DE102015003122A1 - Motor vehicle with a battery assembly and method for operating a battery assembly - Google Patents

Abstract

Motor vehicle (1) with a battery arrangement (2), comprising a lead-acid battery (9) whose negative electrode (18) is connected to a ground potential (7), and a lithium-ion battery (10), whose positive electrode (19) is connected to the positive electrode (17) of the lead-acid battery (9) and whose open circuit voltage in the fully charged state is greater than the charging voltage of the lead-acid battery (9), wherein at least one consumer (3, 4, 5) of the motor vehicle (1) to the Battery arrangement (2) is connected, wherein the battery assembly (2) further energy storage (11) whose negative electrode (22) is connected to the ground potential (7), and a switching device (12) by means of which the negative electrode (20) the lithium-ion battery (10) upon the occurrence of at least one of one or more connection events to a positive electrode (21) of the further energy store (11) and at least one of one or more downshift event sen against the ground potential (7) is switchable.

Description

The invention relates to a motor vehicle with a battery assembly, comprising a lead-acid battery whose negative electrode is connected to a ground potential, and a lithium-ion battery whose positive electrode is connected to the positive electrode of the lead-acid battery and the open-circuit voltage in the fully charged state greater than the charging voltage of the lead-acid battery is, wherein at least one consumer of the motor vehicle is connected to the battery assembly. In addition, the invention relates to a method for operating a battery assembly of a motor vehicle.

Modern vehicles have an increasing number of consumers, such. As belt starter generators or turbochargers, which require high currents of up to several hundred amps in a very short time. Likewise, new recuperation methods are increasingly used in motor vehicles, which entails an increase in charging and discharging cycles. Conventional lead acid batteries do not meet the requirements of these technologies.

There are therefore known battery arrangements comprising a lead-acid battery with a parallel-connected lithium-ion battery, wherein the open-circuit voltage of the lithium-ion battery in the fully charged state is greater than the charging voltage of the lead-acid battery. This ensures that the lithium-ion battery is only partially charged when the lead-acid battery is almost fully charged. In the case of a voltage increase by recuperation, the charge acceptance of the lithium-ion battery is thus much higher than that of the lead-acid battery.

The DE 10 2012 007 575 B3 discloses an energy storage device having at least one plurality of lead-based memory cells having first energy storage and a parallel to this switchable second energy storage, which formed from a combination of different based on lithium, lithium titanate, lithium-iron-phosphorus or a nickel-metal hydride compound memory cells is. In addition, a capacitor, in particular a double-layer capacitor, can be connected in series with the memory cells.

However, since lithium-ion batteries exhibit a large increase in internal resistance at low outside temperatures, conventional battery arrangements have the disadvantage that their performance is heavily dependent on external environmental conditions at high load requirements.

The invention is therefore based on the object to provide an improved motor vehicle with a battery assembly that can be reliably used in a larger number of operating cases.

According to the invention, this object is achieved in a motor vehicle of the type mentioned above in that the battery arrangement comprises a further energy store whose negative electrode is connected to the ground potential, and a switching device by means of which the negative electrode of the lithium-ion battery at least one is switchable from one or more Zuschaltereignissen to a positive electrode of the further energy storage and at the occurrence of at least one of one or more switch-back events against the ground potential.

The invention is based on the consideration, the voltage of the lead-acid battery connected in parallel, the lithium-ion battery comprehensive circuit branch, as needed, to increase. For this purpose, the further energy store is connected in series with the lithium-ion battery as a function of at least one switch-on event, so that their voltages add up. Similarly, in at least one downshift event, in the simplest case so the elimination of the Zuschaltereignisses, the battery assembly can be restored to its original state, so that only the lithium-ion battery and the lead-acid battery are connected in parallel.

For the described switching tasks, the switching device is provided, which may have a mechanical switch, but preferably has a known per se from the prior art arrangement of multiple power semiconductor switch. In addition, it is particularly expedient if the switching device comprises a control device which is designed to detect the occurrence of switch-on events and switch-back events and to control the switch elements.

The connection events and the switch-back events are selected so that they cover operating conditions in which an increased output voltage of the lithium-ion battery is required. This may in particular relate to cases in which due to a low outside temperature, in particular below freezing, the internal resistance of the lithium-ion battery has increased so much that when high currents are discharged, a significant voltage dip occurs at its positive electrode. Operational cases to be suitably selected will be described in more detail below.

Advantageously, with a vehicle according to the invention an operation of particularly electricity-intensive consumers in a large number of operating conditions are made possible. These operating conditions must be detected only by suitable sensors and detected by the control device. By connecting the further energy storage so particular temperature-induced voltage dips of the lithium-ion battery can be compensated or at least mitigated, so that even in these cases a short-term load on the lead-acid battery and an associated cyclization is prevented.

A preferred embodiment provides that a connection event is a falling below a first Spannungsschwellwertes and / or a reset event is exceeded, in particular greater than the first voltage threshold selected, second voltage threshold by the voltage at the positive electrode of the lead-acid battery. It is therefore proposed to detect the voltage at the positive electrode of the lead-acid battery and to detect a turn-on event from a drop below a first voltage threshold value. It can thus indirectly detected the internal resistance of the battery assembly and be switched on the increase of the further energy storage. Analogously thereto, exceeding a second voltage threshold value is rated as a downshift event, wherein it is particularly expedient to select the second voltage threshold value above the first voltage threshold value, so that a hysteresis behavior is achieved which prevents oscillation between the switch-on event and the switch-back event. Of course, the voltage at the positive electrode of the lead-acid battery can also be derived from other voltages, in particular those at the positive electrode of the lithium-ion battery or at other locations of an electrical system of the motor vehicle, which are electrically connected to the positive electrode of the lead-acid battery , Advantageously, these embodiments thus cover all cases in which the voltage at the positive electrode of the lead-acid battery falls below a critical level, namely the first voltage threshold, and is treated by connecting the further energy store.

It can also be provided in a motor vehicle according to the invention that a connection event exceeding a first current threshold and / or a switch-off event falls below a, selected in particular smaller than the first current threshold, second current threshold by the output from the battery assembly to the consumers connected to them stream has. Thus, alternatively or additionally, it may also be provided that the current intensity which is provided by the battery arrangement indicates the necessity of connecting the further energy store, while the first current threshold value is exceeded. It is therefore concluded via a low external resistance of the battery assembly that the voltage applied to the load voltage should be increased. Similarly, a downshift event can be triggered when the second current threshold value is undershot. In this case, the first current threshold value can be identical to the second current threshold value, but it is preferred that the second current threshold value is selected smaller than the first current threshold value in order to realize a hysteresis behavior as explained with respect to the voltage threshold value.

It is further advantageous in a motor vehicle according to the invention if a connection event is the activation and / or a switch-back event the deactivation of at least one consumer, in particular a turbocharger and / or a starter generator. It is thus used in particular switching on and / or off the consumer for the connection of the other energy storage. As consumers, in particular those come into consideration, the short term record a very high power of the battery assembly, such as turbocharger or starter generators, especially belt starter generators. Since in modern motor vehicles, the operating state, including the activation and / or deactivation of consumers, often as information on a vehicle bus system is ready, so advantageously the need for connecting the other energy storage can be easily detected.

It is particularly advantageous in such a motor vehicle when the operating voltage of the further energy store provided for the time of its connection is selected to be greater than a voltage dip which occurs at the time the consumer is switched on at the positive electrode of the lead battery. It is therefore expedient, in the case of known consumers, to design that via the no-load voltage of the further energy store so that the voltage drop caused by them is at least compensated.

The dimensioning of the further energy storage also depends on the voltage of the electrical system. In the case of a 12 V vehicle electrical system, it is therefore particularly advantageous if the further energy store is designed to provide a voltage between 1.0 and 3.7 V, preferably between 1.5 and 3.0 V, during connection. It is particularly useful if it has a nominal capacity of at least 2500 Ås, preferably 3500 Ås. It is also particularly advantageous if the further energy store is designed such that, starting from a charged state in a respective configuration of the battery arrangement, its operating voltage after delivery of a charge of up to 2000 As, preferably up to 2700 As, without intermediate Reloading is reduced by a maximum of 1.0V. Advantageously, voltage drops can thus be compensated without renewed intermediate charging in the case of several switch-on events (for example three times switching on for 3 s each with an average current output of 300 A).

It is particularly advantageous in a motor vehicle according to the invention if the further energy store is a further lithium-ion battery. In this case, those lithium-ion battery, whose negative electrode is switchable to a positive electrode of this further lithium-ion battery and against the ground potential, also be referred to as the first lithium-ion battery. It is preferred if the further lithium-ion battery comprises exactly one lithium-ion cell. In particular, in the case of 12 V electrical systems, the provision of precisely one lithium-ion cell will cause a suitable increase in the voltage at the positive electrode of the lithium-ion battery. Such a choice is also expedient in particular if the level of the expected current consumption of a consumer is unknown. Advantageously, in a 12-volt vehicle electrical system, the on-board network voltage is thus increased by 1.0 to 3.7 V, preferably by 1.0 to 3.0 V, when the additional lithium-ion battery is connected, so that a large number of load cases can be compensated. Alternatively or additionally, it can be provided that the further lithium-ion battery is formed from at least one lithium titanate cell. Such prior art lithium ion cells typically have a cell voltage of 2.2V, and are therefore particularly suitable for use with the battery assembly. Of course, the former lithium-ion battery may include at least one lithium titanate cell.

As an alternative to a further lithium-ion battery, the further energy store can advantageously be a supercapacitor, in particular a double-layer capacitor, a pseudo-capacitor or a hybrid capacitor formed from such capacitors. Such capacitors are characterized in that they can store large amounts of charge. In the case of a 12 V on-board network, it is expedient for the supercapacitor to have a rated voltage between 1.5 and 3.0 V and / or a capacity of at least 1000 F. It is particularly preferred if the capacitance is at least 2500 F, so that with a fully charged supercapacitor high currents (eg of the order of magnitude of 300 A) can be provided several times in succession at a sufficient voltage, without the supercapacitor again completely to have to recharge. When operating a 24 V vehicle electrical system, these values must of course be adapted.

It is furthermore expedient in a motor vehicle according to the invention if a connection event is the drop in at least one temperature, in particular the ambient temperature of the motor vehicle and / or a temperature detected at one of the batteries, below a temperature threshold value. It is preferred in this case if the temperature is detected directly at the lithium-ion battery by means of a sensor in order to be able to react directly to the temperature-specific changes in the operating parameters by connecting the further energy store. It is further preferred if a temperature threshold value is used as a connection event in addition to one of the connection events already described. Thus, the behavior of the battery arrangement can be adapted even more accurately to ambient conditions with advantage.

In addition, it is advantageously provided in a motor vehicle according to the invention that the battery arrangement comprises at least one DC-DC converter, which is designed to provide a charging power for the further energy storage. Since the further energy store typically has a lower operating voltage than the lithium-ion battery, the DC-DC converter must be provided in order to supply the further energy store with a charging power with an adapted converted charging voltage. Conveniently, the DC-DC converter is the input side connected to the positive electrode of the lead-acid battery or the positive electrode of the lithium-ion battery, so that it can reduce their voltage to the required charging voltage of the other energy storage. The DC-DC converter can in particular have a rated power between 30 and 80 W, preferably between 45 and 55 W.

Furthermore, it is of particular advantage in the motor vehicle according to the invention if the battery arrangement, in particular its DC-DC converter, is designed to charge the further energy store at a low temperature of the lithium-ion battery up to a higher voltage than at a higher temperature of the lithium battery. ion battery. It is therefore proposed to make the voltage up to which the further energy storage is charged dependent on the temperature of the lithium-ion battery. It is particularly preferred if the further energy storage is a supercapacitor. Since at low temperatures, the internal resistance of the lithium-ion battery increases, it is particularly advantageous if the switched further energy storage in such a case also provides a higher additional voltage for compensation. For this purpose, the controller can evaluate a detected temperature of the lithium-ion battery and the Charging the other energy storage, in particular by means of the DC-DC converter, control.

Finally, in a motor vehicle according to the invention, it is particularly advantageous if the switching device is designed to galvanically separate the lithium-ion battery from the ground potential when at least one of one or more disconnection events occurs. The switching device has for this purpose a further switching state in which the lithium-ion battery is disconnected from the ground potential. As a separation event in particular for the lithium-ion battery inadmissible over and / or undervoltage is considered, which can lead to permanent damage to the lithium-ion battery. Advantageously, a safety functionality that is normally required anyway for the lithium-ion battery is simultaneously realized by the switching device.

In addition, the invention relates to a method for operating a battery assembly of a motor vehicle, wherein the battery assembly is a lead-acid battery whose negative electrode is connected to a ground potential, and a lithium-ion battery whose positive electrode connected to the positive electrode of the lead-acid battery and whose open circuit voltage in fully charged state is greater than the charging voltage of the lead-acid battery, comprises and at least one consumer of the motor vehicle is connected to the battery assembly, the battery assembly comprises a further energy storage, the negative electrode is connected to the ground potential, and a switching device, by means of which the negative electrode the lithium-ion battery upon the occurrence of at least one of one or more Zuschaltereignissen to the positive electrode of the further energy storage and upon the occurrence of at least one of one or more switch-back events against the Massep otential is switched.

All embodiments of the motor vehicle according to the invention can be analogously transferred to the inventive method, so that even with these already mentioned advantages can be achieved.

Further advantages and details of the invention will become apparent from the embodiments described below and from the drawings. Showing:

1 A first embodiment of a motor vehicle according to the invention with a battery assembly,

2 a curve of the voltage at a positive electrode of a lead acid battery in 1 the battery arrangement shown and the current delivered to the consumers connected to them over time, wherein voltage thresholds are used as Zuschaltereignisse, and

3 a curve of the voltage at the positive electrode of the lead-acid battery of 1 shown battery arrangement and the output to the consumers connected to them power over time, the activation and deactivation of a consumer are used as Zuschaltereignisse.

1 is a schematic diagram of a first embodiment of a motor vehicle 1 comprising a battery assembly 2 , three consumers 3 . 4 . 5 and a bus system 6 ,

The consumer 3 is there as an electric turbocharger and the consumer 4 designed as a starter generator, both via the bus system 6 are controllable and exchange operating information with this. The consumer 5 is exemplary of others in the motor vehicle 1 existing consumers. The consumers 3 . 4 . 5 are at a ground potential 7 of the motor vehicle 1 connected.

The battery arrangement 2 has a clamp 8th to which consumers 3 . 4 . 5 are connected, as well as a lead acid battery 9 , a lithium-ion battery 10 , another energy storage 11 , a switching device 12 and a DC-DC converter 13 on. Next to it are a voltmeter 14 , a power meter 15 and a temperature sensor 16 intended.

The lead battery 9 is a conventional lead-acid battery with a fully charged open-circuit voltage of about 12.6 V. A positive electrode 17 the lead-acid battery 9 is about the ammeter 15 with the clamp 8th and a negative electrode 18 the lead-acid battery 9 with the ground potential 7 connected. Parallel to the lead acid battery 9 is the voltmeter 14 arranged.

The lithium-ion battery 10 includes six lithium titanate cells to give a fully charged open circuit voltage of about 13.2V. Alternatively, it may also be formed of four lithium-nickel-manganese-cobalt oxide cells with a total voltage of 14.4V. A positive electrode 19 the lithium-ion battery 10 is with the positive electrode 17 the lead-acid battery 9 and a negative electrode 20 the lithium-ion battery 10 with the switching device 12 connected. The temperature sensor 16 is the lithium-ion battery 10 assigned and designed to detect their operating temperature.

The further energy storage 11 is another lithium-ion battery and includes one Lithium titanate cell with a fully charged open circuit voltage of about 2.2 V with a rated capacity of 2500 As. He has a connection of his positive electrode 21 with the switching device 12 on while his negative electrode 22 against the ground potential 7 is switched.

The switching device 12 includes a switch 23 and a controller 24 , The desk 23 has a common contact 25 that with the negative electrode 20 the lithium-ion battery 10 is connected, and a first switching contact 26 that with the positive electrode 21 the further energy storage 11 is connected. A second switching contact 27 is at ground potential 7 whereas a third switch contact 28 idles. The desk 23 is realized with a known from the prior art circuit of power semiconductor devices and is by the controller 24 controlled. This receives input signals of the bus system 6 , the voltmeter 14 , the current measuring device 15 and the temperature sensor 16 ,

The DC-DC converter 13 is at his entrance 29 with the positive electrode 19 the lithium-ion battery 10 and at its exits 30 with the positive electrode 21 and the negative electrode 22 the further energy storage 11 connected. Its reference potential is the ground potential 7 , He converts those at his entrance 29 applied voltage of about 13.2 V in a charging voltage for the other energy storage 11 and has a nominal power of 50W.

In a normal operating case, the switch 23 with the second switching contact 27 connected so that the lead acid battery 9 parallel to the lithium-ion battery 10 with the clamp 8th connected is. The further energy storage 11 is via the DC-DC converter 13 merely charged, that is, the positive electrode 21 is with no other component of the battery assembly 2 or of the motor vehicle 1 connected. If, for example, recuperation of electrical energy into the battery arrangement occurs in this operating state 2 , so first is the lithium-ion battery 10 charged because they have a lower charging resistance than the lead acid battery 9 having. Because the lithium-ion battery 10 for a significantly higher number of charging and discharging cycles than the lead-acid battery 9 is designed, the lead-acid battery 9 so spared and can reach a longer service life.

If it comes from this operating case to a connection of a very high load, here an example of activation of the turbocharger 3 , so it sinks with the voltmeter 14 detected voltage between the positive electrode 17 the lead-acid battery and its negative electrode 18 , This is caused by the voltage drop across the internal resistance of the parallel connected lead-acid battery 9 and the lithium-ion battery 10 , This voltage drop can be so strong, especially at very low temperatures, that consumers 4 . 5 can no longer receive a sufficient operating voltage and errors can occur. The entire electrical system of the motor vehicle 1 can thus become unstable.

The time course of such an operating case is in 2 which is a diagram and on the vertical axis of which a voltage U and a current I are plotted over time t. The solid lines show the voltage measurement device 14 detected voltage 31 and the power meter 15 recorded electricity 32 , Next to it are a first voltage threshold 33 and a second voltage threshold 34 as well as a switch-on time 35 and a switch-off time 36 of the turbocharger 3 entered. Before the switch-on time 35 shows the tension 31 a value of 13.2 V, which corresponds to the usual operating case when the switch 23 at the second switch contact 27 is applied. At the switch-on time 35 it comes as described to a burglary of tension 31 below the first voltage threshold 33 , which is chosen here as 12.0V. The control device 24 now recognizes the achievement of the first voltage threshold 33 and turns on the switch 23 to the first switch contact 26 , so now the lithium-ion battery 10 with the further energy storage 11 connected in series parallel to the lead acid battery 9 lies. The voltage 31 increases accordingly to the voltage of the other energy storage 11 ,

Because the electricity 32 after the switch-on time 35 decreases, the voltage drop across the internal resistance decreases, so that at a time 37 the second voltage threshold 34 is reached. Since this is defined as a downshift event, the switch becomes 33 back to the second switch contact 37 by means of the control device 24 connected. This is the negative electrode 20 the lithium-ion battery 10 again at ground potential 7 at. The voltage 31 then falls to a value above the first voltage threshold 33 and only rises at the switch-off time 36 back to the value of 13.2 volts. At this time, the electricity is falling 32 also off again. A dashed line shows the course of a voltage 38 which would result if the further energy storage 11 would not be switched or would not be provided. The course of the tension 31 In contrast, advantageously much more stable.

Alternatively or in addition to the voltage thresholds 33 . 34 can also be a first current threshold 39 and a second current threshold 40 be set, wherein the control device 24 when the first current threshold is exceeded 39 the further energy storage 11 switches on and falls below the second current threshold 40 the negative electrode 20 the lithium-ion battery 10 again against the ground potential 7 on. For this purpose, the control device detects 24 also the voltage meter 15 detected current flowing through the terminal 8th flows.

The switching behavior of the switching device 12 was previously exemplified by the example of the connection of the turbocharger 3 described. Since as Zuschalt- and Rückschaltereignis only from the voltmeter 14 and the power meter 15 detected internal parameters of the battery assembly 2 are used, this switching behavior of the control device results 24 also when connecting any other very high loads, especially in the case of a consumer 5 that is not with the bus system 6 connected is. Will however be the starter generator 4 switched on, which is known to be a high to very high load, this is the bus system 6 detected and by the controller 24 evaluated. This is designed to activate the starter generator 4 to be used as a reconnect event and its deactivation as a downshift event.

This operating case is in 3 shown in the as in 2 a voltage U and a current I are plotted over time t. At the time 35 the belt starter generator is activated, wherein the voltage drop caused by the switching on, that of the voltage measuring device 14 is detected, not the first voltage threshold 33 below. But there alone from the bus system 6 transmitted activation is used as a turn-on, the further energy storage 11 still connected by the switch 33 from the second switch contact 27 to the first switch contact 26 is switched. The voltage 31 thus increases at the time 35 by the amount of voltage of the other energy storage 11 at. At the time 36 becomes the starter generator 4 deactivated, as shown, the current 32 drops again, and the switch 33 again to the second switch contact 27 on. The lithium-ion battery 10 lies with its negative electrode 20 So again at the ground potential and the voltage 31 drops to the voltage of 13.2 volts.

Furthermore, the control device 24 designed to the temperature of the lithium-ion battery 10 by means of the temperature sensor 16 cumulatively to the above-described Zu- or Rückschaltereignis to take into account. As the internal resistance of the lithium-ion battery 10 also depends on their temperature, is a connection of the other energy storage 11 when activating the starter generator 4 not necessary if due to a sufficiently high temperature no unfavorable voltage drop at the terminal 8th is to be expected. This in 3 shown operating behavior is therefore only at the temperature sensor 16 detected temperatures below 5 ° C from the controller 24 causes. Such temperature limits may be within a wide range of possible operating temperatures and are highly dependent on the configuration of the battery assembly 2 determined experimentally or by simulation.

Finally, the control device 24 also with the lithium-ion battery 10 connected to it, that it is able to detect a damaging over- and undervoltage on it. Such operating states are defined as separation events. The control device 24 recognizes them and turns on the switch 23 to the third switch contact 28 , The lithium-ion battery 10 is separated with it and can not be damaged by the present over-tightening or undervoltage.

As part of one of 1 corresponding second embodiment of a motor vehicle 1 is the further energy storage 11 realized as a designed as a hybrid capacitor supercapacitor.

This has a capacity of 2500 F and a rated voltage of 2.2 V, so that the storable charge is about 5500 As. This charge is sufficient when activating a turbocharger 3 which receives on average for a period of 3 s a current of 300 A, a sufficient additional voltage for a lithium-ion battery 10 provide. In addition, even after another similar load case still an additional voltage of about 1.8 V and after a third activation of the turbocharger 3 an additional voltage of about 1.5 V can be provided without the additional energy storage 11 in the meantime, recharge. This will provide an acceptable compensation for the voltage dip caused by the turbocharger 3 arises, reached.

In addition, a DC-DC converter 13 with the control device 24 connected and controlled by her. The controller evaluates 24 that of the temperature sensor 16 detected temperature and gives at low temperatures of the lithium-ion battery 10 a charging voltage of 2.2 V, which falls to 1.8 V with increasing detected temperature.

The remaining embodiments of the first embodiment can be analogously to the second embodiment.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102012007575 B3 [0004]

Claims (13)

Motor vehicle ( 1 ) with a battery arrangement ( 2 ) comprising a lead acid battery ( 9 ), whose negative electrode ( 18 ) with a ground potential ( 7 ), and a lithium-ion battery ( 10 ), whose positive electrode ( 19 ) with the positive electrode ( 17 ) of the lead-acid battery ( 9 ) and their open circuit voltage in the fully charged state is greater than the charging voltage of the lead-acid battery ( 9 ), wherein at least one consumer ( 3 . 4 . 5 ) of the motor vehicle ( 1 ) to the battery assembly ( 2 ), characterized in that the battery arrangement ( 2 ) further energy storage ( 11 ), whose negative electrode ( 22 ) with the ground potential ( 7 ), and a switching device ( 12 ), by means of which the negative electrode ( 20 ) of the lithium-ion battery ( 10 ) upon the occurrence of at least one of one or more turn-on events to a positive electrode ( 21 ) of the further energy store ( 11 ) and at least one of one or more switch-back events against the ground potential ( 7 ) is switchable. Motor vehicle ( 1 ) according to claim 1, characterized in that a connection event falls below a first voltage threshold ( 33 ) and / or a switch-over event exceeding one, in particular greater than the first voltage threshold value ( 33 ), second voltage threshold ( 34 ) by the tension ( 31 ) at the positive electrode ( 17 ) of the lead-acid battery ( 9 ). Motor vehicle ( 1 ) according to claim 1 or 2, characterized in that a connection event exceeds a first current threshold ( 39 ) and / or a downshift event falls below one, in particular smaller than the first current threshold value ( 39 ), second current threshold ( 40 ) by the battery assembly ( 2 ) to the consumers connected to them ( 3 . 4 . 5 ) stream ( 32 ). Motor vehicle ( 1 ) according to one of the preceding claims, characterized in that a switch-on event activating and / or a switch-back event, the deactivation of at least one consumer ( 3 . 4 ), in particular a turbocharger ( 3 ) and / or a starter generator ( 4 ) is. Motor vehicle ( 1 ) according to claim 4, characterized in that the intended for the time of its connection operating voltage of the further energy storage greater than a voltage dip at the time of switching on the consumer ( 3 . 4 ) at the positive electrode ( 17 ) of the lead-acid battery ( 9 ) occurs is selected. Motor vehicle ( 1 ) according to one of the preceding claims, characterized in that the further energy store is a further lithium-ion battery. Motor vehicle ( 1 ) according to one of the preceding claims, characterized in that the further lithium-ion battery ( 11 ) comprises exactly one lithium-ion cell and / or is formed from at least one lithium titanate cell. Motor vehicle ( 1 ) according to one of claims 1 to 5, characterized in that the further energy storage is a supercapacitor, in particular a double-layer capacitor, a pseudo-capacitor or a hybrid capacitor formed from such capacitors. Motor vehicle ( 1 ) according to one of the preceding claims, characterized in that a connection event the decrease of at least one temperature, in particular the ambient temperature of the motor vehicle ( 1 ) and / or one on one of the batteries ( 9 . 10 . 11 ) is below a temperature threshold. Motor vehicle ( 1 ) according to one of the preceding claims, characterized in that the battery arrangement ( 2 ) at least one DC-DC converter ( 13 ), which for providing a charging power for the further energy storage ( 11 ) is trained. Motor vehicle ( 1 ) according to one of the preceding claims, characterized in that the battery arrangement ( 2 ), in particular its DC-DC converter, is adapted to charge the further energy store at a low temperature of the lithium-ion battery up to a higher voltage than at a higher temperature of the lithium-ion battery. Motor vehicle ( 1 ) according to one of the preceding claims, characterized in that the switching device ( 12 ) is adapted to the lithium-ion battery ( 10 ) when at least one of one or more separation events occurs galvanically from the ground potential ( 7 ) to separate. Method for operating a battery arrangement ( 2 ) of a motor vehicle ( 1 ), the battery arrangement ( 2 ) a lead acid battery ( 9 ), whose negative electrode ( 18 ) with a ground potential ( 7 ), and a lithium-ion battery ( 10 ), whose positive electrode ( 19 ) with the positive electrode ( 17 ) of the lead-acid battery ( 9 ) and their open circuit voltage in the fully charged state is greater than the charging voltage of the lead-acid battery ( 9 ) and at least one consumer ( 3 . 4 . 5 ) of the motor vehicle ( 1 ) to the battery assembly ( 2 ) connected, characterized in that the battery arrangement ( 2 ) a further energy store ( 11 ), whose negative electrode with the ground potential ( 7 ), and a switching device ( 12 ), by means of which the negative electrode ( 20 ) of the lithium-ion battery ( 10 ) upon the occurrence of at least one of one or more switch-on events to a positive electrode of the further energy store ( 11 ) and at least one of one or more switch-back events against the ground potential ( 7 ) is switched.

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