CH720605A1 - Flexible sheet-like sensor device for temperature distribution measurements in a battery pack - Google Patents

Abstract

A flexible sheet-like sensor device (1) according to the invention for temperature distribution measurements of a battery cell of a battery pack, comprises a flexible dielectric film (2) with a first surface (21) and a second surface (22) opposite the first surface (21); electrically conductive tracks (3) printed on the first surface (21) of the dielectric film (2), and a plurality of surface mount thermistors (4) arranged on the first surface (21) of the dielectric film (2). The surface mount thermistors (4) are electrically connected via the electrically conductive tracks (3), the plurality of surface mount thermistors (4) being distributed over the first surface (21) of the dielectric sheet (2) in order to measure the temperature distribution over a surface of an individual battery cell of the battery pack. The invention further relates to a battery pack with such a sensor device.

Description

technical field

[0001] The invention relates to a flexible sheet-like sensor device for temperature distribution measurements on a surface of battery cells in a battery pack.

Technical Background

[0002] Temperature monitoring in electric vehicle battery packs is of paramount importance for their longevity and optimal performance in addition to occupant safety. High operating temperatures increase the risk of thermal runaway for Li-ion batteries and accelerate their aging. Low temperatures limit the performance and charging capacities of batteries. Temperature data is also used to derive the state of charge (SOC), state of energy (SOE), and state of health (SOH) (commonly SoX) of a battery. Temperature gradients within a cell or among cells are undesirable as they introduce uneven aging rates.

[0003] Therefore, there is a need for detailed temperature monitoring and control within the battery pack, both in development stages and in use. However, this task is quite challenging due to significant temperature gradients within a battery cell or among batteries in a battery pack during operation.

[0004] Currently, only single or a few temperature sensors are used to monitor temperature in commercial battery packs, primarily to reduce the overall cost and complexity of the system. Increasing the number of sensors increases cost and occupies space. Therefore, temperature measurements for an electric vehicle's batteries are usually taken at the battery electrodes, connectors or somewhere on the external surface of the battery pack/module using thermal probes or thermistors. However, this is not sufficient for detailed temperature and temperature gradient monitoring. Also in this case the number of sensors and the location of measurements are limited. In addition, superficial temperature distribution measurements either between batteries or batteries and the cold plate are not possible.

[0005] Low profile printed sensors on a sensor film are considered a cost-effective solution for measuring a surface temperature distribution. A thin film thermistor deposited on an insulating film (EP2833374) or a plurality of printed resistors on a flexible substrate (EP3525279) have been proposed.

[0006] However, these printed sensors are susceptible to errors such as drift over time or cross-sensitivity to other physical phenomena such as pressure, making them unsuitable for precise measurements. The mentioned disadvantages may be due to, among other reasons, deterioration of a conductive ink over time, change in structure under pressure (e.g. due to "breathing" of battery cells) or electromagnetic interference.

[0007] Li-ion batteries are usually tightly packed in EV battery packs and therefore there is not enough space for bulky sensors, especially on side walls. In addition, the batteries exhibit some volume change during charging and discharging (breathing), temperature change and due to aging. These phenomena make the use of inflexible sensors quite challenging, especially when good contact between the sensor and the battery surface is desired under different conditions.

Brief Description of the Invention

[0008] It is an object of the invention to provide a temperature measuring device for a battery pack that solves the above-mentioned problems. It is a further object to provide a temperature measuring device for a battery pack that provides reliable measurements of a temperature distribution. It is a further object to provide a temperature measuring device for a battery pack that provides additional functionalities.

[0009] At least one of the objects 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 film having a first surface and a second surface opposite the first surface. Electrically conductive traces are printed on the first surface of the dielectric film. A plurality of surface mount thermistors (i.e., miniature surface mount electronic devices (SMD) containing a heat sensitive resistor) are arranged on the first surface of the dielectric film, the surface mount thermistors being electrically connected via the electrically conductive traces and the plurality of surface mount thermistors being distributed over the first surface of the dielectric sheet in order 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 film containing the electrically conductive traces and the plurality of surface mount thermistors. The elastomeric cover may form the flexible sheet-like sensor device having a uniform thickness.

[0010] The technical solution is therefore a thin, non-conductive substrate with printed conductive tracks and an encapsulated matrix of miniature surface-mount temperature sensors suitable for robustly monitoring a surface temperature distribution in a battery pack. Such a sensor sheet shall be at least partially in contact with at least one surface of one or more battery cells of a battery pack. In this way, the sensor sheet may provide additional functionalities as described below. Due to its flexibility, the sheet-like sensor device can be placed on different shapes and types of cells (e.g. cylindrical, prismatic or bag-shaped cells) and can accommodate dimensional changes due to breathing of the cells during charging and discharging processes.

[0011] The elastomeric cover is at least in line with the top surface of the thermistors to form the flexible sheet-like sensor device with a uniform thickness. The cover may also overlap or cover the thermistors. In other words, the thickness of the cover (or encapsulating material) may be at least the thickness of the thermistors or more.

[0012] The plurality of surface mount temperature sensors in the sensor sheet allows for better temperature monitoring of batteries to identify high surface temperature gradients and hotspots compared to current solutions that use a single or 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 operation. The use of miniature surface mount thermistors, which can have a maximum height of about 0.3 to 0.5 mm, further allows for obtaining robust temperature readings that are not affected by drawbacks such as drift and cross-sensitivity, as is known from printed temperature sensors. At the same time, the thickness of the sensor sheet can be kept low, even below 0.5 mm. The thickness depends predominantly on the size of the thermistors used. The less critical conductive traces for connecting the surface mount thermistors can be formed using cost-effective printing techniques to reduce the overall cost. The conductive tracks can be printed using, for example, screen or inkjet printing of a conductive ink containing, for example, conductive material such as silver.

[0013] The surface mount thermistors can be arranged in a two-dimensional array or a matrix with n columns and m rows. The thermistors can thus be evenly distributed over the entire surface of a cell to be measured. The number of surface mount thermistors and the arrangement are selected according to the desired spatial measurement resolution. Typically, the array comprises at least 3 by 3 surface mount thermistors.

[0014] The resistance change of the surface mount thermistors with temperature can be compared to a reference value (e.g. using a voltage divider configuration), from which the temperature is derived.

[0015] The flexible dielectric sheet may have a thickness of 100 to 200 micrometers and may be made of a dielectric polymer selected from the group of thermoplastic polymers and (synthetic or natural) rubbers, preferably polymers with good printability, thermal conductivity and adhesive properties for ink and the cover. Good results have been obtained with polyethylene terephthalate, thermoplastic polyurethane and polyimide. If elastomeric materials are chosen for the dielectric sheet, the sheet-like sensor device may be stretchable or elastic.

[0016] Encapsulation of the printed circuit and surface mount transistors is accomplished using elastomeric materials to protect the sensors and traces from the external environment (e.g., battery electrolyte) and may add additional functionality as described below. Encapsulation may be accomplished by sandwiching the sensor sheet (i.e., the flexible film containing the circuit and surface mount thermistors) between two layers of elastomer, by potting, by doctor blade coating, or other methods on one or both surfaces.

[0017] Further embodiments of the invention are set out in the dependent claims.

[0018] In some embodiments, the elastomeric cover may comprise a second elastomeric layer covering the second surface of the dielectric film; this elastomeric cover encapsulating the dielectric film containing the electrically conductive traces and the plurality of surface mount thermistors to form the flexible sheet-like sensor device having a uniform thickness.

[0019] The first and second elastomeric layers 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 equal to the thickness of the thermistors. On a surface without electrically conductive tracks and thermistors, the thickness may be a few micrometers. The first and second elastomeric layers may be made from an elastomeric material such as a natural rubber or a synthetic rubber, 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, fluorosilicone rubber, fluoro or perfluoro rubber, chlorosulfonate, acrylonitrile-butadiene rubber, halogenated acrylonitrile-butadiene rubber, carboxylated acrylonitrile-butadiene rubber, styrene-butadiene rubber, ethylene-acrylic rubber and polyacrylic rubber and mixtures and combinations thereof. The term "synthetic rubbers" should also be understood to include materials that may alternatively be broadly defined as thermoplastic or thermosetting elastomers, such as polyurethanes, silicones, fluorosilicone, styrene-isoprene-styrene copolymer, and styrene-butadiene-styrene copolymer, as well as other polymers that 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.

[0020] The first and second layers of elastomeric covering may extend beyond the edge of the dielectric film where they are bonded to each other.

[0021] In some embodiments, the second surface of the dielectric film may also be provided with printed electrically conductive traces and a plurality of surface mount thermistors. The arrangement may be the same as for the first surface.

[0022] In some embodiments, the dielectric sheet may include a connecting portion that extends over the elastomeric cover and provides electrical connection to the electrically conductive traces and the plurality of surface mount thermistors. To avoid large clusters of wires due to a large number of sensors, a multiplexer component may be used to connect the sensors of the flexible sheet-like sensor device to a readout electronics. The multiplexer component may be disposed on the connecting portion.

[0023] In some embodiments, the electrically conductive traces may comprise a circumferential thermistor-less, low resistance ground line. When a current is passed through the thermistor-less, low resistance ground line, the sensor sheet may be used as a heating element to heat the adjacent cell of the battery pack to achieve an optimal temperature, for example, in a case of rapid charging or in solid state batteries.

[0024] In some embodiments, the elastomeric cover comprises an elastomer and thermally conductive fillers selected from the group of, but not limited to, boron nitride, aluminum oxide, magnesium oxide, magnesium carbonate, magnesium hydroxide, silicon oxide, silicon nitride, aluminum nitride. A flexible sheet-like sensor device with such thermally conductive elastomers can be placed between a cold plate and a battery cell and additionally act as a thermal pad.

[0025] In some embodiments, the flexible dielectric film may be provided with at least one opening between the printed electrically conductive traces and the plurality of surface mount thermistors, preferably with an area of several square centimeters, to promote thermal conductivity through the flexible sheet-like sensor device. Preferably, several openings are distributed over all free areas of the dielectric film. This allows the flexible sheet-like sensor device to function as a temperature distribution sensor and at the same time as a thermal pad between cell walls and cooling plates.

[0026] In some embodiments, the flexible dielectric sheet may include a 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 chemical bonding of the elastomeric layers to the dielectric sheet material is insufficient. The holes may also serve to enhance thermal conductivity.

[0027] 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 pre-pressure for pouch cells). Other preferred properties of the material are a relatively flat strain-stress curve and low stress relaxation. In addition, the material may be fire retardant and may be able to withstand high forces (up to 30kN in the case of some pouch cells).

[0028] The presented flexible sheet-like sensor device can thus - in addition to measuring a temperature distribution - also include additional functionalities to serve as a compression pad between cells, a thermal pad between cells and adjacent cooling plates or as a heating element of cells.

[0029] The described flexible sheet-like sensor device can be used for thermal monitoring of batteries for electric vehicles and stationary battery applications.

[0030] If encapsulated with thermal interface material, it can be used as a thermal pad with monitoring capabilities for temperature distribution monitoring of electronic devices such as GPUs or CPUs, which have a significant surface area, generate a lot of heat, and whose surface temperature can vary significantly based on the design of the chip.

[0031] The invention further relates 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 a battery cell of the plurality of battery cells.

[0032] In some embodiments, the battery cells may be arranged side by side in a transverse direction (e.g., the largest surface of prismatic or rectangular cells 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.

[0033] In some embodiments, the at least one flexible sheet-like sensor device may cover the entire surface of the transverse side.

[0034] In some embodiments, the connection portion may extend across the plurality of battery cells to connect the plurality of surface mount thermistors to reading electronics.

Short explanation of the figures

[0035] The invention will be described in more detail below with reference to embodiments illustrated in the figures. The figures show in: Fig. 1 a schematic view of a flexible sheet-like sensor device; Fig. 2 a cross section A-A of the sensor device of Fig. 1; Fig. 3 a battery pack with a flexible sheet-like sensor device.

embodiments of the invention

[0036] Fig. 1 shows a schematic view of a flexible sheet-like sensor device 1 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 the line A-A.

[0037] The sensor device comprises a flexible dielectric film 2 which may be made of a dielectric polymer. Good results have been achieved using polyethylene terephthalate, thermoplastic polyurethane or polyimide, particularly in bonding the elastomeric layer and printing the conductive traces. The flexible dielectric film 2 has a first surface 21 and a second surface 22 opposite the first surface 21. In the example shown, the first surface is provided with a network of printed electrically conductive traces 3 and a plurality of surface mount thermistors 4 electrically connected to the traces 3. The surface mount thermistors 4 are evenly spaced in a two-dimensional array of, for example, three rows and four columns. The electrically conductive traces 3 are arranged such that areas between the thermistors 4 are free of traces and can therefore form large openings 24 in the dielectric film. The function of these openings 24 is explained below.

[0038] The electrically conductive tracks 3 further form a circumferential low resistance, thermistor-less ground line 31. By passing a current through the low resistance, thermistor-less ground line 31, the flexible sheet-like sensor device can be used as a heating element to heat the adjacent battery cell of the battery pack to achieve an optimum temperature, for example, during rapid charging or in solid state batteries.

[0039] The dielectric film 2 further comprises a connecting section 23 for connecting the electrically conductive tracks 3 and the thermistors 4 with reading electronics.

[0040] The flexible sheet-like sensor 1 further comprises an elastomeric cover 5 (shown as a dashed line in Fig. 1) containing a first and second layer 51, 52 and encapsulating the dielectric film 2 together with the electrically conductive traces 3 and the plurality of surface mount thermistors 4. The first layer 51 covers the first surface 21 of the dielectric film 2. The second layer 52 covers the second surface 22 of the dielectric film 2. Only the connecting portion 23 of the dielectric film 2 with its traces can extend outside the elastomeric cover 5 to provide electrical contact.

[0041] The first and second layers 51, 52 may extend beyond the edges of the dielectric sheet 2 where they are bonded together. Depending on the process used to apply the elastomeric material, bonding may or may not be visible. The elastomeric material of the elastomeric cover may be a natural or synthetic rubber, preferably ethylene propylene diene monomer rubber or liquid silicone rubber. If the dielectric sheet 2 is provided with large openings, these are also covered with the two layers 51, 52 of the elastomeric cover 5.

[0042] Fig. 3 shows a battery pack 6 with several rectangular 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.

[0043] The battery pack 6 shown comprises twelve battery cells 7, one of which is shown in a partially pulled out configuration to show the arrangement of the sensor device 1, which is also partially pulled out.

[0044] A connecting portion 23 of the sensor device 1 extends over the battery cells 7 to connect the plurality of surface mount thermistors 4 of the sensor device 1 to reading electronics.

REFERENCE SIGN

[0045] 1 flexible sheet-like sensor device 2 flexible dielectric film 21 first surface of dielectric film 22 second surface of dielectric film 23 connecting portion 24 opening 3 electrically conductive tracks 4 surface mount thermistor 5 elastomeric cover 51 first layer of elastomeric cover 52 second layer of elastomeric cover 6 battery pack 7 battery cell

Claims (15)

1. A flexible sheet-like sensor device (1) for temperature distribution measurements of a battery cell of a battery pack, comprising a flexible dielectric film (2) having a first surface (21) and a second surface (22) opposite the first surface (21); electrically conductive traces (3) printed on the first surface (21) of the dielectric film (2); a plurality of surface mount thermistors (4) arranged on the first surface (21) of the dielectric film (2), the surface mount thermistors (4) being electrically connected via the electrically conductive traces (3), and the plurality of surface mount thermistors (4) being distributed over the first surface (21) of the dielectric sheet (2) to measure the temperature distribution over a surface of a single battery cell of the battery pack. 2. The sensor device of 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 film (2) containing the electrically conductive traces (3) and the plurality of surface mount thermistors (4). 3. Sensor device according to claim 2, wherein the elastomeric cover (5) forms the flexible sheet-like sensor device (1) with a uniform thickness. 4. A 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 film (2); this elastomeric cover (5) encapsulating the dielectric film (2) containing the electrically conductive traces (3) and the plurality of surface mount thermistors (4) to form the flexible sheet-like sensor device (1) having a uniform thickness. 5. A sensor device according to claim 4, wherein the second surface (22) of the dielectric film (2) is provided with printed electrically conductive tracks (3) and a plurality of surface mount thermistors (4). 6. A sensor device according to any preceding claim, wherein the dielectric film (2) comprises a connecting portion (23) extending over the elastomeric cover (5) and providing an electrical connection to the electrically conductive traces (3) and the plurality of surface mount thermistors (4). 7. Sensor device according to one of the preceding claims, wherein the printed circuit comprises a circumferential ground line (31) without a thermistor and with low resistance. 8. Sensor device according to one of the preceding claims, wherein the elastomeric cover (5) comprises an elastomer and thermally conductive fillers. 9. A sensor device according to any preceding claim, wherein the flexible dielectric film (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. Sensor device according to one of claims 4 to 9, wherein the flexible dielectric film (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 sheet-like sensor device according to any preceding claim, wherein the at least one flexible sheet-like device is in contact with at least one surface of a battery cell of the plurality of battery cells. 12. The battery pack of 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 any one of claims 11 to 12, wherein the at least one flexible sheet-like sensor device covers the entire surface of the transverse side. 14. The battery pack of any of claims 11 to 13, wherein the connecting portion extends across the plurality of battery cells to connect the plurality of surface mount thermistors to readout electronics. 15. Battery pack according to one of claims 11 to 14, wherein the flexible sheet-like sensor device serves as a compression pad and/or thermal pad, which is preferably placed between a battery cell and an adjacent cooling plate.