DE102021204659A1 - High-voltage battery system - Google Patents

Abstract

The invention relates to a high-voltage battery system with a plurality of lithium-ion battery cells (5) electrically connected to one another, each cell housing containing active material with an electrolyte liquid. According to the invention, the high-voltage battery system (1) has an electrolyte circuit (E) in which the battery cells (5) are fluidically integrated, so that an electrolyte flow is created by means of a negative pressure source and/or a positive pressure source (7; 15, 19). between battery cells (5) is enabled.

Description

The invention relates to a high-voltage battery system with a plurality of lithium-ion battery cells electrically connected to one another according to the preamble of claim 1.

The cell housings of the battery cells of a generic high-voltage battery system each contain active material, consisting of stacked layers of a cathode, an anode and a separator, and an electrolyte liquid. The electrolyte liquid ensures the ion transport between the electrodes of the active material.

A conventional battery cell is filled with electrolyte liquid during the manufacturing process. Since the battery cell is a closed system, the electrolyte liquid remains in the cell housing throughout the battery cell's service life. The battery cell is subject to the following degradation processes during the charging/discharging process. Electrolyte components thus decompose during the period of operation. This increases the viscosity of the electrolyte liquid while at the same time reducing the electrolyte liquid that is still free-flowing (dry out), which is associated with performance losses in the lithium-ion battery cell. Although the active material remains functional due to this drying-out effect, the battery cell capacity is reduced rapidly. In addition, gassing occurs during battery cell operation due to the decomposition of the electrolyte. Furthermore, the electrolyte liquid is subject to an aging process, specifically due to the decomposition of electrolyte components over the battery cell service life. This reduces the shelf life and available life of the battery.

In the prior art, the electrolyte breakdown process is inhibited by the following measures: The composition of the electrolyte liquid can be adjusted accordingly in order to reduce the electrolyte breakdown process. In addition, the electrode surface can be subjected to a special surface treatment. Furthermore, the operating conditions can be adjusted, for example a reduced cut-off voltage can be used. In addition, an excess of electrolyte liquid can be added to the battery cell during the filling process. The same applies to the outgassing process and the aging process.

From the US 2020/0189401 A1 an electrolyte station and an electrolyte power management system are known. From the U.S. 2018/0342753 A1 an electrolytic solution tank for a battery system is known. From the US 2018/0102577 A1 a metal-air battery for a vehicle is known.

All of the measures known from the prior art for inhibiting the degradation process of the electrolyte liquid are accompanied by a production-related complex and costly adjustment of the electrolyte composition and a reduction in the energy density in the battery cell.

The object of the invention is to provide a high-voltage battery system with a plurality of lithium-ion battery cells in which the service life of the cells can be increased and performance losses reduced in a simple manner compared to the prior art.

The object is solved by the features of claim 1. Preferred developments of the invention are disclosed in the dependent claims.

The invention is based on a high-voltage battery system with a plurality of lithium-ion battery cells that are electrically connected to one another. The cell housings contain active material with electrolyte liquid. In order to increase the service life and reduce the loss of performance of the battery cells, the high-voltage battery system has an electrolyte circuit in which the battery cells are fluidically integrated. In this way, an electrolyte flow can be provided between the battery cells by means of a negative pressure source and/or a positive pressure source. As a result, depending on the activation of the electrolyte circuit by means of a control device (for example battery management system), a circulation process, an emptying process and/or a filling process can be implemented. During the circulation process, the electrolyte liquid is circulated in the electrolyte circuit, which increases the service life of the cells and reduces performance losses. In this case, for example, the concentration of electrolyte breakdown products in a battery cell in which there is potentially an excess of breakdown products can be diluted with even fresher electrolyte from other battery cells in which there is a comparatively lower electrolyte concentration.

Alternatively and/or additionally, used electrolyte liquid is drained from the electrolyte circuit in the emptying process. Simultaneously or with a time delay, new electrolyte liquid is fed into the electrolyte circuit during the filling process.

There may be a degradation process in the electrolyte liquid in the cell housing come. Such a degradation process leads to dehydration in the long term. Such dehydration can be prevented by adding and/or exchanging electrolytes.

A core of the invention is therefore that the electrolyte liquid is conveyed through the cell system in an electrolyte circuit by means of at least one pump. From time to time, new electrolyte may be added to the system from a tank/reservoir containing make-up electrolyte. This helps to counteract the "drying out" of the cells. The tank can be topped up with fresh top-up electrolyte from outside the battery application. A second tank can store old electrolyte.

The pump is powered by the tank and can automatically pump electrolyte through the system when needed (determined by battery management system). By using tanks, the time between (tank) refills (from the outside) can be increased. It may even be possible to avoid refilling from the outside if the tanks are large enough.

Aged electrolyte can be replaced with fresh electrolyte. The fresh electrolyte can have a special composition, but can also have a conventional composition.

Unlike the initial (complex) electrolyte, which favors the formation of electrolyte/electrode interfaces/interphases and therefore must contain a certain amount and number of additives, the replenisher electrolyte can serve different purposes thereof.

The refill electrolyte can also be used to reactivate aged cells, for example by having a lower viscosity. Therefore, the make-up electrolyte can have a different composition than the starting electrolyte. Optionally, the top-up electrolyte may contain only a small amount of additives (compared to the initial electrolyte) and have a lower viscosity.

The top-up electrolyte can help extend the cell's cycle life by (partially) replacing the initial electrolyte (which contains certain film-forming additives). The replenisher electrolyte may therefore contain HF reducing additives. The replenisher electrolyte can also help extend the cell's cycle life by replacing degraded electrolyte and thereby rewetting the (partially) dried cell. With this in mind, the refill electrolyte can be a component that can be sold as “after sales”.

The electrolyte can be exchanged in several ways: The initial electrolyte can either be partially replaced by diluting it with refill electrolyte, by rinsing and refilling, or by suction and refilling. In addition, a vent valve can be connected to the system to vent (produced) gas.

The tank must be filled airtight, i.e. without air contact with the electrolyte. This process can be performed by a customer and/or a service representative at an electrolyte filling station or workshop.

The pump can be placed anywhere in the system. When placed behind the tank, it can top up the system with the top-up electrolyte provided by the tank. A vacuum can be applied to drain the system of electrolyte. Gas can also be removed by applying a vacuum when replacing the electrolyte.

The above extraction option has the following additional advantages: If the cells are to be stored, i.e. before second-life use, the electrolyte can be extracted from the cells by applying a vacuum. The aging process is inhibited in cells without electrolyte.

In a further embodiment variant, the system consists of two independent pipe systems, namely one for new electrolyte to be filled in and one for old/aged electrolyte that is to be removed. With both pipe systems, the connection to the cell can contain a valve. By means of the valves, the electrolyte can only be replaced in selected cells (e.g. those with poor performance). The systems can be connected to a tank and/or waste electrolyte container for use during battery operation - alternatively the electrolyte circuit can be connected to them only during maintenance in a workshop.

In an alternative embodiment, the system can be connected in the (geodesically) upper part to a tank containing fresh electrolyte and in the (geodesically) lower part to a tank that serves as a sink for the old electrolyte. With such a configuration, gravity can aid in the electrolyte exchange of the electrolyte in the cells. With both pipe systems, the connection to the cell can contain a valve. The valves would allow the electrolyte to be replaced only in selected cells (e.g. those with poor performance).

Airtight electrolyte filling can be achieved, for example, by inlet and outlet ports that can be evacuated and purged with an inert gas, or by gas-tight electrolyte injection.

Different tank systems can be associated with the electrolyte circuit: For example, the tank system can have a reservoir for fresh electrolyte, which is connected to the pipe system and placed anywhere outside the battery system, but within the application that uses the energy storage system (for example a vehicle). Alternatively, the tank system may include a fresh electrolyte reservoir that is connected to the piping system but placed anywhere within the battery system and within the application.

The invention is particularly suitable for a cell-to-pack or cell-to-car approach. Preferably the cells have a volume of 300 cm ³ up to 2000 cm ³ . This reduces the number of cells and thus also the number of tubes required. The size of the battery system can be between 40 kWh and 150 kWh, for example. The amount of electrolyte in the electrolyte circuit can be between 20 kg and 180 kg, for example.

The entrance and exit (or inlet and outlet) of the cell may be on opposite sides of the cell, respectively. Preferably, the inlet is on the top of the cell and the outlet is on the bottom of the cell (top and bottom represent spatial orientation in the vehicle). With this design, gravity supports the exchange of the electrolyte, so that no pressure or only a low pressure has to be applied for the exchange of the electrolyte. The inlet and outlet can have valves that ensure that the cells can be fluidly connected for a draining process and for a filling process at the same time or independently of time.

The flow cross section at the inlet can be smaller than the flow cross section at the outlet. The inputs and outputs are characterized in that they can ensure the flow of electrolyte into or out of the cell, preferably unidirectionally. In addition, the entrance can be designed in such a way that the inflowing electrolyte has quick access to the electrode/separator combination.

The tube system of the electrolyte circuit can consist mainly of metal, preferably stainless steel or aluminum. Connecting tubes can connect the rows of cells. Furthermore, the entire system can be connected to one another via connecting pipes.

All cells can be identical (reduces the number of parts). The cells can have a capacity between 50 Ah and 250 Ah. The cells are implemented as Li-ion cells, which can also contain metallic lithium as an anode.

The battery system of the vehicle can also have a suitable sensor system that detects aging of the electrolyte. This can be done by sensors within the cell (e.g. pH sensors, reference electrodes) or sensors within the battery management system (measurement of the remaining cell capacities (State of Health (SoH) or the internal resistance). If the sensors detect aging of the electrolyte, an outflow system of the electrolyte circuit, the old electrolyte can be removed (by means of negative pressure or gravity).With the inflow system, new electrolyte can be added at the same time or at different times, for example by means of overpressure, which is created by a pump on the way from the tank to the cells is built.

Adding the new electrolyte and removing the aged electrolyte is done through an inlet and an outlet. These can, for example, be connected to suitable filling and suction systems in a workshop or the like. The inlet or outlet can be connected to the filling/extraction system using gas-tight coupling systems.

Aspects of the invention are described again in detail below: In a technical implementation, a reservoir for new electrolyte liquid and a reservoir for old electrolyte liquid can be assigned to the electrolyte circuit. The battery cells can be integrated, for example, in a parallel connection and/or in a series connection in the electrolyte circuit. Each battery cell can have at least one liquid connection with which the battery cell can be connected to the electrolyte circuit.

Each of the battery cells can preferably have an inlet connection and an outlet connection.

In a preferred embodiment variant, the electrolyte circuit can be divided into an inflow line system and an outflow line system. The inlet connections of the battery cells can be connected to the inlet piping system, while the outlet connections of the battery cells are connected to the outlet piping system could be. A check valve that can be actuated by an electronic control unit can be assigned to the inlet connection and/or the outlet connection of the respective battery cell. The control device can use sensors and/or an algorithm to determine a filling/emptying requirement. Depending on the filling/emptying requirements, the components involved in the electrolyte circuit, i.e. check valves, overpressure source, vacuum source, can be controlled.

In a specific embodiment variant, an overpressure source, ie a pressure pump, can be assigned to the inflow line system. A pressure relief valve can be assigned to the drain line system. In this case, if pressure builds up during a filling process (due to the overpressure source), the pressure relief valve can open once a pressure threshold value has been reached, as a result of which the used electrolyte liquid can be drained via the drain line system. The pressure relief valve can also double as a pressure relief valve in the event of a thermal event, opening to provide pressure relief.

It is preferred if the emptying process is carried out under the action of gravity. For this purpose, in the design position of the respective battery cell, the inlet connection can be arranged geodetically at the top, while the outlet connection of the battery cell is arranged geodetically at the bottom.

In an alternative embodiment variant, the overpressure source can be omitted in the inflow line system and only a reservoir for new electrolyte liquid can be arranged. In contrast, a negative pressure source and a reservoir for used electrolyte liquid can be arranged in the drain line system. In this case, when the suction pump is operating, the old electrolyte liquid is sucked out of the battery cells and at the same time new electrolyte liquid is sucked into the battery cells.

The components of the electrolyte circuit, i.e. negative pressure and/or positive pressure source and shut-off valves, used electrolyte reservoir and new electrolyte reservoir can be directly components of the high-voltage battery system that is installed in the vehicle, for example. For example, the used electrolyte reservoir can be emptied externally at a vehicle customer service and the new electrolyte reservoir can be filled at the same time.

Alternatively, the components of the electrolyte circuit, namely in particular the overpressure source, underpressure source and used electrolyte reservoir and new electrolyte reservoir can be external components that are outside the system limits of the battery system, i.e. are not part of the high-voltage battery system. In this case, the high-voltage battery system can have connection points to which the above external components can be detachably connected, for example in vehicle customer service.

• 1 bis 7 jeweils unterschiedliche Ausführungsbeispiele eines Hochvolt-Batteriesystems mit Elektrolyt-Kreislauf; und
• 8 bis 12 jeweils Detailansichten zur strömungstechnischen Verschaltung von Batteriezellen.

Exemplary embodiments of the invention are described below with reference to the accompanying figures. Show it:

• 1 until 7 in each case different exemplary embodiments of a high-voltage battery system with an electrolyte circuit; and
• 8th until 12 detailed views of the fluidic interconnection of battery cells.

In the 1 a high-voltage battery system is indicated to the extent necessary for understanding the invention. The high-voltage battery system 1 has in the 1 example, a total of twelve battery modules 3. The high-voltage battery system 1 can be built into an electrically operated vehicle. In the 1 For example, the battery modules 3 are arranged in pairs one behind the other in the vehicle longitudinal direction x. Each battery module 3 has, for example, a total of six battery cells 5 which are stacked one behind the other in the vehicle transverse direction y.

In the 1 the battery cells 5 are, for example, prismatic cells with a component-rigid, cuboid cell housing in which the active battery material, consisting of cathode, anode and separator, with electrolyte liquid is located. The high-voltage battery system 1 has in the 1 in addition, an electrolyte circuit E, in which all battery cells 5 are fluidically integrated. In the 1 the battery cells 5 installed in the high-voltage battery system 1 are connected in series in the electrolyte circuit E, for example. The electrolyte circuit E also has a flow pump 7, which can be controlled via a vehicle-internal control unit 9, such as the battery management system. When the flow pump 7 is in operation, a circulation process takes place, in which the electrolyte liquid in the electrolyte circuit E is circulated. This results in an electrolyte flow between the battery cells 5. Due to the electrolyte flow, an electrolyte exchange between the battery cells 5 takes place. This reduces degradation processes in the electrolyte liquid located in the respective battery cells 5 .

In the in the 2 All battery cells 5 are also connected in series one behind the other in the electrolyte circuit E. In contrast to 1 points in the 2 the electrolyte circuit E has an inlet line system 11 and an outlet line system 13 . The feed line system 11 is made up of a pressure pump 15 and a reservoir 17 for new electrolyte liquid. The drain line system 13 is made up of a suction pump 19 and a reservoir 21 for used electrolyte liquid. In an emptying process, used electrolyte liquid is pumped from the battery cells 5 into the reservoir 21 for used electrolyte liquid by means of the suction pump 19 . A filling process, in which the pressure pump 15 pumps new electrolyte liquid into the battery cells 5, can take place with a time delay or at the same time.

In the 2 For example, both the inlet line system 11 and the outlet line system 13 are not integral components of the high-voltage battery system 1, but rather are positioned outside the system limits. The two systems 11 , 13 are detachably coupled to the electrolyte circuit E of the high-voltage battery system 1 at connection points 23 , 25 . In contrast to 1 the two pumps 15, 19 are controlled by means of a vehicle-external control unit 9, for example in the case of a vehicle customer service case in a vehicle workshop.

In the 3 a high-voltage battery system 1 is shown, the basic structure of which 2 equals. In contrast to 2 points in the 3 the drain line system 13 does not have a suction pump 19, but rather a pressure relief valve 29.

During a filling process, the pressure pump 15 of the inflow line system 11 is activated, as a result of which pressure builds up in the electrolyte circuit E. Once a pressure threshold value has been reached, the pressure-limiting valve 29 opens so that the used electrolyte liquid flows out into the reservoir 21 for used electrolyte liquid. In the 3 For example, both the inlet line system 11 and the outlet line system 13 are not integral components of the high-voltage battery system 1, but rather are positioned outside the system limits. The two systems 11 , 13 are detachably coupled to the electrolyte circuit E of the high-voltage battery system 1 at connection points 23 , 25 . The two pumps 15, 19 can - as well as in the 2 - Be controlled by means of a vehicle-external control unit 9. Irrespective of this, in all exemplary embodiments of the invention, the control unit 9 can be implemented in a suitable manner either as an on-board control unit or as an off-board control unit.

That in the 4 shown embodiment is similar to the basic structure 2 . In contrast to 2 is in the 4 in the supply line system 11, the pressure pump 15 omitted. During an emptying process, the suction pump 19 of the drain line system 13 is activated, so that used electrolyte liquid is sucked into the reservoir 21 . At the same time, new electrolyte liquid is sucked into the electrolyte circuit E from the reservoir 17 .

In the in the 5 The embodiment shown is no longer all battery cells 5 connected in series in the electrolyte circuit E, but rather the battery cells 5 are arranged in parallel, as is shown in FIG 6 is indicated. In the 6 each of the battery cells 5 has an inlet connection 31 on the top side and an outlet connection 33 on the bottom side. A check valve 35 is assigned to each inlet port 31 , while a check valve 37 is assigned to each outlet port 33 . The check valves 35, 37 can be controlled via the control unit 9, that is, they can be opened or closed depending on the filling/emptying requirement.

In the 6 the inlet line system 11 has a main line 39 which leads from the new electrolyte reservoir 17 to a branch point 41 . The pressure pump 15 is arranged in the main line 39 . The main line 39 branches at the branch point 41 into a total of six sub-lines 43, for example. These are each connected to the inlet connections 31 of the battery cells 5 . The check valve 35 is positioned in each of the sub-lines 43 . In the same way, the drain line system 13 also has a main line 45 in which the suction pump 19 is arranged. The main line 45 branches off at a branch point 46 into a total of six sub-lines 47 , for example, which are each connected to the outlet connections 33 of the battery cells 5 . The check valve 37 is arranged in each of the partial lines 47 .

In the 7 1 shows a high-voltage battery system 1 with an electrolyte circuit E, which has a main line 49 running in the vehicle longitudinal direction x and arranged centrally in the vehicle transverse direction y. This extends into the 7 between an inlet connection point 23 and an outlet connection point 25, which can be coupled to an external inlet and/or outlet line system 11, 13 in the event of an electrolyte exchange. Branching off from the main line 49 in the vehicle transverse direction y are sub-lines 51 which are fluidically connected to the battery cells 5 . It should be emphasized that the invention is not limited to this special course of the main and partial lines 49, 51. Rather, any other suitable courses of the main and partial lines 49, 51 are covered by the invention. For example, the spatial directions x and y compared to 7 be swapped with each other.

In the 8th a battery cell 5 with a liquid connection 53 is indicated in a detailed view. A liquid inlet or a liquid outlet can take place via the liquid connection 53 . In contrast, takes place in the 9 the liquid inlet or the liquid outlet no longer via a common liquid connection 53, but via separate inlet and outlet connections 31, 33. The inlet and outlet connections 31, 33 are in FIG 9 positioned on the top of the cell. Alternatively, in the 10 the inlet port 31 is positioned at the cell top, while the outlet port 33 is positioned at the cell bottom.

In the 11 four battery cells 5 positioned one behind the other in the stacking direction are shown in an exploded view by way of example. The battery cells 5 each have plug-in connections 55 on their upper side, via which the battery cells 5 can be fluidically connected to one another. In the same way, the battery cells 5 are provided with plug-in connections 55 on the bottom side, via which the battery cells 5 can be fluidically connected to one another on the bottom side.

In the 12 Another embodiment is shown in an exploded view, which is essentially the 11 is equivalent to. In contrast to 11 the battery cells 5 only have plug-in connections 55 on their upper sides, but not on their bottom sides.

Reference List

1

High-voltage battery system

3

battery modules

5

battery cells

7

flow pump

9

battery management system

11

inlet pipe system

13

drain pipe system

15

pressure pump

17

Reservoir for new electrolyte liquid

19

suction pump

21

Reservoir for used electrolyte fluid

23, 25

connection points

27

control unit

29

pressure relief valve

31

inlet connection

33

outlet connection

35, 37

check valves

39

main line

41

branch point

43

partial lines

45

main line

47

partial lines

49

main line

51

partial lines

53

liquid connection

55

plug connectors

E

electrolyte circuit

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US 2020/0189401 A1 [0005]
• US 2018/0342753 A1 [0005]
• US 2018/0102577 A1 [0005]

Claims (12)

High-voltage battery system with a plurality of lithium-ion battery cells (5) electrically connected to one another, in each of whose cell housings active material with electrolyte liquid is located, characterized in that the high-voltage battery system (1) has an electrolyte circuit (E), in in which the battery cells (5) are fluidically integrated, so that an electrolyte flow between battery cells (5) is made possible by means of a negative pressure source and/or a positive pressure source (7; 15, 19), specifically for a circulation process in which the electrolyte Liquid in the electrolyte circuit (E) can be circulated, or for an emptying process in which old electrolyte liquid can be removed from the electrolyte circuit (E), or for a filling process in which new electrolyte liquid is poured into the electrolyte circuit (E) can be fed. high-voltage battery system claim 1 , characterized in that the electrolyte circuit (E) is assigned a reservoir (17) for new electrolyte liquid and/or a reservoir (21) for old electrolyte liquid is assigned. high-voltage battery system claim 1 or 2 , characterized in that the battery cells (5) are arranged in parallel and/or in series in the electrolyte circuit (E). High-voltage battery system according to one of the preceding claims, characterized in that each battery cell (5) has at least one liquid connection (53) for connection to the electrolyte circuit (E), in particular an inlet connection (31) and an outlet connection (33). high-voltage battery system claim 4 , characterized in that the electrolyte circuit (E) is divided into an inflow line system (11) and an outflow line system (13), and that via the inflow line system (11) new electrolyte liquid into the electrolyte circuit ( E) can be fed in and old electrolyte liquid can be removed from the electrolyte circuit (E) via the drain line system (13), and/or that in particular the inlet connections (31) of the battery cells (5) on the inlet line system (11 ) are connected and/or the outlet connections (33) of the battery cells (5) are connected to the drain line system (13). high-voltage battery system claim 4 or 5 , characterized in that the inlet connection (31) and / or the outlet connection (33) of the respective battery cell (5) from a control unit (9) controllable check valve (35, 37) is assigned, depending on the filling / emptying requirement is open or closable. High-voltage battery system based on one of the Claims 5 or 6 , characterized in that the inlet line system (11) is assigned an overpressure source (15) and the outlet line system (13) is assigned a pressure relief valve (29), and that the pressure relief valve (29), in particular when pressure builds up during a filling process , opens when a pressure threshold value is reached, as a result of which used electrolyte liquid can be discharged into the used electrolyte reservoir (21), and/or that in particular the pressure-limiting valve (29) acts as a pressure relief valve in the event of a thermal event, which opens to relieve pressure. High-voltage battery system based on one of the Claims 4 until 7 , characterized in that in the design position of the respective battery cell (5), the inlet connection (31) is arranged geodetically at the top and the outlet connection (33) is arranged geodetically at the bottom. High-voltage battery system according to one of the preceding claims, characterized in that the overpressure and/or underpressure source (7; 15, 19) and/or the old electrolyte reservoir (21) and the new electrolyte reservoir (17) are components of the high-voltage battery system (1) installed in a vehicle, for example, and that in particular the used electrolyte reservoir (21) and/or the new electrolyte reservoir (17) can be emptied or filled externally in a customer service case. High-voltage battery system based on one of the Claims 1 until 8th , characterized in that the overpressure and / or vacuum source (7; 5, 19) and the old electrolyte reservoir (21) and the new electrolyte reservoir (17) are external components, that is not part of the high-voltage battery system (1) and that in particular the electrolyte circuit (E) has connection points (23, 25) to which the external components can be detachably coupled in the event of customer service. High-voltage battery system according to one of the preceding claims, characterized in that the electrolyte circuit (E) is assigned at least one sensor which detects a current battery cell parameter, and that in particular the control unit (9) on the basis of the current battery cell parameter carries out a circulation process, an emptying process and/or a filling process. High-voltage battery system according to one of the preceding claims, characterized indicates that the new electrolyte liquid fed into the electrolyte circuit (E) in a filling process has a special composition, and that in particular the composition of the new electrolyte liquid is different from the original composition of the old electrolyte liquid.

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