resistance Rim of a given plurality of secondary cells 5 may be distributed around a designated intemal resistance Rdes as shown in figure 4. The first secondary cell 5a has a higher intemal resistance than the second secondary cell 5b that in tum has a higher intemal resistance than the third secondary cell 5c. This may be expressed as Rum > Rguint > of Rami. Similarly, parameters such as the capacity C or the calendar loss Q10SS of a given plurality of secondary cells 5 may be distributed around respective mean values as illustrated in figure 4. The intemal resistance Rim is below referred to as R and the calendar loss Qioss is below referred to as Q.

The calendar loss Q may be deterrnined by electrically charging and discharging (subjecting to electrical loading) a newly manufactured secondary cell to measure its capacity. This cyclemay be repeated a few times. Next, the secondary cell is electrically charged again and stored for a period of time, such as 1-3 weeks. Finally, the capacity is again measured by discharging the secondary cell. The calendar loss Q may be calculated by comparing the capacity after storage to the capacity before storage.

The life length and the performance of secondary cells are affected by the operating temperature, e.g. the cell temperature during electrical charging or electrical discharging. Preferably, the secondary cells should be kept within a certain temperature range during operation. For example, the optimal operation temperature for a lithium-ion cell may be around degrees Celsius.

Secondary cells generally deteriorate faster when operating at temperatures higher than the optimal operation temperature, i.e. the cell service life may be reduced. In addition, the performance of the secondary cell may be reduced at a higher temperature. By performance may be meant the ability to absorb or provide electrical power.

Now, under the same conditions, a secondary cell of higher intemal resistance will operate at a higher temperature than a secondary cell of lower intemal resistance. For this reason, to optimise life and performance, a secondary cell of higher intemal resistance will require more efficient cooling than a secondary cell of lower intemal resistance.

As is illustrated in figures 1 to 3, the first, second and third secondary cells 5a, 5b, 5c are positioned along the temperature regulating conduit 12 based on their individual intemal resistance R. In view of the cooling ﬂow direction 12c, the first secondary cell 5a, which has the highest intemal resistance R among the three secondary cells, is positioned most upstream. Thus, the first secondary cell 5a will be most efficiently cooled since the temperature of the coolant is lower upstream.

In view of the cooling ﬂow direction 12c, the third secondary cell 5c is positioned most downstream as requires the less efficient cooling, as it has the lowest intemal resistance R. The second secondary cell 5b is positioned in-between the first and third secondary cells 5a, 5c along the temperature regulating conduit 12. Thus, in figures 1 to 3 the first, second and third secondary cells 5a, 5b, 5c are positioned in consecutive order of intemal resistance R along the temperature regulating conduit In view of the heating ﬂow direction 12h, the third secondary cell 5c, which has the lowest internal resistance R among the three secondary cells, is positioned most upstream. Thus, the third secondary cell 5c will be most efficiently heated since the temperature of the coolant is higher upstream. In view of the heating ﬂow direction 12h, the first secondary cell 5a is positioned most downstream as requires the less efficient heating, as it has the highest intemal resistance R. Again, the second secondary cell 5b is positioned in-between the first and third secondary cells 5a, 5c along the temperature regulating conduit Even though only three secondary cells 5a, 5b, 5c are referred to above, it is to be apprehended that each one of the secondary cells within the battery pack 1 may be positioned in consecutive order of intemal resistance R along the temperature regulating conduit 12. Thus, in the examples of figures 2 and 3, each one of the 25 secondary cells may be positioned in consecutive order of intemal resistance R along the temperature regulating conduit 12. The cell capacity C and the calendar loss Q may also be taken into account in such conscious positioning, as described below.

In some embodiments, for example to simplify the positioning, only some of the secondary cells within the battery pack 1 are consciously positioned based on individual intemal resistance R (and, optionally, based on capacity C and calendar loss Q). For example, only the secondary cells 5 that are located in the vicinity of the inlet or outlet of the temperature regulating conduit 12 within the battery pack 1, or only secondary cells 5 that deviate substantially from the designated intemal resistance value Rdes.

As a result of the deliberately chosen positioning of the secondary cells 5a, 5b, 5c, the differences in operating temperatures will be at least partially evened out during both cooling and heating. The more efficient cooling of the secondary cells that have a higher intemal resistance R will act to even out the operating temperature differences that would occur if the cooling of the secondary cells 5a, 5b, 5c would be equivalent, if the positioning was random, or if there would be no cooling at all. Additionally, the more efficient heating of the secondary cells that have a lower intemal resistance R will act to even out the operating temperature differences that would occur if the heating would be equivalent, or if there would be no heating at all. As is to be apprehended, the above-described positioning of the secondary cells is beneficial also when there are only provided means for cooling, or only means for heating of the battery pack.Practical trials have shown that the temperature difference between secondary cells may amount to up to 10 degrees Celsius owing to varying intemal resistance. The deliberately chosen positioning based on the intemal resistance signif1cantly decreases this temperature difference. Thereby, less energy needs be spent on therrnal management and/or the need for therrnal management (typically cooling) will be delayed during operation of the battery pack. A further advantage of a decreased temperature difference is that the state of power (SOP) of a battery is typically dependent on the temperature of the battery, and the secondary cell of the lowest temperature may dictate the state of power. Thus, a decreased temperature difference may lead to a higher and more accurate SOP.

It has been realised that it may be advantageous to base the positioning of the secondary cells along the temperature regulating conduit 12 not only on the individual resistance R but also on the individual capacity C. For example, if two secondary cells have the same, or nearly the same intemal resistance R, it may be advantageous to position the two secondary cells such that the one that has the lower capacity is more efficiently cooled.

In more detail, an individual cell therrnal rating TR of each secondary cell may be deterrnined and used for the positioning. The individual cell therrnal rating may be dependent on the individual intemal resistance R and on the individual capacity C.

The cell therrnal rating TR may be deterrnined in accordance with TR(R» C) : (X ' (Rdes _ R) + ß I (C _ Cdes) where ot is a weighting constant for the deviation of the intemal resistance R from a designated intemal resistance value Rdﬁs and ß is a weighting constant for the deviation of the capacity C from a designated capacity value Cdes.

As can be seen, a higher intemal resistance leads to a lower therrnal rating TR. A higher capacity leads to a higher therrnal rating TR.

It has further been realised that it may be advantageous to base the positioning of the secondary cells along the temperature regulating conduit 12 also on the individual calendar loss Q. For example, if two secondary cells have the same, or nearly the same intemal resistance R and capacity C, it may be advantageous to position the two secondary cells such that the one that has the higher calendar loss Q is more efficiently cooled. The secondary cell with the higher calendar loss Q is expected to exhibit a lower capacity after a period of use.Thus, the cell therrnal rating TR may altematively be deterrnined in accordance with TR(R»C»Q) I ala? _ Rint) + ß I (C _ Cdes) +YI (Qdes _ where y is a weighting constant for the deviation of the calendar loss Q from a designated (or mean) value Qdes. Thus, a higher individual calendar loss Q leads to a lower the therrnal rating TR.

Altematively, the cell therrnal rating TR may be deterrnined in accordance with C Q + y - Qdes TR(R,C,Q)=0(- +ß' Rdes Cdes It is to be appreciated that other forrnulas that take the intemal resistance R, the capacity C and/or the calendar loss Q into account may be used for consciously positioning the secondary cells 5 along the temperature regulating conduit 12. For example, the respective individual parameter values need not be compared to designated values but the absolute parameter values may be associated, e. g. multiplied, with their respective a weighting constants u, ß, y. Thus, the cell therrnal rating TR may yet altematively be deterrnined in accordance with TR(R,C,Q)=0(-R+ß'C+y'Q The weighting constants u, ß, y may be appropriately selected dependent on the intended application of the battery pack. For example, the weighting constant y may be higher for a battery pack to be used in a vehicle than for a battery back to be used in a frequently running machine.

The cooling or heating of the plurality of secondary cells 5 within the battery pack 1 may be accomplished by the temperature regulating conduit 12 extending adjacent to or through the battery pack 1. In the example of figure 1, an enclosure 2 of the battery pack 1 forms a section of the temperature regulating conduit 12. The enclosure 2 comprises a first and a second opening 3, 4 for the coolant to enter and exit the enclosure 2. In one embodiment (not shown), only involving cooling, a fan may be arranged to blow ambient air through the enclosure 2 via the first and a second openings 3, 4. In the example of figures 2 and 3, the temperature regulating conduit 12 is a pipe that extends through the enclosure 2 such that the coolant may ﬂow within the pipe through the enclosure 2. The pipe, or hose, enters and exists the enclosure 2 though a first and a second opening 3, 4. As is illustrated in figures 2 and 3, the temperatureregulating conduit 12 may meander through rows of secondary cells 5 arranged Within the enclosure Turning noW to figure 5, a method 100 of arranging a plurality of secondary cells 5 in a battery pack 1 Will be described. The method 100 is applicable to the above described battery packs 1, or to other battery packs holding a plurality of secondary cells, the temperature of Which may be regulated by a temperature regulating conduit The method 100 comprises providing 110 a plurality of secondary cells 5. The step of providing 110 the plurality of secondary cells 5 may involve manufacturing the secondary cells 5, or gathering available secondary cells The method 100 further comprises obtaining 120 at least one individual parameter of each secondary cell 5. Such a parameter may be the intemal resistance R as described above. Altematively, such parameters may be the intemal resistance R and the capacity C as described above. Altematively, such parameters may be the intemal resistance R, the capacity C and the calendar loss Q as described above. The step of obtaining 120 the at least one individual parameter may involve performing secondary cell 5 measurements to determine the respective parameter(s), or reading previously produced measurement data conceming each secondary cell 5. The previously produced measurement data may be printed on each secondary cell 5. Altematively, the measurement data may be stored in a database and the secondary cell 5 may be provided With a unique identification leading to the assigned measurement data. The step of obtaining 120 at least one individual parameter of each secondary cell 5 may comprise comprising obtaining 125, by calculation or by reading from the database, the individual cell therrnal rating TR described above.

The method 100 further comprises arranging the arranging 130 the plurality of secondary cells 5 in the battery pack 1. The step of arranging 130 the plurality of secondary cells 5 in the battery pack 1 comprises positioning at least some of the secondary cells 5 along the temperature regulating conduit 12 based on their individual intemal resistance R, as has been described above. As has also been described, the positioning may be based on the secondary cell individual intemal resistance R, capacity C and/or or calendar loss Q, for example on individual cell therrnal rating TR that in tum depends on intemal resistance R, capacity C and/or calendar loss.The document US20110213509A1 discloses attaching an identification designation to each of plural cells and plural blocks of cells included Within a large scale battery. Further, the document, see figure 7C and the description thereof, proposes taking the cell internal resistance into account When positioning pairs of cells in a block of cells. An expected temperature profile may be used to compute expected temperature differences between the blocks, and a block capacity may be selected in view of the expected block temperature differences. Notably, document US20110213509A1 is not related to temperature regulation.

In the present disclosure, the intemal resistance of secondary cells is referred to. In most applications, the secondary cells 5 of a battery pack 1 as herein described is subject to DC (direct current) load. As is known to a skilled person, under DC load the intemal resistance equals the intemal impedance. However, for the sake of completeness, in the present disclosure reference could be made to "intemal resistance or intemal impedance".

Modifications and other variants of the described embodiments Will come to mind to ones skilled in the art having benefit of the teachings presented in the foregoing description and associated draWings. Therefore, it is to be understood that the embodiments are not limited to the speciﬁc example embodiments described in this disclosure and that modifications and other variants are intended to be included Within the scope of this disclosure.

For example, the secondary cells may be affected by their temperature not only during operation (charging/discharging). The conscious positioning of the secondary cells along the temperature regulating conduit described herein may be advantageous also should the temperature of the secondary cells be regulated during idle conditions. An idle condition may correspond to a battery pack being stored Without operation, a vehicle battery may for example be located in a parked vehicle that is exposed to hot or cold climate. In one conceivable embodiment, the positioning (and the therrnal rating, if used for the positioning) is based only on the calendar loss Q.

Furthermore, although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Therefore, persons skilled in the art Would recognize numerous variations to the described embodiments that Would still fall Within the scope of the appended claims. As used herein, the terms "comprise/comprises" or "include/includes" do not exclude the presence of other elements or steps. Furthermore, although individual features may be included in different claims (or embodiments), these may possibly advantageously be combined, and the inclusion of different clainis (or enibodinients) does not iniply that a certain combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Finally, reference nunierals in the clainis are provided nierely as a clarifying example and should not be construed as liniiting the scope of the clainis in any Way.

Claims

1.A method (100) of arranging a plurality of secondary cells (5) in a battery pack (1), Wherein the battery pack (1) is configured such that the temperature of said plurality of secondary cells (5) may be regulated by a temperature regulating conduit (12), the method (100) comprising - providing (110) a plurality of secondary cells (5), characterized by the method comprising: - obtaining (120) at least one individual parameter of each secondary cell (5), the individual parameter comprising the individual intemal resistance (R), and - arranging (130) the plurality of secondary cells (5) in the battery pack (1), Wherein arranging (130) the plurality of secondary cells (5) in the battery pack (1) comprises positioning at least some of the secondary cells (5) along the temperature regulating conduit (12) based on their individual intemal resistance (R). The method of claim 1, Wherein the plurality of secondary cells (5) comprise a first secondary cell (5a), a second secondary cell (5b) and a third secondary cell (5c), Wherein the first secondary cell (5 a) has a higher intemal resistance (R) than the second secondary cell (5b) that has a higher intemal resistance (R) than the third secondary cell (5 c), and Wherein the first, second and third secondary cells (5a, 5b, 5c) are positioned in order of intemal resistance (R) along the temperature regulating conduit (12). The method of claim 1 or 2, the individual parameter comprising the individual capacity (C) and Wherein the positioning is based on the individual intemal resistance (R) and on the individual capacity (C) of the secondary cells (5). The method of any preceding claim, the individual parameter comprising the individual calendar loss (Q) and Wherein the positioning is based on the individual intemal resistance (R) and on the individual capacity (C) and/or on the individual calendar loss (Q) of the secondary cells (5). The method of claim 3 or 4, wherein the individual parameters (R, C, Q) are given different weights for the positioning. The method of any of claims 3 to 5 comprising obtaining (125) an individual cell therrnal rating (TR) of each secondary cell (5), wherein the individual cell therrnal rating (TR) is dependent on the individual intemal resistance (R) and on the individual capacity (C) and/or on the individual calendar loss (Q) of the secondary cells (5). The method of claim 6, wherein obtaining (125) the individual cell therrnal rating (TR) comprises associating the respective individual parameters (R, C, Q) with a respective weighting constant (ot, ß, y). The method of claims 6 or 7, wherein the plurality of secondary cells (5) comprise a first secondary cell (5a), a second secondary cell (5b) and a third secondary cell (5c), wherein the first secondary cell (5a) has a lower therrnal rating (TR) than the second secondary cell (5b) that has a lower therrnal rating (TR) than the third secondary cell (5c), and wherein the first secondary cell (5a) is positioned upstream relative to the second secondary cell (5b) that is positioned upstream relative to the third secondary cell (5c), as seen in a cooling ﬂow direction (12c) of the temperature regulating conduit (12). The method of claim 8, wherein the first secondary cell (5 a) is positioned downstream relative to the secondary cell (5b) that is positioned downstream relative to the third secondary cell (5c), as seen in a heating ﬂow direction (12h) of the temperature regulating conduit (12). A battery pack (1) comprising a plurality of secondary cells (5), wherein - the battery pack (1) is configured such that the temperature of said plurality of secondary cells (5) may be regulated by a temperature regulating conduit (12) and characterised by: - at least some of the secondary cells (5) are positioned along the temperature regulating conduit (12) based on their individual intemal resistance (R). The battery pack (1) of claim 10, wherein the plurality of secondary cells (5) comprise a first secondary cell (5a), a second secondary cell (5b) and a third secondary cell (5c), wherein the first secondary cell (5 a) has a higher internal resistance (R) than the second secondary cell (5b) that has a higher internal resistance (R) than the third secondary cell (5 c), and wherein the first, second and third second secondary cells (5 a, 5b, 5c) are positioned in order of internal resistance (R) along the temperature regulating conduit (12). The battery pack (1) of claim 11, wherein the first secondary cell (5a) is positioned upstream relative to the second secondary cell (5b) as seen in a cooling ﬂow direction (12c) of the temperature regulating conduit (12) and wherein the first secondary cell (5a) is positioned downstream relative to the second secondary cell (5b) as seen in a heating ﬂow direction (12h) of the temperature regulating conduit (12). A thermal management system (10) characterized by: a battery pack (1) according to any one of claims 10 to 12, a temperature regulating conduit (12), wherein the battery pack (1) is configured such that the temperature of the plurality of secondary cells (5) within the battery pack (1) may be regulated by the temperature regulating conduit (12), and a bidirectional ﬂow means (14) for obtaining a cooling flow in a cooling flow direction (12c) through the temperature regulating conduit (12) and a heating flow in a heating flow direction (12h) through the temperature regulating conduit (12), wherein the heating flow direction (12h) is opposite to the cooling flow direction (12c). The therrnal management system of claim 13, wherein the bidirectional flow means (14) is apump. A vehicle battery for propelling a vehicle, wherein the vehicle battery comprises a battery pack (1) according of any one of claims 10 to 12 and/or a thermal management system (10) according to claim 13 or 19