Electrochemical system, and method for operating an electrochemical system

Abstract

The invention relates to an electrochemical system (1), in particular a battery system, to be assigned a first cell stack (3), which comprises a plurality of liquid electrolyte cells (5), and a second cell stack (2, 4), which comprises a plurality of solid electrolyte cells (6). The electrochemical system (1) operates with a combined fluid-operated heat transport system (9) that exchanges heat via solid bodies and is designed to transport heat between the various cell stacks (2, 3, 4).

Description

[0001] Electrochemical system and method for operating an electrochemical system

[0002] The invention relates to an electrochemical system, in particular a battery system, comprising a plurality of electrochemical cells arranged in stacks. The invention further relates to a method for operating such an electrochemical system.

[0003] US patent 2013 / 0244061 A1 discloses a battery system, specifically an electrochemical system, designed for use in electric and hybrid vehicles. Various battery components of the system according to US patent 2013 / 0244061 A1 are said to differ from one another with respect to their electrochemistry. Lithium-ion batteries and nickel-metal hydride batteries are mentioned as possible battery types. Furthermore, US patent 2013 / 0244061 A1 lists flywheel energy storage devices and capacitors as potential energy storage devices.

[0004] Other energy storage devices, which include both lithium batteries and capacitors, are described, for example, in documents CN 106696721 A and CN 110034611 A.

[0005] A battery system disclosed in CN 108598598 A is constructed as a lithium battery, distinguishing between different cells. In CN 108598598 A, particular attention is paid to the heat generation in the different cells during charging and discharging processes and also to heat transport, with the aim of combining a high energy density with a high performance of the battery system.

[0006] WO 2023 / 208279 A2 concerns an electrochemical cell, in particular an electrolysis cell, and a method for manufacturing a component of an electrochemical cell. The component is an open-porous sintered body through which flow-conducting channels of defined geometry are formed.

[0007] The invention is based on the objective of further developing electrochemical systems, for example battery systems, compared to the prior art, particularly with regard to thermal aspects.

[0008] This problem is solved according to the invention by an electrochemical system with the features of claim 1. Likewise, the problem is solved by a method for operating an electrochemical system designed according to claim 9. The embodiments and advantages of the invention explained below in connection with the operating method also apply mutatis mutandis to the device, i.e., the electrochemical system, in particular in the form of a stacked battery system, and vice versa.

[0009] The electrochemical system described in the application comprises a first cell stack consisting of a plurality of liquid electrolyte cells. Additionally, the electrochemical system comprises a second cell stack consisting of a plurality of solid electrolyte cells. The number of different types of cell stacks, i.e., cell stacks consisting of liquid electrolyte cells as well as cell stacks consisting of solid electrolyte cells, is not subject to any theoretical limitations. In any case, a heat transfer system exists, which is designed to transport heat between the different types of cell stacks. This heat transfer system is operated with a fluid, in particular in liquid form, and simultaneously exchanges heat between the cell stacks via at least one solid.

[0010] The combined solid-based heat transfer between the different cell stacks, via a fluid (i.e., a liquid and / or a gas), allows for particularly effective and material-friendly absorption of geometric changes that occur during charging and discharging processes. Charging and discharging currents, as well as heat flows, can be tailored to the cell chemistry, which varies depending on the cell stack.

[0011] The invention is based on the premise that solid-state electrolyte cells (SSCs) have a low charge acceptance at low temperatures compared to other cell types, meaning they can only be charged with low currents. Only at higher temperatures do SSCs exhibit a high charge acceptance, which is particularly desirable for charging electric vehicles. In contrast, liquid electrolyte cells have a significantly higher charge acceptance at low temperatures, but require earlier current limiting as temperatures rise. Both SSCs and liquid electrolyte cells are used in mechanically braced cell stacks, taking into account that SSCs with a metallic anode exhibit greater volume expansion during charging than liquid electrolyte cells.

[0012] Against the background of these considerations, the patented method for operating an electrochemical system, comprising a first cell stack with a plurality of liquid electrolyte cells and a second cell stack with a plurality of solid electrolyte cells, provides that heat is transported between the cell stacks by means of a heat transfer medium in the form of a fluid and simultaneously via at least one solid. In this process, the fluid flows, in particular, through a channel formed between individual liquid electrolyte cells, wherein the aforementioned solid, i.e., the heat conductor, engages at least partially in the channel and is simultaneously connected to the cell stack formed from solid electrolyte cells in a thermally conductive manner. Flowing through the latter cell stack with the fluid is not required.In contrast, the free space between the various cell stacks can be traversed by the fluid circulating in a cooling circuit. When the electrochemical system, composed of several cell stacks, is configured as a battery system, it is also referred to as a multi-chemistry battery. Depending on various possible configurations, the heat transfer system of the stacked electrochemical system includes a solid, three-dimensionally structured heat conductor, which is thermally coupled to both the liquid electrolyte cells and the solid electrolyte cells. In particular, this heat conductor can be located, at least partially, within the aforementioned channel. In principle, known forming, shaping, and machining processes are suitable for producing the three-dimensional structure of the heat conductor.Depending on the materials, cell chemistry, and operating conditions, components of the electrochemical system, including the heat conductor, can be coated. The separation of different compartments within the electrochemical system is possible in a known manner using metallic or non-metallic seals. This applies particularly to seals of the heat transfer system.

[0013] If the three-dimensionally structured heat conductor is arranged between adjacent liquid electrolyte cells, it can include a base piece oriented orthogonally to the aforementioned channel, which thermally contacts a plurality of solid electrolyte cells. The heat conductor, including the base piece, is made of metal and can be constructed in one or more parts.

[0014] Regardless of the precise design of the heat transfer system, the electrochemical system can comprise three or more adjacent cell stacks of identical height, with one stack of liquid electrolyte cells positioned between two stacks of solid electrolyte cells. The solid heat conductor can be thermally connected to only one of the adjacent cell stacks, particularly a stack of solid electrolyte cells, via a base of the aforementioned type. This provides particularly good conditions for compensating for thermally induced dimensional changes.If one considers stacked solids, especially in three-dimensionally structured form, each arranged between two liquid electrolyte cells, these solids can be thermally connected in the stacking direction alternately with a first solid electrolyte cell stack, which is arranged on a first side next to the liquid electrolyte cell stack, and a second solid electrolyte cell stack, which is located on the opposite side of the liquid electrolyte cell stack.

[0015] The three-dimensionally structured heat conductor can, in particular, be expanded metal. Regarding the production and geometric characteristics of expanded metal, reference is made to DE 10 2022 112 175 B3 as an example. In the present case, a grid designed as expanded metal, which is part of a plate arrangement for an electrochemical cell disclosed in DE 10 2022 112 175 B3, can be placed between two liquid electrolyte cells and is characterized by planar contact with adjacent surfaces. Instead of a single grid designed as expanded metal, two such grids can also be inserted into the channel formed between two liquid electrolyte cells, with those sides of the grids that have the most surface areas lying in a common plane being brought into thermally conductive contact with the surfaces of the liquid electrolyte cells.In contrast, relatively sharp-edged sides of the grids can be placed on top of each other.

[0016] Another grid arrangement, not necessarily made of expanded metal, suitable for installation between two liquid electrolyte cells, consists of two grids, essentially mirror images of each other, each formed from a sheet of metal that rests against one of the two liquid electrolyte cells over a large area. Numerous tabs are formed by stamping; these protrude from the sheet and are supported by the second sheet.

[0017] An alternative grid arrangement consists of a single sheet metal component positioned in a plane located centrally between the surfaces of adjacent liquid electrolyte cells. In this case, tongues formed from the sheet metal project outwards from this plane on both sides, bearing against one or the other adjacent liquid electrolyte cell. Compared to the grid arrangement formed from a pair of sheets, this arrangement results in smaller contact areas with the surfaces of the liquid electrolyte cells, while achieving particularly high elastic compliance. Regardless of whether a three-dimensionally structured, planar heat conductor inserted between two cells is constructed as a single unit or in multiple parts, the heat conductor can have several elastic tongues that provide it with elastic compliance in the stacking direction of the cells.

[0018] Two exemplary embodiments of the invention are explained in more detail below with reference to a drawing. This drawing shows:

[0019] Fig. 1 shows a partial first embodiment of a stacked electrochemical system with a fluid-conducting and solid-supported heat transport system,

[0020] Fig. 2 shows another electrochemical system designed as a battery system in a representation analogous to Fig. 1.

[0021] Fig. 3 shows the electrochemical system, composed of several cell stacks, according to Fig. 1 in an overview cross-sectional view.

[0022] Unless otherwise stated, the following explanations refer to both embodiments. Corresponding or essentially equivalent parts are marked with the same reference numerals in all figures.

[0023] An electrochemical system, designated by reference numeral 1, is configured as a battery system consisting of three cell stacks 2, 3, and 4. The cells 5 of cell stack 3, located between cell stacks 2 and 4, are liquid electrolyte cells 5. Cell stacks 2 and 4, located on either side of cell stack 3, are solid electrolyte cells 6. All cell stacks 2, 3, and 4, also referred to as stacks, are clamped between end plates 7 and 8. Any reference in this text to components of the electrical system 1 being arranged one above the other or side by side refers only to the arrangements shown in Figures 1 to 3 and does not imply any statement about the actual spatial orientation of these components.

[0024] The entire electrochemical system 1 is used as a rechargeable traction battery in an electric vehicle. A heat transfer system 9, comprising a cooling circuit 10, is provided for demand-based temperature control depending on the cell type. The term "cooling circuit" is used for simplicity regardless of whether components of the electrochemical system 1 are to be cooled or heated. In any case, the heat transfer system 9, which includes the cooling circuit 10, is capable of transporting heat between the various cell stacks 2, 3, 4.

[0025] A coolant reservoir – more precisely, a container holding a fluid intended for heat transport – as well as fittings and a pump that circulates the fluid used for temperature control are not shown. Likewise, Figures 1 to 3 do not show temperature sensors that detect temperatures within the electrochemical system 1, nor do they show means for data transmission and processing.

[0026] The solid electrolyte cells 6, which form the two cell stacks 2, 4, are stacked directly on top of each other, as can be seen in Figure 3. In contrast, the liquid electrolyte cells 5 of the middle cell stack 3 are spaced parallel to each other, so that a channel 11 for the fluid used as a heat transfer medium is formed between each pair of liquid electrolyte cells 5. A heat conductor 12, 13 is inserted into the channel 11, which in the case of Figure 3 has the shape shown in Figure 1. The heat conductor 13 sketched in Figure 2 is also suitable for installation in the electrochemical system 1 according to Figure 3.

[0027] In the embodiment shown in Figures 1 and 3, the heat conductor 12 is largely constructed from two half-sheets 14, 15. Each half-sheet 14, 15 has a flat base sheet 16 from which tongues 17 protrude on one side. The tongues 17 are formed. The recesses created in the base sheet 16 by the formation of the tongues 17 are not shown in the figures. Each tongue 17, which is part of one half-sheet 14, 15, rests on the other half-sheet 15, 14. Both base sheets 16 make contact over a large area with one of the liquid electrolyte cells 5.

[0028] In the embodiment shown in Figure 2, the heat conductor 13, unlike the design shown in Figure 1, is made from a single piece of sheet metal. Here, the base plate 16, i.e., the largest part of the originally completely flat sheet, is located centrally between the adjacent liquid electrolyte cells 5. The liquid electrolyte cells 5 are contacted exclusively by the tongues 17 projecting from both sides of the base plate 16. In this case as well, the base plate 16 has recesses resulting from the shape of the tongues 17.

[0029] In both the embodiment shown in Figures 1 and 3 and in the embodiment shown in Figure 2, each heat conductor 12, 13 has a connection section 18 projecting laterally beyond the stack 3. A base 19, also belonging to the heat conductor 12, 13, connects to the connection section 18 and makes contact with two adjacent solid electrolyte cells 6. Furthermore, parts of the solid electrolyte cells 6 are also exposed to the fluid flowing in the cooling circuit 10. In these cases, the cooling circuit 10 is implemented as immersion cooling. This means that a dielectric, electrically insulating fluid is used as the flowing fluid, which makes contact with electrically conductive parts of the components to be cooled, in this case, the various cells 5, 6.

[0030] Assuming that the various cell stacks 2, 3, 4 are to be charged at a low starting temperature, the charging process begins with the charging of the liquid electrolyte cells 5 forming cell stack 3. This quickly generates waste heat, which is used to heat the solid electrolyte cells 6. This results in a heat flow both through the heat conductors 12, 13 and through the flowing fluid. The heat transfer system 9 thus transfers heat both via solids and through a flowing, in particular liquid, medium. The heating of the solid electrolyte cells 6 by the heat generated during the charging of the liquid electrolyte cells 5 contributes significantly to the fact that the solid electrolyte cells 6 quickly reach a temperature that enables rapid charging.

[0031] Another method for temperature control of the electrochemical system 1 is used when the charging process begins at a high starting temperature. In this case, the focus is initially on charging the solid electrolyte cells 6, while the liquid electrolyte cells 5 are cooled or thermally homogenized using the cooling circuit 10.

[0032] In any case, an increasing state of charge of the solid electrolyte cells 6 can cause them to expand, which can also increase the distance between the mutually prestressed end plates 7, 8. The elastically designed heat conductors 12, 13 compensate for these geometric changes, with the increased cross-sectional area of ​​the channels 11 contributing to an increased heat transfer performance of the heat transport system 9. Thus, good conditions are provided for continuing a fast charging process with increasing cooling capacity. The heat transport system 9 can be used not only during the charging process but also during the discharging of the electrochemical system 1, i.e., the battery system.

[0033] List of reference symbols for the electrochemical system

[0034] Stack of solid electrolyte cells

[0035] Stack of liquid electrolyte cells

[0036] Stack of solid electrolyte cells

[0037] Liquid electrolyte cell

[0038] Solid electrolyte cell

[0039] End plate

[0040] End plate

[0041] Heat transfer system

[0042] Cooling circuit

[0043] channel

[0044] Heat conductor

[0045] Heat conductor

[0046] half-sheet

[0047] half-sheet

[0048] base plate

[0049] Tongue

[0050] Connection section

[0051] foot piece

Claims

Patent claims 1. Electrochemical system (1) comprising a first cell stack (3) comprising a plurality of liquid electrolyte cells (5) and a second cell stack (2, 4) comprising a plurality of solid electrolyte cells (6), and a combined fluid-operated and heat-transferring solid heat transfer system (9) designed to transfer heat between the different cell stacks (2, 3, 4).

2. Electrochemical system (1 ) according to claim 1 , characterized in that the heat transport system (9) comprises a solid, three-dimensionally structured heat conductor (12, 13) which is thermally coupled to several liquid electrolyte cells (5) as well as to several solid electrolyte cells (6).

3. Electrochemical system (1 ) according to claim 2, characterized in that the heat conductor (12, 13) is arranged at least partially between adjacent liquid electrolyte cells (5) in a channel (11 ) of the heat transport system (9) provided for conveying a fluid.

4. Electrochemical system (1 ) according to claim 3, characterized in that the heat conductor (12, 13) comprises a foot piece (19) oriented orthogonally to the said channel (11 ) which thermally contacts a plurality of solid electrolyte cells (6).

5. Electrochemical system (1 ) according to one of claims 1 to 4, characterized in that it comprises at least three cell stacks (2, 3, 4) arranged side by side of equal height, wherein a cell stack (3) of liquid electrolyte cells (5) is arranged between two cell stacks (2, 4) of solid electrolyte cells (6).

6. Electrochemical system (1 ) according to claims 4 and 5, characterized in that the heat conductor (12, 13) is thermally connected only to one of the adjacent cell stacks (2, 4) via a foot piece (19) of the type mentioned.

7. Electrochemical system (1 ) according to one of claims 2 to 6, characterized in that the three-dimensionally structured heat conductor (12, 13) is designed as expanded metal.

8. Electrochemical system (1) according to any one of claims 2 to 7, characterized in that the three-dimensionally structured heat conductor (12, 13) has several elastic tongues (17), making it flexible in the stacking direction of the cell stacks (2, 3, 4).

9. Method for operating an electrochemical system (1) comprising a first cell stack (3) with a plurality of liquid electrolyte cells (5) and a second cell stack (2, 4) with a plurality of solid electrolyte cells (6), wherein heat is transported between the cell stacks (2, 3, 4) by means of a heat transfer medium present as a fluid and simultaneously via at least one solid (12, 13).

10. Method according to claim 9, characterized in that the fluid flows through a channel (11) which is formed between individual liquid electrolyte cells (5) and in which the said solid body (12, 13) engages.

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