A flexible sheet-like sensor device for temperature distribution measurements

Abstract

A flexible sheet-like sensor device (1) for temperature distribution measurements of a battery cell of a battery pack comprising a flexible, dielectric foil (2) with a first surface (21) and second surface (22) opposite the first surface (21); electrically conductive tracks (3) printed on the first surface (21) of the dielectric foil (2); a plurality of surface mount thermistors (4) arranged on the first surface (21) of the dielectric foil (2), the surface mount thermistors (4) being electrically connected via the electrically conductive tracks (3), wherein the plurality of surface-mounted thermistors (4) are distributed over the first surface (21) of the dielectric sheet (2) to be able to measure the temperature distribution over a surface of an individual battery cell of the battery pack.

Description

[0001] A flexible sheet-like sensor device for temperature distribution measurements

[0002] Technical Field

[0003] The invention relates to a flexible sheet-like sensor device for temperature distribution measurements on a surface of battery cells in a battery pack.

[0004] Technical Background

[0005] Temperature monitoring in electric vehicle battery packs is of utmost importance for their longevity and optimal performance in addition to passenger safety. High working temperatures increase the risk of thermal runaway for Li-ion batteries and accelerate their aging. Low temperatures limit the performance and charging capabilities of batteries. T emperature data is also used to infer battery state of charge (SOC), state of energy (SOE), and state of health (SOH) (in general, SoX). Temperature gradients within a cell or among cells are not desirable due to inducing non-uniform levels of aging.

[0006] Therefore, there is a need for detailed temperature monitoring and control in the battery pack both in development stages and in service. This task is, however, quite challenging due to significant temperature gradients within a battery cell or among batteries in a battery pack during operation.

[0007] Currently only single or a few temperature sensors are used to monitor the temperature in commercial battery packs, mainly to reduce the overall cost and complexity of the system. Increasing the number of sensors increases the cost and occupies space. Therefore, temperature measurements for the electric vehicle batteries are usually carried on the battery electrodes, connectors, or somewhere on the outer surface of the battery pack / module using thermocouples or thermistors. This however is not sufficient for detailed temperature and temperature gradient monitoring. Also, the number of sensors and the location of measurements are limited in this case. In addition, surface temperature distribution measurements either between batteries or batteries and the cooling plate are not possible.

[0008] Low-profile printed sensors on a sensor foil are considered as a low-cost solution to measure surface temperature distribution. A deposited thin-film thermistor on an insulating film (EP2833374), or plurality of printed resistors on a flexible substrate (EP3525279) have been proposed. However, these printed sensors are prone to artifacts such as drift over time or cross sensitivity to other physical phenomena such as pressure that makes them unsuitable for precise measurements. The mentioned shortcomings might be due to degradation of conductive ink over time, alteration of the structure with pressure (e.g. from the "breathing" of battery cells), or electromagnetic interference among other reasons.

[0009] Li-ion batteries are usually tightly packed in EV battery packs and thus there is not enough room for bulky sensors especially on side walls. Additionally, the batteries exhibit certain volume change with charge and discharge (breathing), with temperature change, and due to aging. These phenomena make the use of inflexible sensors rather challenging especially when a good contact between the sensor and the battery surface in various conditions is desired.

[0010] Summary of the Invention

[0011] It is an objective of the invention to provide a temperature measuring device for battery pack, which solves the above-mentioned problems. It is a further objective to provide a temperature measuring device for battery pack, which provides reliable measurements of temperature distribution. It is a further objective to provide a temperature measuring device for a battery pack, which provides additional functionalities.

[0012] At least one of the objectives of the present invention is achieved by a flexible sheet-like sensor device for temperature distribution measurements of a battery cell of a battery pack according to claim 1. The flexible sheet-like device comprises a flexible, dielectric foil with a first surface and second surface opposite the first surface. Electrically conductive tracks are printed on the first surface of the dielectric foil. A plurality of surface mount thermistors (i.e. a miniature electronic surface mounted device (SMD) including a thermally-sensitive resistor) are arranged on the first surface of the dielectric foil, the surface mount thermistors being electrically connected via the electrically conductive tracks, wherein the plurality of surface-mounted thermistors are distributed over the first surface of the dielectric sheet to be able to measure the temperature distribution over a large surface of the battery cell of the battery pack. The flexible sheet-like device may further comprise an elastomeric cover comprising a first layer covering the first surface of the dielectric foil including the electrically conductive tracks and the plurality of surface mount thermistors. The elastomeric cover may form the flexible sheet-like sensor device having an even thickness.

[0013] The technical solution is thus a thin non-conductive substrate with printed conductive tracks and an encapsulated matrix of miniature surface-mount temperature sensors, suitable for robust monitoring of surface temperature distribution in a battery pack. Such a sensor sheet is intended to be in contact at least partially with at least a surface of one or more battery cells of a battery pack. In this way, the sensor sheet can provide additional functionalities as explained below. Due to its flexibility the sheet-like sensor device may be placed on different forms and types of cells (e.g. cylindric, prismatic or pouch-like cells) and may adapt to dimensional changes due to breathing of the cells during charging and de-charging processes.

[0014] The elastomeric cover is at least in line with the top surface of the thermistors to form the flexible sheet-like sensor device with an even thickness. The cover may also overlap or cover the thermistors. In other words, the thickness of the cover (or encapsulant) may be at least the thickness of the thermistors, or more.

[0015] The plurality of surface mount temperature sensors in the sensor sheet allows to perform a better temperature monitoring of batteries to identify high surface temperature gradients and hotspots compared to current solutions, which use a single or a few sensors per module. The temperature data can be used to optimize the thermal management solution, and charge and discharge parameters during the battery pack design phase and to improve the longevity and safety of the pack during service. The use of miniature surface mount thermistors, which may have a maximal height of approx. 0.3 to 0.5 mm, further allows to obtain robust temperature readings that are not inversely affected by shortcomings such as drift and cross sensitivity as known from printed temperature sensors. At the same time, the thickness of the sensor sheet may be kept low, even less than 0.5 mm. The thickness mainly depends on the size of thermistors used. The less critical conductive tracks for connecting the surface mount thermistors may be formed using cost-efficient printing techniques to reduce the overall cost. The conductive tracks may be printed using e.g. screen or inkjet printing of a conductive ink including e.g. conductive material such as silver.

[0016] The surface mount thermistors may be arranged in a two-dimensional array or matrix with n columns and m lines. The thermistors may thereby be evenly distributed over the entire surface of a cell to be measured. The number of surface mount thermistors and the arrangement are chosen according to the desired spatial measurement resolution. Typically, the array comprises at least 3 by 3 surface-mount thermistors.

[0017] The resistance change of the surface mount thermistors with temperature may be compared to a reference value (e.g., using a voltage divider configuration) from which the temperature is inferred. The flexible, dielectric foil may have a thickness of 100 to 200 micrometre and may be made of a dielectric polymer selected from the group of thermoplastic polymers and rubbers (synthetic or natural), preferably polymers with good printability, heat conductivity and adhesive properties for ink and the cover. Good results have been achieved with Polyethylene terephthalate, thermoplastic polyurethane, polyimide. When choosing elastomeric materials for the dielectric foil, the sheet-like sensor device may be stretchable or elastic.

[0018] The encapsulation of the printed circuit and the surface mount transistors is done using elastomeric materials to protect the sensors and tracks from external environment (e.g. battery electrolyte) and may add additional functionalities as described below. The encapsulation can be done by sandwiching the sensor sheet (i.e. the flexible foil with the circuit and the surface mount thermistors) between two layers of elastomer, by potting, by blade coating or other methods on one or both surfaces.

[0019] Further embodiments of the invention are set forth in the dependent claims.

[0020] In some embodiments the elastomeric cover may comprise a second elastomeric layer covering the second surface of the dielectric foil; said elastomeric cover encapsulating the dielectric foil including the electrically conductive tracks and the plurality of surface mount thermistors to form the flexible sheet-like sensor device with an even thickness.

[0021] The first and second elastomeric layer may each have a thickness of up to 2 mm. On the side of the electrically conductive tracks and the thermistors, the thickness of the elastomeric layer should be at least the thickness of the thermistor. On a surface without electrically conductive tracks and thermistors the thickness may be a few micrometres. The first and second elastomeric layer may be made of an elastomer material such as a natural rubber or a synthetic rubber, such as butyl rubber or halogenated butyl rubber (e.g. bromobutyl rubber), isoprene rubber, butadiene rubber, ethylene propylene copolymer rubber, ethylene-propylene-diene monomer rubber, silicone rubber, fluoro silicone rubber, fluoro- or perfluoro- rubbers, chlorosulfonate, acrylonitrile butadiene rubber, halogenated acrylonitrile butadiene rubber, carboxylated acrylonitrile butadiene rubber, styrene butadiene rubber, ethylene acrylic rubber and polyacrylic rubber, and blends and combinations thereof. The term "synthetic rubbers" also should be understood to encompass materials which alternatively may be classified broadly as thermoplastic or thermosetting elastomers such as polyurethanes, silicones, fluorosilicones, styrene- isoprene-styrene copolymer, and styrene-butadiene-styrene copolymer, as well as other polymers which exhibit rubber-like properties such as plasticized nylons, polyolefins, polyesters, ethylene vinyl acetates, fluoropolymers, and polyvinyl chloride. Preferred materials are ethylene propylene diene monomer rubber or liquid silicone rubber.

[0022] The first and the second layer of the elastomeric cover may extend over the edge of the dielectric foil where they are bonded to each other.

[0023] In some embodiments the second surface of the dielectric foil may also be provided with printed electrically conductive tracks and a plurality of surface mount thermistors. The arrangement may be the same as for the first surface.

[0024] In some embodiments the dielectric foil may comprise a connector portion extending over the elastomeric cover and providing an electrical connection to the electrically conductive tracks and the plurality of surface mount thermistors. To avoid large clusters of wires due to large number of sensors, a multiplexer component may be used to connect the sensors of the flexible sheet-like sensor device to readout electronics. The multiplexer component may be arranged on the connector portion.

[0025] In some embodiments the electrically conductive tracks may comprise a low-resistance thermistor-less circumferential ground line. By passing a current through the low-resistance thermistor-less ground line, the sensor sheet can be used as a heater to heat up the adjacent cell of the battery pack to reach optimal temperature for example in case of rapid charging or in solid-state batteries.

[0026] In some embodiments the elastomeric cover comprises an elastomer and thermally conductive fillers selected from the group of boron nitride, aluminium oxide, magnesium oxide, magnesium carbonate, magnesium hydroxide, silicon oxide, silicon nitride, aluminium nitride, but not limited to. A flexible sheet-like sensor device with such thermally conductive elastomers may be placed between a cooling plate and a battery cell, acting additionally as a thermal pad.

[0027] In some embodiments the flexible, dielectric foil may be provided with at least one opening between the printed electrically conductive tracks and the plurality of surface mount thermistors, preferably of several square centimetres, to promote thermal conductivity through the flexible sheet-like sensor device. Preferably, several openings are distributed over all free areas of the dielectric foil. Thereby, the flexible, sheet-like sensor device may function as a temperature distribution sensor and at the same time as thermal pad between cell walls and cooling plates.

[0028] In some embodiments the flexible, dielectric foil may comprise plurality of holes forming a plurality of bonding areas for the first and second elastomeric layers of the elastomeric cover. This may be of particular interest, when the chemical bonding of the elastomeric layers to the material of the dielectric foil is not sufficient. The holes may also serve to enhance thermal conductivity.

[0029] In some embodiments the material and dimension of the elastomeric cover may have a low compression set (e.g. to compensate for breathing of the cells in the battery pack, or to ensure proper pre-pressure for pouch cells). Further preferred characteristics of the material are a relatively flat strain-stress curve, low stress relaxation. In addition, the material may be fire retardant and may be able to withstand high forces (up to 30kN in case of some pouch cells).

[0030] The presented flexible, sheet-like sensor device may thus - in addition to measuring a temperature distribution - also incorporate additional functionalities of acting as a compression pad between cells, a thermal pad between cells and adjacent cooling plates or as a heater of cells.

[0031] The described flexible sheet-like sensor device may be used for thermal monitoring of batteries for electric vehicles and stationary battery applications.

[0032] If encapsulated with thermal interface material it may be used as a thermal pad with monitoring capabilities for temperature distribution monitoring of electronic devices like GPUs or CPUs that have substantial surface area, produce a lot of heat, and their surface temperature might vary considerably based on the design of the chip.

[0033] The invention further refers to a battery pack comprising a plurality of battery cells and at least one flexible sheet-like sensor device as described above, wherein the at least one flexible sheet-like device is in contact with at least one surface of one battery cell of the plurality of battery cells.

[0034] In some embodiments the battery cells may be arranged side by side in a transverse direction (e.g. the largest surface of a prismatic or rectangular cell are adjacent to each other) and the at least one flexible sheet-like sensor device is arranged between the transverse sides of two adjacent battery cells.

[0035] In some embodiments the at least one flexible sheet-like sensor device may cover the entire surface of the transverse side.

[0036] In some embodiments the connector portion may extend over the plurality of battery cells for connecting the plurality of surface mount thermistors to readout electronics. Brief Explanation of the Figures

[0037] The invention is described in greater detail below with reference to embodiments that are illustrated in the figures. The figures show:

[0038] Fig. 1 a schematic view of a flexible, sheet-like sensor device;

[0039] Fig. 2 a cross section A-A of the sensor device of Fig. 1 ;

[0040] Fig. 3 a battery pack with a flexible, sheet-like sensor device.

[0041] Embodiments of the Invention

[0042] Fig. 1 shows schematic view of a flexible, sheet-like sensor 1 device for measuring a temperature distribution between battery cells 7 of a battery pack 6 (see Fig. 3). Fig. 2 shows a cross-section of the flexible, sheet-like sensor 1 of Fig. 1 along line A-A.

[0043] The sensor device comprises a flexible, dielectric foil 2, which may be made of a dielectric polymer. Good results have been achieved using polyethylene terephthalate, thermoplastic polyurethane, or polyimide, especially for bonding the elastomeric layer and printing the conductive tracks. The flexible, dielectric foil 2 has a first surface 21 and a second surface 22 opposite the first surface 21. In the shown example, the first surface is provided with a network of printed electrically conductive tracks 3 and a plurality of surface mount thermistors 4 electrically connected to the tracks 3. The surface mount thermistors 4 are arranged evenly spaced in a two-dimensional array with e.g. three lines and four columns. The electrically conductive tracks 3 are arranged in a manner that large areas between the thermistors 4 are free of tracks and therefore may form large openings 24 in the dielectric foil. The function of these openings 24 is explained below.

[0044] The electrically conductive tracks 3 further form a low-resistance thermistor-less circumferential ground line 31. By passing a current through the low-resistance thermistorless ground line, the flexible, sheet-like sensor device can be used as a heater to heat up the adjacent battery cell of the battery pack to reach optimal temperature for example in case of rapid charging or in solid-state batteries.

[0045] The dielectric foil 2 further comprises a connector portion 23 for connecting the electrically conductive tracks 3 and the thermistors 4 to readout electronics.

[0046] The flexible, sheet-like sensor 1 further comprises an elastomeric cover 5 (shown as dashline in Fig. 1) including a first and second layer 51 , 52 and encapsulating the dielectric foil 2 together with the electrically conductive tracks 3 and the plurality of surface mount thermistors 4. The first layer 51 covers the first surface 21 of the dielectric foil 2. The second layer 52 covers the second surface 22 of the dielectric foil 2. Only the connector portion 23 of the dielectric foil 2 with its tracks may extend out of the elastomeric cover 5 for providing electrical contact.

[0047] The first and second layers 51 , 52 may extend over the edges of the dielectric foil 2, where they our bonded to each other. Depending on the process used for applying the elastomeric material, a bonding may be visible or not. The elastomeric material of the elastomeric cover 5 may be a natural or synthetic rubber, preferably ethylene propylene diene monomer rubber or liquid silicone rubber. If the dielectric foil is provided with large opening, these are also covered with the two layers 51 , 52 of the elastomeric cover 5.

[0048] Fig. 3 shows a battery pack 6 with several rectangular shaped battery cells 7 arranged side by side in a transverse direction. One or more flexible, sheet-like sensor devices are arranged between adjacent battery cells 7 of the battery pack 6. The sensor devices are dimensioned to cover the entire transverse surface of the battery cells 7.

[0049] The shown battery pack 6 has twelve battery cells 7 whereof one is shown in a partially pulled out configuration to depict the arrangement of the sensor device 1 , which is also partially pulled out.

[0050] A connector portion 23 of the sensor device 1 extends over the battery cells 7 for connecting the plurality of surface mount thermistors of the sensor device 1 to readout electronics.

[0051] Reference Signs

[0052] 1 flexible sheet-like sensor device

[0053] 2 flexible, dielectric foil

[0054] 21 first surface of dielectric foil

[0055] 22 second surface of dielectric foil

[0056] 23 connector portion

[0057] 24 opening

[0058] 3 electrically conductive tracks

[0059] 4 surface mount thermistor

[0060] 5 elastomeric cover

[0061] 51 first layer of elastomeric cover second layer of elastomeric cover battery pack battery cell

Claims

Claims1 . A flexible sheet-like sensor device (1) for temperature distribution measurements of a battery cell of a battery pack comprising a flexible, dielectric foil (2) with a first surface (21) and second surface (22) opposite the first surface (21); electrically conductive tracks (3) printed on the first surface (21) of the dielectric foil(2); a plurality of surface mount thermistors (4) arranged on the first surface (21) of the dielectric foil (2), the surface mount thermistors (4) being electrically connected via the electrically conductive tracks (3), wherein the plurality of surface-mounted thermistors (4) are distributed over the first surface (21) of the dielectric sheet (2) to be able to measure the temperature distribution over a surface of an individual battery cell of the battery pack.

2. The sensor device according to claim 1 , wherein the flexible sheet-like sensor device(1) further comprises an elastomeric cover (5) comprising a first layer (51) covering the first surface (21) of the dielectric foil (2) including the electrically conductive tracks(3) and the plurality of surface mount thermistors (4).

3. The sensor device according to claim 2, wherein the elastomeric cover (5) forms the flexible sheet-like sensor device (1) having an even thickness.

4. The sensor device according to claim 2 or 3, wherein the elastomeric cover (5) comprises a second elastomeric layer (52) covering the second surface (22) of the dielectric foil (2); said elastomeric cover (5) encapsulating the dielectric foil (2) including the electrically conductive tracks (3) and the plurality of surface mount thermistors (4) to form the flexible sheet-like sensor device (1) with an even thickness.

5. The sensor device according to claim 4, wherein the second surface (22) of the dielectric foil (2) is provided with printed electrically conductive tracks (3) and a plurality of surface mount thermistors (4).

6. The sensor device according to one of the preceding claims, wherein the dielectric foil(2) comprises a connector portion (23) extending over the elastomeric cover (5) andproviding an electrical connection to the electrically conductive tracks (3) and the plurality of surface mount thermistors (4).

7. The sensor device according to one of the preceding claims, wherein the printed circuit comprises a low-resistance thermistor-less circumferential ground line (31).

8. The sensor device according to one of the preceding claims, wherein the elastomeric cover (5) comprises an elastomer and thermally conductive fillers.

9. The sensor device according to one of the preceding claims, wherein the flexible, dielectric foil (2) is provided with at least one opening (24) between the printed electrically conductive tracks (3) and the plurality of surface mount thermistors (4).

10. The sensor device according to one of the claims 4 to 9, wherein the flexible, dielectric foil (2) comprises a plurality of holes forming a plurality of bonding areas for the first and second elastomeric layers of the elastomeric cover (5).

11. A battery pack comprising a plurality of battery cells and at least one flexible sheetlike sensor device according to one of the preceding claims, wherein the at least one flexible sheet-like device is in contact with at least one surface of one battery cell of the plurality of battery cells.

12. A battery pack according to claim 11 , wherein the battery cells are arranged side by side in a transverse direction and the at least one flexible sheet-like sensor device is arranged between the transverse sides of two adjacent battery cells.

13. A battery pack according to one of the claims 11 to 12, wherein the at least one flexible sheet-like sensor device covers the entire surface of the transverse side.

14. A battery pack according to one of the claims 11 to 13, wherein the connector portion extends over the plurality of battery cells for connecting the plurality of surface mount thermistors to readout electronics.

15. A battery pack according to one of the claims 11 to 14, wherein the flexible sheet-like sensor device functions as a compression pad and / or a thermal pad, preferably placed between a battery cell and an adjacent cooling plate.

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