Energy storage and parallel connectors

Abstract

An energy storage device (10) comprises a plurality of electrically connected electrochemical cells (12), at least two of which are connected in parallel by means of a parallel connector (14). The parallel connector (14) comprises a material (19) of medium electrical conductivity, which includes a matrix of electrically non-conductive material and a conductivity modifier of an electrically conductive material distributed in the matrix. Furthermore, a parallel connector is specified.

Description

[0001] The invention relates to an energy storage device comprising a plurality of electrically connected electrochemical cells and a parallel connector for such an energy storage device.

[0002] In order to provide the desired performance, energy storage systems usually comprise a large number of electrochemical cells that are electrically interconnected in series and / or parallel, for example in high-voltage storage systems for at least partially electrically powered motor vehicles such as hybrid and electric vehicles.

[0003] To provide the electrical connections, series and parallel connectors are used. Parallel connectors connect electrochemical cells that essentially have the same voltage level and are linked together by the parallel connectors to form so-called "logic cells." The voltage of the logic cells can be monitored by a battery management system of the energy storage system.

[0004] Furthermore, balancing currents can flow between the electrochemical cells of the respective logic cell via the parallel connector to equalize the voltage levels of the individual electrochemical cells. This process is also referred to here as "cell balancing" and is to be distinguished from the balancing of series-connected logic cells that are connected in parallel on the voltage side via switches such as MOSFETs (active balancing) or are "short-circuited" via a balancing resistor and a switch (passive balancing).

[0005] The serial connectors, in turn, connect the logic cells serially, thus electrically connecting the logic cells in series, resulting in strings of serially connected electrochemical cells.

[0006] Thus, serial and parallel current paths can be distinguished within the energy storage system.

[0007] It is known that parallel connectors should be designed to be as robust as possible so that, in the event of a short circuit in an electrochemical cell, they have a current-carrying capacity sufficient to trip a fuse arranged in series. Such fuses trip at currents in the range of several hundred amperes, for example, approximately 200 to 400 A, which necessitates correspondingly thick parallel connectors capable of carrying such currents. This results in the parallel connectors being over-dimensioned with regard to the currents handled for cell balancing during the fault-free operation of the energy storage system, which only need to compensate for voltage differences of a few millivolts. This negatively impacts the installation space available for other components of the energy storage system and limits the achievable specific energy density of the energy storage system.Furthermore, the high currents generate thermal power in the parallel connector, which can be sufficient to heat other electrochemical cells beyond their permissible maximum temperature, potentially causing them to short-circuit as well. This effect must be counteracted, for example, with complex cooling systems.

[0008] The object of the invention is to provide an energy storage device that enables reliable handling of short circuits in electrochemical cells. In particular, the energy storage device should allow for optimized use of installation space.

[0009] The object of the invention is achieved by an energy storage device comprising a plurality of electrically connected electrochemical cells, at least two of which are connected in parallel by means of a parallel connector. The parallel connector comprises a material of medium electrical conductivity, which includes a matrix of electrically non-conductive material and a conductivity modifier made of an electrically conductive material distributed in the matrix.

[0010] The invention is based on the fundamental idea of ​​using a parallel connector that has a medium electrical conductivity, i.e., neither such a high conductivity that currents of several hundred amperes, for example 200 A or more, can flow through the parallel connector in the event of a short circuit, nor such a low conductivity that no or almost no current flow occurs between the parallel-connected electrochemical cells in the event of a short circuit and the parallel connector would act like a kind of switch or disconnect switch.

[0011] In other words, parallel connectors are used whose resistance is designed such that, in the event of a short circuit in one of the electrochemical cells, a current can flow through the parallel connector(s) in a logic cell containing the short-circuited electrochemical cell. This current remains below a defined threshold, allowing for a controlled discharge of the electrochemical cells in the affected logic cell within a predetermined time period. In this way, the temperature rise occurring within the energy storage system in the event of a short circuit is limited, enabling the heat generated by equalization processes within the energy storage system to be dissipated without risking harmful temperature effects on other electrochemical cells in the energy storage system.In detail, the temperature rise in the electrochemical cells connected in parallel to the short-circuited electrochemical cell via the parallel connector is limited by restricting the current and preventing excessively rapid deep discharge, which would result in a significant drop in power. This effectively prevents thermal propagation within the energy storage system. This effect is further enhanced by the fact that the current of compensating currents contributes quadratically to the thermal load; therefore, reducing the maximum current significantly limits the thermal load.In this way, the load on the internal resistance of the electrochemical cell is also reduced, which can particularly effectively prevent the electrolyte of the electrochemical cells from evaporating and / or decomposing, thus effectively preventing a pressure increase within the energy storage device and / or ignition of active materials in the electrochemical cell.

[0012] The conductivity that the parallel connector for the respective energy storage device must have in order to produce this behavior is adjustable according to the invention via a material of medium electrical conductivity which has a matrix of a material that is not electrically conductive in itself, but whose electrical conductivity is adjusted via the conductivity modifier introduced into the matrix, i.e., set to a desired value.

[0013] The electrical conductivity of the material can be adjusted to the desired value both by the type of conductivity modifier and by the weight fraction or fill level of the conductivity modifier in the material of medium electrical conductivity.

[0014] The material with medium electrical conductivity can therefore be considered a "filled non-conducting material".

[0015] In particular, the use of fuses in the serial path can be dispensed with, since the use of appropriately designed parallel connectors prevents currents of a magnitude that would need to be prevented by such a fuse.

[0016] However, it is also fundamentally conceivable to continue to maintain backups in the serial path in order to provide redundant protection for the energy storage system.

[0017] The material with medium electrical conductivity can have an electrical resistance in the range of 1 to 1000 Ω, preferably 1 to 100 Ω, and more preferably greater than 1 to 10 Ω. An electrical resistance of less than 1 Ω results in materials whose electrical conductivity is so high that, in the event of a short circuit, currents can occur that cause an excessive temperature increase within the energy storage device, thus necessitating fuses in the series path and / or additional cooling devices. An electrical resistance of more than 1000 Ω results in materials whose electrical conductivity is so low that, in the event of a short circuit, even the necessary small equalizing currents between the parallel-connected electrochemical cells are suppressed, and the parallel connector thus acts as a kind of insulating disconnect switch.Furthermore, with an electrical resistance of more than 1000 Ω, the electrical conductivity can be so low that the equalizing currents necessary for the desired equalization of voltage levels in the normal operation of the energy storage system can no longer flow.

[0018] In one variant, the material with medium electrical conductivity is a filled plastic.

[0019] In another variant, the material with medium electrical conductivity is a filled varnish or a filled adhesive.

[0020] Plastics, coatings, and adhesives are already used in known energy storage devices, for example, to arrange, align, stiffen, or secure the electrochemical cells within the device. By replacing such components with a material of medium electrical conductivity, the known functions can be extended to include the desired electrical connection, thus eliminating the need for additional components. This reduces the installation space required for the energy storage device and / or allows for an increase in its specific energy capacity while maintaining the same overall size. In particular, the arrangement of series and parallel connectors can be flexibly designed, with the significant advantage that the series and parallel connectors do not need to be located on the same side of the respective electrochemical cell, for example, on the same end face.

[0021] The type of filled plastic, filled lacquer and filled adhesive is not fundamentally restricted, as long as the desired electrical conductivity can be achieved.

[0022] For example, the filled plastic comprises or consists of PEDOT:PSS. Possible variants of such plastics are described in Xia et al.: “Review on applications of PEDOTs and PEDOT:PSS in perovskite solar cells” (Journal of Materials Science: Materials in Electronics (2021), 32:12746-12757, doi: 10.1007 / s10854-020-03473-w).

[0023] In principle, any plastic can serve as a matrix for the material with medium electrical conductivity. For example, the matrix material can be selected from the group of polyolefins, polyesters, polyketones, polythiophenes, and combinations thereof.

[0024] The filled lacquer and the filled adhesive can be polyurethane- or epoxy resin-based systems in which a matrix of polyurethane or epoxy resin is provided with the conductivity modifier.

[0025] The filled adhesive can be a 1K or a 2K adhesive. In particular, the use of a 1K adhesive allows for faster process control in the production of the energy storage device, while a 2K adhesive allows for particularly flexible process control.

[0026] The electrically conductive material can be selected from the group consisting of carbon, soot, carbon nanotubes, metal particles and combinations thereof.

[0027] Carbon species, in particular, are suitable for imparting the desired electrical conductivity to materials with medium electrical conductivity. The influence of exemplary carbon allotropes is described in Alig et al.: “Filler Networks of Carbon Allotropes of Different Shapes and Dimensions in a Polymer Matrix” (Advances in Dielectrics. Springer, Cham, 2022, doi: 10.1007 / 978-3-030-89723-9_10) and in Alig et al.: “Establishment, morphology and properties of carbon nanotube networks in polymer melts” (Polymer 53 (2012), pp. 4–28, doi: 10.1016 / j.polymer.2011.10.063).

[0028] The metal particles of the electrically conductive material are in particular metal particles made of silver, aluminum, copper, iron, stainless steel and combinations thereof.

[0029] The fill level of the conductivity modifier in the medium electrical conductivity material is particularly 50% or more, preferably in the range of 50 to 60%. A fill level of less than 50% can lead to materials that do not exhibit electrical conductivity in the desired range.

[0030] The medium-conductivity material can also include a contact improver that enhances the adhesion of the medium-conductivity material to the respective electrochemical cells. Contact improvers can be additives that improve adhesion between the medium-conductivity material and the electrochemical cells, or mechanical elements, such as antennas and wires, that are embedded in the matrix of the medium-conductivity material.

[0031] The parallel connector can be contacted with a lateral surface and / or an end face of the respective electrochemical cells. The parallel connector of the energy storage system is thus characterized by particularly high flexibility in its arrangement and enables the electrochemical cells to be electrically interconnected in a space-optimized manner. This is especially advantageous in energy storage systems manufactured using a "cell-to-pack" or "cell-to-open-body" process, in which no separate energy storage modules are used, but rather the available installation space is filled as completely as possible by electrochemical cells that are interconnected to form the energy storage system via parallel and series connectors with corresponding series and parallel current paths.

[0032] Preferably, series and parallel connectors are contacted on different surfaces of the respective electrochemical cells, for example on different end faces, or one of the connectors is attached to one of the end faces and the other of the connectors to the outer surface of the electrochemical cell.

[0033] The parallel connector can simultaneously serve as a cell holder for the electrochemical cells connected in parallel by the parallel connector. In this sense, the parallel connector can fulfill a dual function, namely, on the one hand, establishing the electrical connection between the electrochemical cells and, on the other hand, at least contributing to their arrangement and mounting within the energy storage device. Corresponding cell holders in known energy storage devices can be made of a non-conductive plastic, adhesive, or foam, which can thus be replaced by the parallel connector according to the invention, which has the desired electrical conductivity.

[0034] In another variant, the parallel connector comprises contact sections and a conductive section connecting these contact sections. The contact sections are in direct contact with the electrochemical cells connected by the parallel connector and are made of an electrically conductive material. Because at least the contact sections are made of an electrically conductive material, the electrical conductivity of both the contact sections and the conductive section is determined by the electrical conductivity of the medium-conductivity material. Therefore, the conductive section can be made of a material with the same or even higher electrical conductivity than the medium-conductivity material without negatively affecting the overall electrical conductivity of the parallel connector.

[0035] It is also possible that both the contact sections and the conductive section are made of a material with medium electrical conductivity. In particular, the entire parallel connector is made of a material with medium electrical conductivity.

[0036] The parallel connector can be multi-part, especially two-part. A multi-part parallel connector minimizes shear effects, resulting in improved mechanical strength. Particularly when a parallel connector is made of a relatively flexible material, such as filled adhesive, this further increases its service life and reliability.

[0037] The energy storage device is preferably an energy storage device for a motor vehicle, for example a motor vehicle that is at least partially electrically powered, such as a hybrid or electric vehicle.

[0038] The object of the invention is further achieved by a parallel connector for an energy storage device, in particular an energy storage device as described above, comprising a plurality of electrically connected electrochemical cells, wherein the parallel connector comprises a material of medium electrical conductivity, comprising a matrix of electrically non-conductive material and a conductivity modifier of an electrically conductive material distributed in the matrix.

[0039] The features and properties of the energy storage device according to the invention apply analogously to the parallel connector according to the invention and vice versa.

[0040] Further features and characteristics will become apparent from the following description of selected embodiments, which are not to be understood in a restrictive sense, as well as from the drawings. These show: - Fig. 1 schematically an energy storage device according to the invention with parallel connectors according to the invention, - Fig. 2 selected parts of a first embodiment of the energy storage device made of Fig. 1 in a perspective view, - Fig. 3 selected parts of a second embodiment of the energy storage device made of Fig. 1 in a perspective view, - Fig. 4 a sectional view through selected parts of a third embodiment of the energy storage device Fig. 1, and - Fig. 5 a sectional view through selected parts of a fourth embodiment of the energy storage device Fig. 1.

[0041] Fig. Figure 1 schematically shows an energy storage device 10 according to the invention for a motor vehicle, for example a hybrid or electric vehicle.

[0042] The energy storage device 10 has a plurality of electrically interconnected electrochemical cells 12. The electrochemical cells 12 are configured to store and release electrical energy. In other words, the energy storage device 10 according to the invention is a secondary battery, for example a lithium-ion battery.

[0043] Each selected electrochemical cell 12 is connected via parallel connectors 14 according to the invention (in Fig. (1 illustrated by dash-dot lines) to logical cells 16 electrically connected to each other, i.e. electrically connected in parallel to each other.

[0044] In the embodiment in Fig. In 1, three electrochemical cells 12 are connected to form a logical cell 16. It is understood that only two or more than three electrochemical cells 12 can also form a logical cell 16.

[0045] The capacity of the energy storage device 10 can be influenced in particular by the number of electrochemical cells 12 per logical cell 16, whereby a higher number of electrochemical cells 12 per logical cell 16 results in a higher capacity.

[0046] Within each of the logic cells 16, the associated electrochemical cells 12 exhibit essentially the same voltage level. This means that all electrochemical cells 12 of a logic cell 16 have essentially the same voltage, apart from unavoidable fluctuations, which are primarily due to manufacturing and aging effects. Such fluctuations are typically in the range of a few millivolts.

[0047] Equalizing currents can therefore flow via the parallel connectors 14, which connect the respective electrochemical cells 12 to each other, thereby equalizing the voltages of the electrochemical cells 12. This process is also known as cell balancing and contributes to extending the service life of the energy storage device 10.

[0048] In order to determine the voltage level of each of the logic cells 16, the energy storage device 10 has a voltage measuring device 18 which includes several voltage measuring units 20, namely one voltage measuring unit 20 for each of the logic cells 16.

[0049] The voltage measuring device 18 is in particular a component of a (not further shown) battery management system of the energy storage device 10.

[0050] The parallel connectors 14 comprise a material 19 of medium electrical conductivity (cf. Fig. 2), which comprises a matrix of electrically non-conductive material and a conductivity modifier distributed in the matrix made of an electrically conductive material, and which will be discussed in more detail later.

[0051] The material 19, with medium electrical conductivity, exhibits an electrical resistance in the range of 1 to 100 Ω, particularly in the range greater than 1 to 10 Ω. The electrical resistance, in turn, determines the maximum current that can flow between the electrochemical cells 12 of a logic cell 16.

[0052] As in Fig. As can be seen in Figure 1, the logic cells 16 are electrically connected to each other via serial connectors 22. In other words, the electrochemical cells 12 of the logic cells 16 are connected in series via the serial connectors 22 and form strands of electrochemical cells 12, where the number of strands corresponds to the number of electrochemical cells 12 per logic cell 16.

[0053] Accordingly, the energy storage device 10 in the embodiment shown has a first strand 24, a second strand 26 and a third strand 28 made up of serially connected electrochemical cells 12.

[0054] By connecting the logic cells 16 in series, the voltage supplied by the energy storage device 10 via electrical connections 30 and 32 is set to a desired value, for example to a value of 400 V or more.

[0055] The number of electrochemical cells 12 per strand 24 to 28 depends on the desired voltage of the energy storage device 10, as shown by a dotted connection in Fig. 1 is indicated. Accordingly, it is understood that the energy storage device 10 can have more or fewer electrochemical cells 12 and logical cells 16 than in Fig. 1 shown.

[0056] The logic cells 16 are free of electrical fuses. In other words, the parallel connectors 14 do constitute a resistive element that selectively limits the current flow. However, no fuse is provided to interrupt the electrical connection between the electrochemical cells 12 of a logic cell 16 at a predetermined current.

[0057] Likewise, the serial connectors 22, and the strands 24 to 28 in total, consisting of serially connected electrochemical cells 12, are free of electrical fuses.

[0058] Therefore, neither the parallel connectors 14 need to be designed to have a current-carrying capacity that allows a current flow to trigger a fuse in the serial connector 22 or one of the strands 24, 26 or 28, nor do the serial connectors 22 need to be designed to have a current-carrying capacity that allows a current flow to trigger a fuse in the parallel connector 14.

[0059] By eliminating electrical fuses and switching components for creating the parallel and series current paths, the power loss of the energy storage device 10 is reduced and the reliability of the energy storage device 10 is increased, as the risk of component-related failures is minimized.

[0060] Fig. Figure 2 shows selected parts of a first embodiment of the energy storage device 10 in a perspective view. To improve clarity, only three electrochemical cells 12 are shown. It is understood that more than three electrochemical cells 12 are usually present, analogous to the schematic representation in [reference missing]. Fig. 1.

[0061] In this embodiment, the electrochemical cells 12 are in the form of cylindrical cells, each having an upper end face 34, a lower end face 36 opposite the upper end face 34 and a lateral surface 38 connecting the upper end face 34 with the lower end face 36.

[0062] The electrochemical cells 12 are received in a cell holder 40, namely in receiving holders 42, each of which is shaped complementary to the outer contour of the electrochemical cells 12.

[0063] The mounting brackets 42 have projections 44 onto which the lower end face 36 of the respective electrochemical cell 12 inserted into the mounting bracket 42 is placed in a radial edge region. In this way, the respective electrochemical cell 12 is held within the cell holder 40 and at the same time a cooling channel 46 is formed between the lower end face 36 and a cell holder base plate 47.

[0064] The cooling channel 46 can be used to guide a cooling fluid, for example air or a coolant, along the lower end face 36 of the electrochemical cells 12 in order to cool the electrochemical cells 12.

[0065] The cell holder 40 serves both to align and secure the electrochemical cells 12 within the energy storage device 10. It is also possible that an adhesive is provided in the area of ​​the projections 44 with which the electrochemical cells 12 are fixed in their respective assigned mounting holders 42.

[0066] Additionally or alternatively, a thermal paste and / or insulation may be provided, in particular between the cell holder 40 and the electrochemical cells 12, to adjust the thermal behavior of the electrochemical cells 12 within the energy storage device 10.

[0067] Within the respective strands 24 to 28 (of which in Fig. (2 only the first strand 24 and the second strand 26 are indicated) the electrochemical cells 12 are electrically connected to each other via the serial connectors 22.

[0068] As in Fig. As can be seen in Figure 2, the serial connectors 22 are attached to the upper end face 34 of the respective electrochemical cells 12, wherein a first end 48 of the serial connector 22 is contacted with a cell contact 49 of the electrochemical cell 12 of one of the logic cells 16 and a second end 50 is contacted with the housing of the electrochemical cell 12 on its upper end face 34.

[0069] The electrochemical cells 12 within each of the logic cells 16 are electrically contacted with each other via parallel connectors 14, which are attached to the cladding surfaces 38 of the respective electrochemical cells 12.

[0070] Because the serial connectors 22 and the parallel connectors 14 can be attached to different surfaces of the electrochemical cells 12, the energy storage device 10 has a minimized installation space requirement, especially with regard to the available installation space in the area of ​​the upper end faces 34. In addition, flexible design options are available with regard to the arrangement of the serial connectors 22 and parallel connectors 14 on the electrochemical cells 12.

[0071] In the first embodiment, the parallel connectors 14 are formed from a connecting element 51 made of metal, for example steel, aluminum or copper, which is attached to the outer surfaces 38 via the material 19 of medium electrical conductivity, wherein the material 19 is a filled adhesive.

[0072] In Fig. Figure 2 shows the material 19, which has medium electrical conductivity, projecting beyond the connecting element 51. This is only for the sake of clarity in understanding the design of the first embodiment. It is understood that the material 19, which has medium electrical conductivity, can also be completely covered by the connecting element 51.

[0073] Material 19 comprises a matrix of an electrically non-conductive material and a conductivity modifier of an electrically conductive material distributed in the matrix.

[0074] For example, in the first embodiment, the matrix consists of a polyurethane or an epoxy resin in which the conductivity modifier is incorporated.

[0075] In particular, an electrically conductive material is used as a conductivity modifier, selected from the group consisting of carbon, soot, carbon nanotubes, metal particles and combinations thereof.

[0076] Fig. Figure 3 shows selected parts of a second embodiment of the energy storage device 10 according to the invention.

[0077] The second embodiment is essentially identical to the first, so only the differences will be discussed below. Identical or functionally equivalent components are designated with the same reference numeral, and reference is made to the embodiments described above.

[0078] In the second embodiment, the parallel connectors 14 themselves serve as cell holders 40. In other words, the parallel connectors 14 fulfill a dual function, establishing both the electrical connection between the electrochemical cells 12 of the respective logic cell 16 and contributing to the alignment and fixation of the electrochemical cells 12 within the energy storage device 10.

[0079] In Fig. In the second embodiment, the strands 24 and 26 and the logic cells 16 are rotated by 90° compared to the first embodiment, since the logic cells 16 in the second embodiment run along a longitudinal extension direction L of the cell holder 40, which also represents the parallel connector 14, and the strands 24, 26, etc. of the serially connected electrochemical cells 12 run perpendicular to the longitudinal extension direction L.

[0080] Furthermore, the electrochemical cells 12 within each of the strands 24, 26 etc. are electrically connected via the serial connectors 22, which are attached to the upper end face 34 of the respective electrochemical cells 12.

[0081] Thus, the parallel connectors 14 and the serial connectors 22 are again attached to different surfaces of the electrochemical cells 12, namely to different end faces.

[0082] The parallel connectors 14 contact the electrochemical cells 12 via contact sections 52, which also include the projections 44 on which the lower end face 36 of the electrochemical cells rests.

[0083] The contact sections 52 are electrically connected to each other via a conductive section 54. The contact sections 52 and the conductive sections 54 can be made of the same or different materials, wherein at least the contact sections 52 are made of material 19 of medium electrical conductivity and thus determine the minimum and maximum current flow via the parallel connector 14. The conductive section 54 can accordingly have the same or a higher electrical conductivity than the contact sections 52.

[0084] In the second embodiment, the entire parallel connector 14, and thus the entire cell holder 40, is made of the material 19 of medium electrical conductivity, which is a filled plastic.

[0085] This means that the matrix of the medium conductivity material 19 consists of a conventional electrically non-conductive plastic in which the conductivity modifier is distributed.

[0086] For example, material 19 with medium conductivity is PEDOT: PSS.

[0087] Naturally, any other plastics can also be used, which can be adjusted to the desired electrical conductivity by adding the conductivity modifier.

[0088] Fig. Figure 4 shows a sectional view perpendicular to the longitudinal direction L of a third embodiment of the energy storage device 10.

[0089] The third embodiment is essentially identical to the second embodiment, so only the differences will be discussed below. Identical or functionally equivalent components are designated with the same reference numeral, and reference is made to the embodiments described above.

[0090] In the third embodiment, the parallel connector 14, which also serves as a cell holder 40, is designed in multiple parts, namely two parts. This means that the cell holder 40 is composed of a first cell holder half 56 and a second cell holder half 58.

[0091] In Fig. Figure 4 shows, for clarity, the first cell holder half 56, which is assigned to one of the two electrochemical cells 12 shown, spaced apart from it, while the first cell holder half 56, which is assigned to the other of the two electrochemical cells 12 shown, is shown in its mounting position.

[0092] In the assembly position, the outer surface 38 of the respective electrochemical cell 12 is electrically contacted via contact sections 52, analogous to the second embodiment, wherein both the first cell holder half 56 and the second cell holder half 58 each have a contact section 52.

[0093] In the third embodiment, both the first cell holder half 56 and the second cell holder half 58 are made entirely of the material 19 of medium electrical conductivity, in particular of a filled plastic.

[0094] The two cell holder halves 56 and 58 can be fixed to each other by means of a connecting element, for example by means of an adhesive.

[0095] The multi-part design of the parallel connector 14 increases the resistance of the parallel connector 14 to mechanical loads, especially to shear loads.

[0096] Fig. Figure 5 shows a sectional view perpendicular to the longitudinal direction L of a fourth embodiment of the energy storage device 10.

[0097] The fourth embodiment essentially corresponds to the second and third embodiments, so only the differences will be discussed below. Identical or functionally equivalent components are designated with the same reference numeral, and reference is made to the embodiments described above.

[0098] In the fourth embodiment, the parallel connector 14 is again designed in multiple parts.

[0099] The fourth embodiment differs from the third embodiment in that only the contact sections 52 are formed from the material 19 of medium electrical conductivity, while the remaining parallel connector 14 is made of a different material, wherein at least the conductive sections 54, optionally the entire remaining parallel connector 14, can consist of a material with the same or higher electrical conductivity.

[0100] The contact section 52 is in particular a filled adhesive or a filled lacquer. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] Xia et al.: „Review on applications of PEDOTs and PEDOT:PSS in perovskite solar cells“ (Journal of Materials Science: Materials in Electronics (2021), 32:12746-12757, doi: 10.1007 / s10854-020-03473-w

[0022] Alig et al: „Filler Networks of Carbon Allotropes of Different Shapes and Dimensions in a Polymer Matrix“ (Advances in Dielectrics. Springer, Cham, 2022, doi: 10.1007 / 978-3-030-89723-9_10

[0027] Alig et al: „Establishment, morphology and properties of carbon nanotube networks in polymer melts“ (Polymer 53 (2012), S. 4-28, doi: 10.1016 / j.polymer.2011.10.063

[0027]

Claims

[1] Energy storage device (10) comprising a plurality of electrically connected electrochemical cells (12), of which at least two electrochemical cells (12) are connected in parallel by means of a parallel connector (14), wherein the parallel connector (14) comprises a material (19) of medium electrical conductivity comprising a matrix of electrically non-conductive material and a conductivity modifier of an electrically conductive material distributed in the matrix. [2] Energy storage device (10) according to claim 1, wherein the material (19) of medium electrical conductivity has an electrical resistance in the range of 1 to 1000 Ω, preferably in the range of 1 to 100 Ω, more preferably greater than 1 to 10 Ω. [3] Energy storage device (10) according to claim 1 or 2, wherein the material (19) of medium electrical conductivity is a filled plastic. [4] Energy storage device according to claim 1 or 2, wherein the material (19) of medium electrical conductivity is a filled lacquer or a filled adhesive. [5] Energy storage device (10) according to one of the preceding claims, wherein the electrically conductive material is selected from the group consisting of carbon, soot, carbon nanotubes, metal particles and combinations thereof. [6] Energy storage device (10) according to one of the preceding claims, wherein the parallel connector (14) is contacted with a lateral surface (38) and / or an end face (34, 36) of the respective electrochemical cells (12). [7] Energy storage device (10) according to one of the preceding claims, wherein the parallel connector (14) is at the same time a cell holder (40) for the electrochemical cells (12) connected in parallel by the parallel connector (14). [8] Energy storage device (10) according to one of the preceding claims, wherein the parallel connector (14) comprises contact sections (52) and a conductive section (54) connecting the contact sections (52), wherein the contact sections (52) are in direct contact with the electrochemical cells (12) connected by the parallel connector (14), and wherein at least the contact sections (52) consist of the material (19) of medium electrical conductivity. [9] Energy storage device (10) according to one of the preceding claims, wherein the parallel connector (14) is multi-part, in particular two-part. [10] Parallel connector (14) for an energy storage device (10) comprising a plurality of electrically connected electrochemical cells (12), wherein the parallel connector (14) comprises a material (19) of medium electrical conductivity comprising a matrix of electrically non-conductive material and a conductivity modifier of an electrically conductive material distributed in the matrix.

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