WO2017220975A1

WO2017220975A1 - Battery pack

Info

Publication number: WO2017220975A1
Application number: PCT/GB2017/051769
Authority: WO
Inventors: Roger Wise
Original assignee: Koolkwic Limited
Priority date: 2016-06-23
Filing date: 2017-06-16
Publication date: 2017-12-28
Also published as: GB201610975D0

Abstract

A battery unit comprising at least one battery cell, and a Peltier module thermally coupled to at least one graphite sheet or ribbon. [Figure 2]

Description

BATTERY PACK

This invention relates generally to a battery module for a battery pack and, more particularly but not necessarily exclusively, to a battery module for a battery pack for use in a hybrid vehicle or a solely electric vehicle or the like. The invention also relates to a battery pack comprising a plurality of such battery modules and a thermal management system for such a battery pack.

In recent years, due to increasing focus on environmental protection issues, hybrid vehicles, having relatively very low C0₂ emissions, and electric vehicles which do not emit C0₂, have become increasingly prevalent. In order to supply power to the driving motor and other electrical systems within the vehicle, a battery pack is mounted therein.

Such battery packs generally comprise an array of battery modules mounted on a tray and encased within a housing, which tends to be mounted in a lower part of the vehicle. Each battery module comprises a plurality of battery cells, electrically connected together.

Lithium-ion (Li-ion) battery cells are currently considered to be advantageous for use in electric vehicles as they can generate twice the power of their nickel-metal-hydride (NiMH) counterparts, which means that the array of battery cells can be lighter and still give the vehicle a driving range comparable to that of one driven by a conventional internal combustion engine. Other advantages of Li-ion batteries include the fact that they have a relatively low self-discharge rate, which means that they do not lose a lot of power if a vehicle is not driven for a period of time.

However, batteries such as Li-ion batteries, used for this purpose, need to be maintained at an optimum working temperature in order to ensure optimum performance in use. Thus, temperature control mechanisms in the form of thermal management systems are employed, wherein liquid is pumped or otherwise caused to flow around the battery modules, the temperature of which liquid is controlled in order to attempt to maintain an optimum working temperature of the battery cells. Such thermal management systems tend not to be very efficient, partly because the same body of liquid is used to control the temperature of all of the individual battery modules. Thus, heat from one or more modules along the fluid flow path is transferred to the liquid, which then needs to be further cooled for battery modules further down the fluid flow path. This is clearly inefficient. Furthermore, the use of liquid as a cooling/heating fluid adds to the weight of the overall structure, which is clearly

undesirable, and the rate at which liquid can change its temperature as required by the thermal management system is also relatively slow and increases the inefficiency of the overall system.

Still further, the structure of known battery packs and configuration of known thermal management systems do not allow for efficient or accurate thermal management of individual cells or modules. As a result, problems can arise with battery cells or packs being at different temperatures (whereas they are being thermally managed by the same body of fluid having a substantially uniform temperature), such that optimum working temperature and, therefore, performance, cannot be effectively achieved. Furthermore, the life of the battery pack is limited to the longevity of a single battery module, which can be severely compromised if one or more of the battery modules is routinely or consistently operating at a non-optimum temperature.

Aspects of the present invention seek to address at least some of these issues and provide an improved battery module, battery pack arrangement and thermal management system in which at least some of the above-mentioned problems are ameliorated. Exemplary embodiments of the present invention seek to provide a battery pack that is significantly lighter in weight than currently comparably sized battery packs; exemplary embodiments further seek to provide a battery module and/or battery pack comprising a structure and using materials that enable the efficiency of the cooling/heating of battery cells to occur more responsively, thereby significantly increasing the resultant efficiency in relation to known arrangements. In some exemplary embodiments, the structure and materials used enable a thermal management system to be used that does not require a separate flow of

cooling/heating fluid at all, thereby further reducing the weight of the system and increasing efficiency. The structure of the battery modules and resultant battery pack according to at least some exemplary embodiments, enables each battery cell (or group of physically proximate cells) to be monitored and managed individually so that the longevity of the battery cells and, therefore, the battery packs can be increased by a significant percentage relative to known battery packs.

Thus, in accordance with a first aspect of the present invention, there is provided a battery unit comprising at least one battery cell thermally coupled to at least one graphite sheet or ribbon.

The graphite sheet or ribbon may be formed of high grade graphite, at least 75% Cg, or even at least 85% Cg. In an exemplary embodiment, the thickness of said graphite sheet or ribbon is ΙΟμιη or less, or even 5μιη or less.

The graphite sheet or ribbon may be thermally coupled at one end to said battery cell and at the other end to a heat sink located remotely from said battery cell. In an exemplary embodiment, the battery cell may be in the form of a pouch, indeed in an exemplary embodiment, the battery cell may be a Lithium-ion or Lithium-air cell.

A battery unit according to an exemplary embodiment of the invention may comprise a battery cell, a thermally conductive plate, and a Peltier module, wherein said battery cell has first and second opposing faces and said thermally conductive plate is abutted against a first face of said battery cell, said Peltier module comprises a thermoelectric device having first and second opposing active sides, a first of said active sides being thermally coupled to said thermally conductive plate and the other of said active sides being thermally coupled to said graphite sheet or ribbon.

Optionally, the thermoelectric device may be mounted within an aperture in a mounting block with said first and second active sides exposed.

The mounting block may be formed of a thermally insulative material, such as plastic or polymer.

Optionally, the battery unit may further comprise a sensor or other means for sensing the temperature of said battery cell and generating data representative thereof. According to another aspect of the present invention, there is provided a battery assembly comprising a battery unit substantially as described above and a thermal management system, said thermal management system being configured to receive data representative of a temperature of said battery cell, determine if said temperature of said battery cell is within a predetermined range and, if not, generate one or more control signals configured to alter an operational status of said thermoelectric device so as to increase or decrease the heat of said first active side thereof, as required.

In accordance with yet another aspect of the present invention, there is provided a battery module comprising at least two battery units substantially as described above, mounted side-by- side with a battery cell of a first battery unit being located adjacent a battery cell of a second battery unit, with a thermal barrier plate therebetween. In accordance with a further aspect of the present invention, there is provided a battery pack comprising an array of battery modules substantially as described above.

In another exemplary embodiment of a battery unit according to the first aspect of the invention, a graphite ribbon may be thermally coupled at one end to an outer surface of said battery cell and thermally coupled at the other end to a thermoelectric device.

In one exemplary embodiment, each of a plurality of graphite ribbons may be thermally coupled at one end to an outer surface of said battery cell and thermally coupled at the other end to a thermoelectric device. The thermoelectric device may be provided in a thermal management system located remote from said battery unit.

The thermal management system may be configured to receive data representative of a temperature of said battery cell, determine if said temperature of said battery cell is within a predetermined range and, if not, generate one or more control signals configured to alter an operational status of said thermoelectric device so as to increase or decrease the heat of said first active side thereof, as required.

In accordance with yet another aspect of the present invention, there is provided a battery pack comprising an array of battery cells, wherein adjacent battery cells are separated by a respective thermal barrier plate, each said battery cell being thermally coupled to a graphite ribbon at one end, the other end of said graphite ribbon being thermally coupled to a thermoelectric device located remotely from said battery pack.

The thermoelectric device may be provided in a thermal management system located remote from said battery pack, and the thermal management system may be configured to receive data representative of a temperature of said battery cell, determine if said temperature of said battery cell is within a predetermined range and, if not, generate one or more control signals configured to alter an operational status of said thermoelectric device so as to increase or decrease the heat of said first active side thereof, as required.

Once again, each of a plurality of graphite ribbons may be thermally coupled at one end to an outer surface of each said battery cell and thermally coupled at the other end to a thermoelectric device.

The advantages of thermoelectric or Peltier technology are many: solid state, light in weight, very reliable and the ability to cool down under ambient temperature and/or target generated heat. Such devices lend themselves well to targeted cooling or heating applications in confined spaces. However, in current applications, Peltier technology has some significant disadvantages, including high power consumption and inefficiency, having a poor coefficient of power. In accordance with exemplary embodiments of the present invention, high tech materials (such as high grade graphite or annealed pyrolytic graphite materials) and novel thermal management techniques are employed to address the above-mentioned problems, providing arrangements in which one or more of the advantages listed below can be achieved:

• No moving parts, pumps or radiators are required: all waste heat is dissipated naturally; thereby providing a light weight construction wherein the Lithium pouches can, for example, be mounted in plastic or polymer.

• The Lithium pouches can be predictably managed using, for example, GPS technology, tracing the topography of the highway, whereas prior art thermal management systems cannot incorporate such functionality.

• With reference to the point above, the use of such GPS technology in this application might be particularly advantageous for motor sport as the GPS could be used to predict where the demands from the circuit occur and cool the battery cells accordingly, thereby giving the batteries extended charge due to finite management.

• The battery pouch arrangement is entirely scalable according to application and requirements specifications.

• No liquid cooling is required. Thus, the system is significantly safer than

known systems as, in the event of an accident, there is no danger of high voltage DC being exposed to liquid. Furthermore, the system can be made highly responsive to any temperature change required. Thus, in the event that the battery pack is determined not to be at its optimum temperature (say, at start up), this can be rectified substantially immediately.

• The thermal management system could take advantage of thermal heat

recovery from other parts of the vehicle, for example the brakes, to put a spike of energy into the Peltier circuit (i.e. heat from the brakes can be converted to a spike of electrical energy which is then fed to the Peltier circuit), which would be particularly useful for stop-go public transport systems and motor sport, for example. • A vehicle employing a battery pack and thermal management system according to an exemplary embodiment of the present invention could be exported anywhere in the world and any climate because no matter how extreme the ambient temperature is (high or low), the thermal management system can be configured to heat or cool the Lithium pouches as required, to maintain the optimum working temperature.

These and other aspects of the invention will be apparent from the following specific description in which embodiments of the present invention are described, by way of examples only, and with reference to the accompanying drawings, in which: Figure 1 is a schematic cross-sectional side view of a battery module according to a first exemplary embodiment of the present invention;

Figure 2 is a schematic cross-sectional side view of a battery pack according to a first exemplary embodiment of the present invention;

Figure 3 is a schematic cross-sectional side view of a battery pack according to a second exemplary embodiment of the present invention; and

Figure 4 is a schematic front view illustrating the configuration of a single battery cell of the battery pack of Figure 3.

Referring to Figure 1 of the drawings, a battery module 12 according to an exemplary embodiment of the present invention comprises a Lithium-ion (or Lithium-air) battery cell 14 or 'pouch' having first and second opposing faces 14a, 14b. Lithium cells must be maintained in a stable condition under different driving demands (Duty Cycles) and different ambient temperatures. In contrast to prior art arrangements, methods/arrangements according to exemplary embodiments of the present invention provide accurate thermal management of each pouch. A thermally conductive heating/cooling plate 18, having first and second opposing faces 18a, 18b, is provided with its first face 18a abutted against the first face 14a of the battery cell 14. The thermally conductive plate 18 may, for example, comprise alloy or graphite sheet material, but other, lightweight heat conductive sheet materials suitable for this purpose (i.e. transferring heat to and from the respective battery cell 14) will be apparent to a person skilled in the art, and the present invention is not necessarily intended to be limited in this regard.

A Peltier module 20 comprises a thermally insulative mounting block 22 having a thermoelectric or Peltier device 24 mounted through an aperture therein. Thus, the thermoelectric or Peltier device 24 is surrounded at its side edges with the insulative material of the mounting block 22, leaving outer faces of respective plates thereof exposed and their planes substantially flush with the plane of the respective face of the mounting block 22. Thus, an outer face 24a of one of its plate is exposed on one side of the mounting block and substantially flush with the planar face of the mounting block on that side, and an outer face 24b of its plate is exposed in a similar manner at the opposing plane of the mounting block 22. One of the outer faces 24a of the Peltier device and the corresponding respective face of the mounting block 22 is abutted against the second face 18b of the heating/cooling plate 18. The other outer face 24b of the Peltier device 24 and corresponding respective face of the mounting block 22 is abutted against a high grade graphite sheet or ribbon 26. Reference to high grade graphite, as will be well known to a person skilled in the art, is intended to be a references to its purity. Grading of graphite is based on its percentage of carbon in graphite form. Flake graphite grades at 2 - 12% Cg and amorphous graphite grades at 12-17% Cg, whereas lump graphite is known to grade at least 89% Cg and sometimes up to 99% Cg (i.e. almost pure graphite). The higher the grade of graphite used, the thinner the graphite sheet/ribbon can be in order to achieve the desired heat transfer properties. In this case, the graphite sheet/ribbon 26 may be of grade 80 - 99.9% Cg and, therefore, around 4μιη thick, but the present invention is not necessarily intended to be limited in this regard, and it will be appreciated by a person skilled in the art that the grade and, therefore the thickness of the graphite sheet/ribbon can be altered to suit specific requirements and availability, as well as cost/weight issues. Indeed, the term "graphite" used herein may refer to any form of graphite in ribbon or sheet form and/or annealed pyrolytic graphite material, and the present invention is not necessarily intended to be limited in this regard.

The high grade graphite sheet/ribbon 26 extends from the battery module 12 to, for example, a separate heat sink or even the vehicle chassis to allow heat carried thereby (away from the battery module) to be dissipated (or, indeed, recovered elsewhere). High grade graphite sheet/ribbon material can transfer heat significantly faster (e.g. around 10-12 times faster) than, for example, aluminium. Thus, heat transferred thereto from the adjacent Peltier plate is very quickly conducted away from the battery module. For this reason, the material of which the mounting blocks 22 are made does not need to be highly heat resistant, as there is little opportunity for heat to build up in the mounting block and cause damage thereto. Thus, in an exemplary embodiment of the present invention, the mounting block 22 can be made of a very lightweight thermally insulative material, such as plastic, polymer or the like and the overall weight of the module, as well as its thermal efficiency, can be optimised.

Another significant advantage afforded by the use of high grade graphite sheet/ribbon is that it eliminates the need to provide a separate flow of cooling fluid as part of a thermal management system: excess heat is, instead, very quickly and safely conducted out of the battery module and to another part of the vehicle by the high grade graphite sheet/ribbon 26. The general structure of a thermoelectric or Peltier device 24 will be well known to a person skilled in the art and will not be discussed in detail here. Suffice it to say that, by the application of a current to the device, its plate can be made to have a hot side and a cold side, and which face of the plate is hot and which is cold at any one time is dependent on the polarity of the applied current. Thus, the outer face 24a (against the heating/cooling plate 18) can be made selectively hot or cold, depending on whether it is required to heat or cool the battery cell 14, by selecting the correct polarity of current applied thereto. Therefore, a targeted thermal management system can be provided in respect of a single battery cell 14, because heating and cooling can be selectively applied thereto. One or more sensors (not shown) may, therefore, be provided within the battery module 12, for measuring the temperature thereof (with a view to identifying "hotspots" for example), and transmitting temperature measurement data to a thermal management system (not shown), which will be described in more detail later. The thermal management system is configured to monitor the temperature of an individual battery module 12 and generate control signals configured to control the size and polarity of current applied to the Peltier device associated therewith. Referring now to Figure 2 of the drawings, a battery pack according to an exemplary embodiment of the present invention comprises a plurality of battery modules 12, of the type described above with reference to Figure 1, arranged in 'back to back' relation along a length thereof. Thus, the battery pack 10 can be considered in 'sections' of two battery modules 12, one on each side of the high grade graphite sheet/ribbon 26, 'sandwiched' between a pair of separator plates 16. The separator plate 16 is intended to act as a thermal barrier between the battery cells 14 and the ends of the battery pack section and respective battery cells of adjacent sections. Thus, a separator plate 16 is abutted against the respective second face 14b of each battery cell 14 in a 'section' . The separator plates 16 can be made of any suitable, lightweight material (to resist heat transfer between immediately adjacent battery cells). For example, each separator plate 16 may comprise a sheet of alloy material or aluminium having a thermal barrier coating. However, other suitable sheet materials (and/or coatings) for providing thermal barrier separator plates 16 for this purpose will be apparent to a person skilled in the art and the present invention is not necessarily intended to be in any way limited in this regard.

Thus, a battery pack 10 according to an exemplary embodiment of the present invention comprises a plurality of the above-mentioned battery pack 'sections' (each comprising two adjacent, 'back to back' battery modules 12 of the type described above in relation to Figure 1 of the drawings), with the 'sections' being arranged in side-by-side relation along a length thereof. The number of sections required for a battery pack will be entirely dependent on the application for which it is required, and the present invention is not intended to be in any way limited in this regard. To summarise the repeatable structure of the battery pack according to this exemplary embodiment of the present invention, it comprises (with each element being abutted against the next):

• Separator plate 16;

• Battery cell 14;

• Heating/cooling plate 18;

· Peltier device 24 mounted in mounting block 22;

• High grade graphite sheet/ribbon 26;

• Peltier device 24 mounted in mounting block;

• Heating/cooling plate 18;

• Battery cell 14;

· Separator plate 16;

• Battery cell 14;

• Heating/cooling plate 18;

• Peltier device 24 mounted in mounting block 22;

• and so on to achieve the size of battery pack required. Overall, the structure of the battery pack and the materials used enables the provision of a highly compact, lightweight and thermally efficient component. The modular structure of the battery pack provides highly flexible design options and, additionally, the ability to provide a targeted thermal management system that enables the working temperature of each individual battery module to be monitored and controlled to maintain its respective optimum working temperature. It has been established by the inventors that maintaining each Lithium pouch within the manufacturer's optimum working temperature, the reliability of the pouch is dramatically increased, with a corresponding decreased impact on warranty claims as well as extended vehicle range by retaining its charge.

Thus, and as mentioned above, a control system (not shown) may be provided, that comprises the above-mentioned sensors associated with respective battery cells, and a control unit configured to receive measurement data from the sensors and generate control data for controlling respective current flow to the thermoelectric or Peltier devices 24 to control the polarity of each device (i.e. which side is hot and which is cold) and the degree of

heating/cooling provided by the respective sides of a device. A busbar (not shown), or similar arrangement, may be provided along the base of the battery pack 10, with current feeds to each of the thermoelectric or Peltier devices. As explained above, each Peltier device 24 has an exposed first face 24a (on one side of the respective mounting block 22) that abuts a respective heating/cooling plate 18 (for transferring heat to an from the respective battery cell 14), and a second exposed face 24b (on the other side of the respective mounting block 22) that abuts the a high grade graphite sheet/ribbon 26. In use, and in respect of each battery cell 14, the control unit will receive temperature measurement data from a respective sensor associated with the cell and compare the measurement data with some predetermined level or range defined as the optimum working temperature for the cell. If a discrepancy is identified, control signals are generated to cause a remedying action to be taken. Thus, if it is determined that a battery cell is operating at a temperature that is deemed too high, the resultant control signal(s) will be configured to increase/decrease the current applied to the respective Peltier device and/or reverse its polarity, with the ultimate goal of reducing the temperature of the side 24a of the Peltier device abutting the respective heating/cooling plate 18 and, consequently, increasing the temperature of the side 24b abutting the adjacent high grade graphite sheet/ribbon 26. The heating/cooling plate 18 will thus be cooled, and excess heat will be quickly conducted out of the battery pack via the graphite sheet/ribbon 26.

Conversely, if it is determined that a battery cell is operating at a temperature that is deemed to be too low, the resultant control signal(s) will be configured to increase/decrease the current applied to the respective Peltier device and/or reverse its polarity, with the ultimate goal of increasing the temperature of the side 24a of the Peltier device abutting the respective heating/cooling plate 18 and, consequently, decreasing the temperature of the side 24b abutting the adjacent high grade graphite sheet/ribbon 26. The heating/cooling plate 18 will thus be heated and the heat transferred to the battery cell.

It will be appreciated that each Peltier module may, in fact, comprise more than one Peltier device. Indeed, for example, a pair of Peltier devices, one for heating and one for cooling, could be included in each Peltier module.

Referring now to Figure 3 of the drawings, in an alternative exemplary embodiment of the present invention, a battery pack 100 comprises an array of closely spaced battery cells 140, separated only by respective thermal barrier plates 160. Once again, the separator plates 160 can be made of any suitable, lightweight material (to resist heat transfer between immediately adjacent battery cells). For example, each separator plate 160 may comprise a sheet of alloy material or aluminium having a thermal barrier coating. However, other suitable sheet materials (and/or coatings) for providing thermal barrier separator plates 160 for this purpose will be apparent to a person skilled in the art and the present invention is not necessarily intended to be in any way limited in this regard.

The battery cells 140 may, once again, be Lithium- ion or Lithium-air 'pouches', but the present invention is not necessarily intended to be limited in this regard. Each battery cell 140 has attached thereto a set of high grade graphite ribbons 260, and each set of graphite ribbons 260 extend, from a respective battery cell, out of the battery pack 100 itself to a thermal management system 250 at another location within the vehicle, remote from, the battery pack. In an exemplary embodiment, the battery pack and the thermal management system may be housed in close proximity, possibly in the form of an integrated battery unit. However, it will be apparent that, in this case, that is not essential and the thermal

management system could be located in a different part of the vehicle altogether, if required by the application. Once again, one or more temperature sensors (not shown) is provided in respect of each battery cell 140 and configured to transmit temperature measurement data to the thermal management system, wirelessly or otherwise.

More specifically, and referring to Figure 4 of the drawings, in this exemplary embodiment, each battery cell 140 or 'pouch' has affixed thereto a set of four graphite ribbons 260. An end of a first graphite ribbon 260a is affixed to the outer cover of the pouch at or near the positive terminal of the battery cell; an end of a second graphite ribbon 260b is affixed to the outer cover of the pouch at or near the negative terminal of the battery cell; the ends of third and fourth graphite ribbons 260c, 260d are affixed to the outer cover and extend along a substantial portion of the longitudinal height of the pouch from a location at or near a lower edge thereof to the opposing upper edge, between the terminals. The third and fourth graphite ribbons 260c, 260d are, in this exemplary embodiment, held in close contact with the outer cover of the pouch along substantially the whole length between the above-mentioned location at or near the lower edge and the opposing upper edge by, for example, heat resistant adhesive or other suitable fixing means.

The opposing ends of the graphite ribbons 260a-d terminate at thermocouples 261 within a thermal management system control unit 250. Each thermocouple 261 is configured to thermally couple a respective end of a graphite ribbon to a side or plate of a respective thermoelectric or Peltier device housed within the unit 250. Thus, the thermal management system, in this case, comprises an array of four thermoelectric or Peltier devices 240 for each battery cell 140. The control unit 250 is further provided with a sheet 255 of high grade graphite, thermally coupled to the thermoelectric or Peltier devices 24, to act as an efficient and high speed heat sink therefor. It is envisaged, that each graphite ribbon could, in fact, be thermally coupled to more than one Peltier device in the thermal management system control unit. For example, each graphite ribbon may be thermally coupled to a pair of Peltier devices, one for heating and one for cooling as required.

Thus, in this case, the battery pack it self can be made significantly smaller and lighter again, with all thermal management elements being housed remote therefrom. The use of high grade graphite ribbon in this case, enables heat to be transferred quickly and efficiently to and from the battery cells 140, as required, thereby enabling the battery pack housing and any peripheral components and elements thereof to be made of lightweight and thin materials, as they are not required to withstand high levels of heat. Indeed, purely by way of example, in a prior art battery pack, 192 battery cells (pouches) are provided at a weight of 300kg, whereas a battery pack according to an exemplary embodiment of the present invention including 192 cells (pouches) would weigh just 220kg. Also housed within the thermal management system control unit 250 or, alternatively, nearby, there is a busbar or similar arrangement and a plurality of feeds, one for each thermoelectric or Peltier device 240, configured to apply current thereto in accordance with control signals generated by the thermal management system. As before, in use, and in respect of each battery cell 140, the control unit will receive temperature measurement data from a respective sensor associated with the cell and compare the measurement data with some predetermined level or range defined as the optimum working temperature for the cell. If a discrepancy is identified, control signals are generated to cause a remedying action to be taken. Thus, if it is determined that a battery cell is operating at a temperature that is deemed too high, the resultant control signal(s) will be configured to increase/decrease the current applied to the respective Peltier devices and/or reverse their polarity, with the ultimate goal of reducing the temperature of the side of the Peltier devices coupled to the graphite ribbons 260 attached to that particular cell.

Conversely, if it is determined that a battery cell is operating at a temperature that is deemed to be too low, the resultant control signal(s) will be configured to increase/decrease the current applied to the respective Peltier device and/or reverse its polarity, with the ultimate goal of increasing the temperature of the sides of the Peltier devices coupled to the graphite ribbons 260 for that particular cell. In an alternative exemplary embodiment, instead of using sensors in or on the battery cells themselves to trigger thermal management, the thermal status of the graphite ribbons 260 can be used for this purpose. Thus, when a section of a battery cell 140 heats up on demand/Duty Cycle, the heat will travel up the respective ribbon into the control unit 250, and this would trigger the respective thermocouple to 'ask' the respective Peltier device 240 for heating or cooling. The control unit 250 would be configured to apply the required level/polarity of current to the Peltier device to meet the requirement and the resultant heating/cooling would be sent back down the same graphite ribbon to manage the cell. In some exemplary embodiments, where 'hot spots' are known to occur in the same place in each battery cell of an array, a single Peltier device 240 could be provided to service all of the modules in the battery pack. In the example shown, four graphite ribbons are arranged on the outer cover of each battery cell 140, with the aim of ensuring that heating/cooling thereof is substantially uniform across its surface area. However, in an alternative embodiment, a heating/cooling plate may be affixed over a surface of the outer cover of the battery cell, for dispersed thermal transfer, such that only a single ribbon or sheet is required, coupled to a single thermoelectric or Peltier device, to heat/cool each cell.

Thus, the battery pack and/or battery unit according to various aspects of the present invention facilitate a thermal management system that can be used to target individual cells with either heating or cooling to maintain their temperature within the specified range, optimising efficiency and improving performance and useful life. The targeted cooling or heating can be delivered as soon as increases or decreases in temperature are sensed, by using automated control systems, and cells can thus be kept within the specified temperature range, rather than having to be cooled or heated once their temperature has gone beyond the boundaries of the range specified. Heating/cooling can also be targeted to specific areas, e.g. a 'weak' or 'failing' cell.

An additional significant benefit of the battery pack and/or battery unit according to various aspects of the present invention is that there is no need for liquid cooling and, instead, a zero thermal runaway solid state thermal management system is facilitated where no liquids need to be present such that, and unlike liquid cooled systems, in the event of a collision, for example, there is no danger of any combustibility through high voltages being combined with liquids.

It will be apparent to a person skilled in the art, from the foregoing description, that modifications and variations can be made to the described embodiments without departing from the scope of the invention as defined by the appended claims. It is particularly important to note that, contrary to conventional liquid cooling systems, the present invention facilitates highly responsive control of the battery working temperature, and can be used to ensure that a battery pack is always and substantially immediately at its optimum working temperature upon start-up for example, or in response to a sudden climatic change.

Furthermore, in all cases, an automatic control function may be provided within the thermal management system, configured to control the temperature of the individual battery cells on the basis of prediction signals. For example, the automatic temperature control function may receive as an input, signals from a GPS or similar positioning system, such input signals being representative of the topography of the environment along the path followed by the vehicle. Thus, the ongoing load on the battery modules can be predicted: for example, if the vehicle needs to travel uphill, the load on the battery cells will increase and, therefore the temperature will also increase. This increase in temperature can thus be predicted and the thermal management of the battery pack controlled accordingly. Similarly, some satellite navigation systems can provide an indication of traffic congestion and other situations that may affect the thermal management of the battery cells, and the automatic temperature control function may be configured to receive and utilise such signals in order to effect predictive thermal management of the battery pack. In other exemplary embodiments, the automatic control function may be configured to be pre-programmed for a particular route or environment. In one example, the route may comprise a motor racing circuit or the like, whereby a thermal management schedule can be pre-programmed and executed as the vehicle moves around the route.

Claims

1. A battery unit comprising at least one battery cell, and a Peltier module thermally coupled to at least one graphite sheet or ribbon.

2. A battery unit according to claim 1, wherein said graphite sheet or ribbon

comprises annealed pyrolytic graphite material.

3. A battery unit according to claim 1, wherein said graphite sheet or ribbon is

formed of high grade graphite, at least 75% Cg.

4. A battery unit according to claim 3, wherein said graphite sheet or ribbon is

formed of high grade graphite, at least 85% Cg.

5. A battery unit according to any of the preceding claims, wherein the thickness of said graphite sheet or ribbon is ΙΟμιη or less.

6. A battery unit according to claim 5, wherein the thickness of said graphite sheet or ribbon is 5μιη or less.

7. A battery unit according to any of the preceding claims, wherein said graphite sheet or ribbon is thermally coupled at one end to said battery cell and at the other end to a heat sink located remotely from said battery cell.

8. A battery unit according to any of the preceding claims, wherein said battery cell is in the form of a pouch.

9. A battery unit according to claim 8, wherein said battery cell is a Lithium- ion or Lithium- air cell.

10. A battery unit according to any of the preceding claims, comprising a battery cell, a thermally conductive plate, and a Peltier module, wherein said battery cell has first and second opposing faces and said thermally conductive plate is abutted against a first face of said battery cell, said Peltier module comprises a

thermoelectric device having first and second opposing active sides, a first of said active sides being thermally coupled to said thermally conductive plate and the other of said active sides being thermally coupled to a graphite ribbon.

11. A battery unit according to claim 10, wherein said thermoelectric device is

mounted within an aperture in a mounting block with said first and second active sides exposed.

12. A battery unit according to claim 11, wherein said mounting block is formed of thermally insulative material.

13. A battery unit according to claim 12, wherein said thermally insulative material is plastic or polymer.

14. A battery unit according to any of the preceding claims, further comprising a sensor or other means for sensing the temperature of said battery cell and generating data representative thereof.

15. A battery assembly comprising a battery unit according to any of claims 10 to 13 and a thermal management system, said thermal management system being configured to receive data representative of a temperature of said battery cell, determine if said temperature of said battery cell is within a predetermined range and, if not, generate one or more control signals configured to alter an operational status of said thermoelectric device so as to increase or decrease the heat of said first active side thereof, as required.

16. A battery module comprising at least two battery units according to any of claims 1 to 14, mounted side-by-side with a battery cell of a first battery unit being located adjacent a battery cell of a second battery unit, with a thermal barrier plate therebetween.

17. A battery pack comprising an array of battery modules according to claim 16.

18. A battery unit according to any of claims 1 to 9, wherein a graphite ribbon is thermally coupled at one end to an outer surface of said battery cell and thermally coupled at the other end to a thermoelectric device.

19. A battery unit according to claim 18, wherein each of a plurality of graphite

ribbons are thermally coupled at one end to an outer surface of said battery cell and thermally coupled at the other end to a thermoelectric device.

20. A battery unit according to claim 18, wherein said thermoelectric device is

provided in a thermal management system located remote from said battery unit.

21. A battery unit according to claim 19, wherein said thermal management system is configured to receive data representative of a temperature of said battery cell, determine if said temperature of said battery cell is within a predetermined range and, if not, generate one or more control signals configured to alter an operational status of said thermoelectric device so as to increase or decrease the heat of said first active side thereof, as required.

22. A battery pack comprising an array of battery cells, wherein adjacent battery cells are separated by a respective thermal barrier plate, each said battery cell being thermally coupled to a graphite ribbon at one end, the other end of said graphite ribbon being thermally coupled to a thermoelectric device located remotely from said battery pack.

23. A battery pack according to claim 22, wherein said thermoelectric device is

provided in a thermal management system located remote from said battery pack.

24. A battery pack according to claim 23, wherein said thermal management system is configured to receive data representative of a temperature of said battery cell, determine if said temperature of said battery cell is within a predetermined range and, if not, generate one or more control signals configured to alter an operational status of said thermoelectric device so as to increase or decrease the heat of said first active side thereof, as required.

25. A battery pack according to claim 23 or claim 24, each of a plurality of graphite ribbons are thermally coupled at one end to an outer surface of each said battery cell and thermally coupled at the other end to a thermoelectric device.