EP2781000A1

EP2781000A1 - Storage battery protected from internal short-circuits

Info

Publication number: EP2781000A1
Application number: EP12788499.7A
Authority: EP
Inventors: Sébastien CARCOUET; Bruno Beranger; Daniel Chatroux
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2011-11-17
Filing date: 2012-11-14
Publication date: 2014-09-24
Also published as: US20140354232A1; WO2013072358A1; US10059216B2; FR2982998B1; FR2982998A1

Abstract

The invention relates to a storage battery, comprising at least: first and second stages (Et1, Et2) electrically connected in series, each stage including at least first to third cells (A11, A21, A31) electrically connected in parallel; and at least first and second current limiters (Li11, Li21) via which the first to third cells (A11, A21, A31) of said first stage (Et1) are connected in parallel and via which the first to third cells (A12, A22, A32) of said second stage (Et2) are connected in parallel.

Description

BATTERY OF ACCUMULATORS PROTECTED AGAINST SHORT CIRCUITS

The invention relates to electrochemical storage batteries. These can be used, for example, in the field of electric and hybrid transport or on-board systems.

Hybrid combustion / electric or electric vehicles include in particular high power batteries. Such batteries are used to drive an AC electric motor through an inverter. The voltage levels required for such motors reach several hundred volts, typically of the order of 400 volts. Such batteries also have a high capacity to promote the autonomy of the vehicle in electric mode.

To obtain high powers and capacities, several groups of accumulators are placed in series. The number of stages (number of accumulator groups) and the number of parallel accumulators in each stage vary according to the desired voltage, current, and capacity for the battery. The combination of several accumulators is called a storage battery. The electrochemical accumulators used for such vehicles are generally of the lithium type for their ability to store a significant amount of energy with a weight and a volumetric content. Lithium ion iron phosphate LiFeP04 battery technologies are undergoing significant development due to a high intrinsic safety level, to the detriment of a slightly lower energy storage density. An electrochemical accumulator usually has a nominal voltage of the following order of magnitude:

3.3 V for iron phosphate lithium ion technology, LiFePO4,

4.2 V for a cobalt oxide-based lithium ion technology. The invention can also be applied to supercapacitors.

FIG. 1 represents a Bat ion battery Bat ion known in the state of the art. Bat battery consists of four stages Et1, Et2, Et3 and Et4 connected in series. Each stage has four similar accumulators connected in parallel. The terminals of the accumulators of the same stage are connected together by means of strong electrical connections. Each stage is also connected to the adjacent stages via high section electrical connections in order to pass strong currents corresponding to the sum of the currents of the accumulators of a stage. One or more loads are intended to be connected to the terminals N and P of the battery 1. The voltage across the four stages is noted respectively U 1, U 2, U 3 and U 4. In this diagram, the total voltage U between the terminals N and P of the battery 1 is the sum of the voltages U 1, U 2, U 3 and U 4. The current flowing through each fourth-stage accumulator Et4 is denoted 11, 12, 13 and 14, respectively. The current I generated on the P-terminal of the battery Bat is the sum of the currents 11, 12, 13 and 14. A balance circuit Load balancing Eq is connected to the terminals of each stage of the Bat battery.

Throughout the life of the battery, some faults may appear on some accumulators making up the battery. A fault on an accumulator usually results either by shorting the accumulator, or by an open circuit, or by a large leakage current in the accumulator. It is important to know the impact of a battery failure. Open or short-circuiting can cause an overall launcher failure of the entire battery.

In the case of the appearance of a large leakage current in a battery of a stage, the battery behaves like a resistor which causes a discharge of the accumulators of the stage considered to zero. The risks of starting fire are low because the energy is dissipated relatively slowly. In lithium technology, the discharge of the accumulators of the stage up to a zero voltage deteriorates them implicating their replacement in addition to the initially defective accumulator. When an accumulator forms a short-circuit, the other three accumulators of the stage will initially discharge into this accumulator, because of the strong section of the electrical connections between them. The fuse placed in series with the battery in short circuit will interrupt the parasitic discharge of the other three accumulators.

In order to protect the battery Bat from the consequences of a short circuit in an accumulator, each battery has a fuse connected to it in series. When an accumulator forms a short circuit, the current flowing through it increases substantially and melts its series fuse in order to protect the rest of the battery Bat. In the absence of a fuse, the dissipation of energy in the accumulator in short circuit would induce its heating as well as that of other accumulators discharging. Such dissipation could be the cause of a start of fire. Lithium ion technologies are particularly at risk when a stage has a large number of parallel accumulators to store a large amount of energy. Cobalt oxide is known as a highly reactive chemistry. Iron phosphate is known to him as the safest chemistry. The use of fuses is therefore particularly suitable for these technologies, particularly for iron phosphate which tolerates a certain surge.

However, the presence of fuses in series between the accumulator stages induces non-negligible losses, particularly disabling for on-board applications. WO201 1/003924 discloses a battery structure for eliminating the losses induced by a protection system during normal operation of the battery, and further ensuring continuity of service of the battery when an element battery is in short circuit or circuit breaker.

In this document, the battery comprises at least first and second branches each having at least first and second accumulators connected in series. The battery further comprises a fuse through which the first accumulators are connected in parallel and through which the second accumulators are connected in parallel. The cut-off threshold of the fuse is sized to open when one of the accumulators is short-circuited.

When the battery supplies a vehicle electric motor, its recharging occurs either when the vehicle is stopped by connecting the battery to the electrical network, or during the driving of the vehicle during phases during which the electric motor operates as a generator. During a quick charge when the vehicle is stopped or when the electric motor is running as a generator, it may be possible to apply charge or balancing currents to the accumulators that are not negligible. The fuses connected in parallel connections can thus be traversed by relatively large currents. In addition, some fuses can be crossed by the accumulation of recharging or balancing currents to several accumulators of the same floor and remote recharge connectivity. Some fuses may thus represent a common connection of several accumulators to the balancing circuit. Consequently, the sizing of the fuses of parallel connections may be difficult to ensure both the protection of the accumulators, the continuity of service of the battery during a malfunction of an accumulator, and the recharging of the different cells. Accumulators. Joule losses can also occur during recharging or balancing due to currents flowing through the fuses. The life of the fuses can also be reduced by the repeated application of load currents through them.

The document US2010 / 072950 describes a storage battery including: three stages connected in series;

- three accumulators in parallel in the floors;

respective fuses connected in series with each of the accumulators; transistors associated with respective fuses, applying an alarm signal on a control circuit when the voltage across their fuse crosses a threshold;

connections ensuring the parallel connection of the accumulators of each of the stages. No two-stage common component participates in the parallel connection of the respective accumulators of these two stages.

The fuses have a function of interruption of the current in case of overcurrent. The current flowing through the transistors when they are closed is also negligible compared to the current delivered by the accumulators.

The invention aims to solve one or more of these disadvantages. The invention thus relates to a storage battery as defined in the claims.

The invention also relates to a system defined in the claims.

Other characteristics and advantages of the invention will emerge clearly from the description which is given hereinafter, by way of indication and in no way limitative, with reference to the appended drawings, in which:

FIG 1 is a schematic representation of an example battery according to the state of the art;

FIG. 2 is a schematic representation of an exemplary battery according to one embodiment of the invention;

FIG. 3 illustrates an example of bidirectional current limiter;

FIG. 4 illustrates another example of bidirectional current limiter;

FIG. 5 illustrates yet another example of bidirectional current limiter;

FIG. 6 is a diagram illustrating the usual intensity response of a JFET transistor as a function of the voltage applied between its source and its drain;

FIG. 7 is a schematic representation of an example of a battery according to one embodiment of the invention, having been simulated during the malfunctioning of an electrochemical cell;

FIG. 8 is a diagram illustrating the evolution of the intensity in electrochemical cells of the battery of FIG. 7;

FIG 9 is a diagram illustrating the evolution of the voltage across different electrochemical cells of the battery of Figure 7;

FIG. 10 is a diagram illustrating the evolution of the voltage across electrochemical cells in a stage comprising a faulty electrochemical cell;

FIG. 11 schematically illustrates an advantageous variant of connection of electrochemical cells in a battery stage;

FIG. 12 illustrates a monodirectional current limiter that can be used in the variant of FIG. 11;

FIG. 13 illustrates an isolation circuit of a battery module including a faulty electrochemical cell; FIG. 14 illustrates a battery including several modules in a normal operating mode;

FIG. 1 illustrates the battery of FIG. 14 in an operating mode in which one of the modules includes a faulty electrochemical cell.

Hereinafter, the current imigraph will denote a component or circuit traversed by an increasing current with the voltage at its terminals when this voltage is below a saturation threshold, and traversed by a substantially constant saturation current when this voltage is greater than saturation threshold.

Advantageously, the saturation current is greater than 50% of the maximum value of the current for any voltage across the limit below the saturation threshold. Advantageously, the saturation current is at least equal to the maximum value of the current for a voltage across the lower limit of the saturation threshold.

FIG. 2 is a diagrammatic representation of an exemplary battery 1 according to one embodiment of the invention. The battery 1 comprises five stages Eti to Et5 connected electrically in series. Each stage comprises five accumulators or electrochemical cells electrically connected in parallel. The battery 1 thus comprises five branches Br1 to Br5 electrically connected in parallel. The parallel connection of the accumulators of a stage is carried out via current imagers Li. Each current im Li of the example participates in the parallel connection of two accumulators of one stage. as well as the parallel connection of two accumulators of another stage.

An electric charge 3 is connected to the terminals P and N of the battery 1, so as to be supplied by this battery. A load balancing management circuit 2 is electrically connected to each of the stages Eti to Et5. Circuit 2 is configured to charge the accumulators of these stages. Circuit 2 is also configured to track the state of charge of the accumulators. The circuit 2 is also configured to implement load balancing of the accumulators of these stages, according to the monitoring of their state of charge. The functions of charging / monitoring the state of charge / load balancing are known per se and will not be detailed further. At terminals P and N, the battery 1 advantageously comprises power reader cols traversed by the currents in parallel coming from different branches Br1 to Br5.

The current imitators allow to imitate the current delivered through a short-circuited accumulator, in order to avoid any risk of overheating and fire, even in the presence of a large number of connected accumulators. parallel in each floor. The discharge rate of the accumulators of a stage including a short-circuited accumulator is also imitated, which may make it possible to continue using the battery 1. In addition, an accumulator The short circuit is not isolated from circuit 2, which makes it possible to detect its spike and continue its monitoring. By measuring the voltage at each stage, the circuit can thus detect a spike, by noting, for example, that one stage is discharging or charging differently from the other stages. Since a short-circuited accumulator remains connected in parallel with the other accumulators of the stage, it can be detected that the other accumulators are gradually discharged therein.

The current im litors also make it possible to implement a distribution of intensity between the accumulators of the various branches in the presence of a short-circuited accumulator.

The use of current imagers in the parallel connections of the accumulators makes it possible to apply high load currents to the accumulators, to implement either a fast charge via the electrical network (necessary for to ensure reduced charging times), or a load by an electric motor running as a generator (for example during a braking phase of a vehicle), without inducing inadvertent disconnection of these connections in parallel.

During a charge or discharge phase, the main current in a branch passes through all the accumulators connected in series in this branch. During such operation, if all the accumulators are similar and have the same state of charge or discharge, no transverse current flows through the current liimeters Li. The current limiters Li may be of any suitable type. Figure 3 illustrates an example of the current imager Li based on the use of JFET type transistors. The current limiter Li of this example advantageously comprises two transistors T1 and 12 mounted head to tail. The transistor T1 has its grill connected to its source. Its drain is intended to be connected to a terminal of an accumulator. The transistor T1 thus ensures imitation of the current flowing in the direction al lant of its drain towards its source. The transistor 12 has its grill connected to its source. Its drain is intended to be connected to a terminal of an accumulator. Transistor 12 thus provides an imitation of the current flowing in the direction al lant of its drain towards its source. A JFET type transistor has the advantage of being naturally closed in the absence of a control circuit for polarizing its grill. It is thus not necessary to have a control circuit to allow the passage of cross currents balancing load or recharging accumulators.

The mounting of two transistors upside-down in the current limiter Li makes it possible to achieve a bidirectional current imitation. Thus, a current l imitor Li: imitates the discharge current from an accumulator to which it is connected when it discharges into another short-circuited accumulator;

- Imitates the charge current (from several accumulators) to the accumulator to which it is connected when it is in short circuit.

Figure 6 illustrates a classic example of a transistor characteristic

JFET for a potential difference Vgs between the grid and the given source. The ordinate corresponds to the drain-source current Ids, the abscissa corresponding to the potential difference Vds between its drain and its source.

In a manner known per se, the current Ids is substantially proportional to the voltage Vds when Vds is less than the saturation voltage Vs. The current is substantially constant and close to a saturation current Is when the voltage

Vds is greater than said saturation threshold Vs.

Those skilled in the art will know in a manner known per se determine the dimensioning of the transistors of the current limiters to obtain desired values of saturation current Is and saturation voltage Vs.

In the example illustrated in FIG. 6, the current Ids for a voltage Vds greater than Vs is greater than the current Ids for any voltage Vds less than Vs.

However, it is possible to consider a crawling of the intensity when Vds crosses the value Vs, notably because of the heating of the transistors. However, the current Ids remains significant when Vds is greater than Vs, for example at least equal to 0.5 * Is.

The JFET transistor or transistors of the current imi Li may also be replaced by depletion-type Mosfet transistors whose gate is connected to the source and whose drain is connected to a terminal of an accumulator. Such a transistor can also be naturally closed in the absence of a control circuit to polarize the grill. The JFET transistor (s) of the current imi L can also be replaced by N channel type enrichment-type Mosfet transistors. Such a transistor being in the natural state of being open, its grill must be permanently controlled. to keep it closed.

FIG. 4 shows a first example of a Li-imitator structure that makes it possible to keep two N-channel-type enhancement-type Mosfet transistors in the closed state, without the need for an external control circuit to polarize its grill.

Two Mos heads are used because of the presence of an internal diode junction in the Mos between drain and source.

The limiter Li comprises a transistor T1. Diode D1 models the diode intrinsic to Mos transistor T1, whose anode is connected to the source of transistor T1 and whose cathode is connected to the drain of transistor T1. The l imitor Li comprises a transistor 12. The diode D2 models the diode intrinsic to the Mos transistor 12, whose anode is connected to the source of the transistor 12 and whose cathode is connected to the drain of the transistor 12. The gate of the transistors T1 and 12 is connected via a same resistor R to a terminal of a battery A. In practice, the voltage across the battery A polarizes the grill of the transistors T1 and 12 and thus keeps them on.

FIG. 5 shows a second example of a Li-imitator structure making it possible to keep two NMos-type transistors in the closed state, without the need for an external control circuit to polarize its gate.

Two accumulators A1 and A2 are connected in parallel in the same floor. The source of the transistor T1 is connected to a first terminal of the accumulator A1. The gate of the transistor T1 is connected to a second terminal of the accumulator A1 via a resistor R1. The source of the transistor 12 is connected to a first terminal of the accumulator A2. The gate of the transistor 12 is connected to a second terminal of the battery A2 via a resistor R2. Transistors T1 and 12 are connected by their source. The respective intrinsic diodes D1 and D2 of the MOS transistors T1 and 12 are also lustrous. The voltages at the terminals of the accumulators A1 and A2 polarize the respective gates of the transistors T1 and 12 and thus keep them on.

Even keeping the NMos transistors T1 and 12 permanently closed, their consumption remains relatively low in normal operation because the Mos gate oxide is a capacitor which therefore consumes no permanent current. As a result, a constant voltage is applied to their grill corresponding to the voltage of the accumulators A1 and A2, typically of the order of 3.3 V for LiFeP type accumulators.

As illustrated in FIG. 7, a battery 1 according to the invention advantageously comprises lithium-ion batteries LiFeP with a number of stages greater than or equal to 7 (in this case 8 in this example). Indeed, an accumulator of this type tolerates an overvoltage (voltage up to 4.2 V) and the overvoltage induced in the accumulators of a branch including a short-circuited accumulator does not induce their destruction or a security risk for such a large number of floors.

The first branch Br1 includes accumulators A1 1 to A18 connected in series. The second branch Br2 includes accumulators A21 to A28 connected in series. The third branch Br3 includes accumulators A31 to A38 connected in series. The fourth branch Br4 includes accumulators A41 to A48 connected in series. Limiters of currents Li 1 1 to Li 1 realize the parallel connection of the accumulators of the first and second branches. Current imitators Li 21 through Li 27 realize the parallel connection of the second and third accumulators. third branches. Imitators of currents L 31 to Li 37 realize the parallel connection of the accumulators of the third and fourth branches.

Simulations of malfunctions were carried out with a model of a battery 1 according to FIG. 7. For these simulations, the accumulators were assimilated to voltage sources of 3.3 V in series with an internal resistance of 0.01 Ω . The current imimeters were sized with a saturation current of 1 A, with a nominal resistance of 0.01 5Ω.

In the example of FIG. 7, the battery A26 suffers a malfunction in short circuit. FIG. 8 is a diagram showing the evolution of the intensity across the various branches following the appearance of the dysfunction. Due to the presence of current im Li 1 5, Li 25, Li 35 and Li 16, Li 26, Li 36, the transverse load currents from the accumulators A1 6, A 36 and A 46 remain relatively limited. As a result, the charging current received by the branch Br2 does not come from the transverse load currents but from the external connections of the branches Br1, Br3, Br4, which are not provided with limiters. The branches Br1, Br3 and Br4 therefore provide a current of load (broken line). Branch Br2 receives a load current (in dotted line), corresponding to the accumulation of load currents branches Br1, Br3 and Br4. Figure 9 is a diagram showing the voltage across the battery A26 (dotted) and the voltage across the accumulators Br2 branch (dashed) free of malfunctions. The voltage across the faulty accumulator A26 drops gradually to a value close to 0V. The voltage across the other accumulators of the branch Br2 increases gradually from a value of 3.3 V to about 3.8 V, to compensate for the voltage drop in the stage Et6. This voltage is largely bearable by the other batteries of the branch Br2 in LiFeP technology.

As illustrated in FIG. 10, the discharge rate of the accumulators A1 6, A36 and A46 (dashed line) is therefore considerably slower than the discharge rate of the accumulator A26 (in dotted lines). Gradually, the entire stage Et6 discharges and the voltage across the battery 1 drops accordingly. The discharge time of this faulty stage is of course dependent on the number of parallel connected accumulators and the saturation current of the current imitators.

In such a battery, it remains possible to balance the load of non-faulty floors even in the presence of a faulty stage. The circuit 2 can determine the presence of a faulty accumulator by identifying a branch absorbing a charging current from the other branches or by identifying a stage at the terminals of which the voltage varies abnormally with respect to the other stages, either during a load , or during a discharge. It is also possible to identify a stage containing a faulty accumulator from a significant variation in its discharge velocity or voltage level since it gradually discharges to 0V.

Figure 11 shows schematically an advantageous variant of battery connection in a stage. In this case, all the accumulators A1 to A5 of a stage And have a terminal connected to a common connection node NC via the respective current imitators Li 1 to Li 5. The other terminal of these accumulators A1 to A5 may be connected to another common connection node via other respective current imprinters.

Such a structure makes it possible on the one hand to use unidirectional current imitators. Such a structure makes it easy for anyone to determine which area of the battery is failing, while current imagers maintain electrical contact with the failing area. In addition, the balancing currents pass only through the load limiter associated with the relevant accumulator. There is thus no current limiter which sees charge or balance current flow to several accumulators, which limits losses and reduces their size. For this purpose, the circuit 2 is here connected to the common connection nodes. In addition, such a structure makes it possible to imitate the number of transistors integrated in the current imimeters.

For current imagers in the direction of the load (current from the common node to the accumulators), if an accumulator is short-circuited, the charging current supplied by the other accumulators of the stage will necessarily have to cross. its current imitator. The short-circuited battery will therefore be protected from excessive charging current.

For current imagers in the discharge direction (current from an accumulator to the common node), if an accumulator becomes short-circuited, the discharge currents supplied by the other accumulators of the stage will be limited by their respective current l imitors. The short-circuited accumulator will therefore be protected from excessive charging current by current imagers of other accumulators.

FIG. 12 schematically shows a unidirectional current imi L, based on a JFET transistor T3, mimicking the current in the sense of an accumulator to the common node NC.

Different criteria may be taken into account for sizing the saturation current and / or the saturation voltage of the current imitators.

In particular, it is possible to use current imagers whose saturation voltage is lower than the nominal voltage of each of the accumulators of the battery 1. It will also be possible to use a balancing circuit 2 configured to apply a balancing current to the accumulators remaining below the saturation currents of the current limiters.

The saturation current may also be defined at a rated current of an accumulator resulting in its complete discharge in one hour.

A battery 1 intended to power a motor vehicle electric motor typically has a nominal voltage of between 200 and 500 V. For such a battery, the current limiters can be sized to have a saturation intensity of between 200 mA and 2 A, for example of the order of 1 A. In order to limit the losses during charging or load balancing in the battery 1, the current limiters are advantageously sized to have a reduced resistance in the on state, typically less than or equal to 0.1 Ω, preferably less than 1 Ω, when the voltage at their terminals is lower than said saturation voltage.

Advantageously, the circuit 2 can perform voltage clipping at the terminals of the accumulators, for lithium-ion type accumulators unable to achieve this clipping naturally. Such clipping can be achieved by a circuit 2 of a relatively small volume and cost, because of the parallel connection of the accumulators of the same stage.

A storage device or power battery whose nominal voltage is generally greater than 100V will typically include several modules or batteries connected in series. Each module will then comprise several stages in series with several branches in parallel. In the case where an accumulator fails in one of the modules, the circuit 2 may advantageously control the short-circuiting of this module to ensure the continuity of service of the rest of the storage device.

Figure 13 illustrates an isolation circuit of a Mod module in case of failure thereof. Mod module comprises terminals B1 and B2 between which it applies its power supply potential difference. The isolation circuit comprises two power output poles P and N, intended to be connected to modules in series or to one of the power terminals of the power storage device. The power circuit comprises two branches connected in parallel between the poles P and N. A first branch includes the switch 11 in series with the module Mod. A second branch branch includes the switch.

The switch 12 is configured to be normally closed, the switch 11 being configured to be normally open. The switch 11 is configured to selectively open / close the branch including the module Mod. The switch 12 is configured to selectively open / close the branch branch. The closing of the switch 11 is controlled by the circuit 2. In the absence of control signal applied by the circuit 2, the switch 11 is kept open to automatically isolate the Mod module in case of malfunction. The closing of the switch 12 is controlled by default by the voltage between the terminals B 1 and B2. Thus, the normal presence of a voltage between the terminals B1 and B2 keeps the switch 12 open in the absence of other controls, which ensures the short-circuiting of the Mod module by default in the event of a malfunction. The opening of the switch 12 must be actively controlled by the circuit 2 in order to apply the voltage of the Mod module to the poles P and N.

The switches 11 and 12 may be MOSFET transistors, which can easily be appropriately sized at a relatively low cost. Transistors 11 and 12 may be of nMOS type.

FIG. 14 illustrates a system 4 comprising modules Mod1, Mod2, Mod3 connected in series. The module Mod 1 is connected between the poles P1 and P2, the module Mod2 is connected between the poles P2 and P3, the module Mod3 is connected between the poles P3 and P4. The isolation circuit of the module Mod 1 comprises switches 11 1 and 11 2, the isolation circuit of the module Mod2 comprises switches 121 and 11 2, the isolation circuit of the module Mod3 comprises switches 131 and I32. In the lustrous configuration, Mod 1, Mod 2, Mod 3 modules are operational. Consequently, the switches 11 1, 121 and 131 are closed and their switches 112, I22 and I32 are open, so that the modules Mod1, Mod2, Mod3 are connected in series.

Figure 14 it shines the system 4 when Mod2 module is malfunctioning. When the circuit 2 detects this malfunction, it opens the switch 121 and closes the switch I22. The Mod2 module is thus short-circuited. The Mod2 module can thus be isolated in order to avoid its load and thus avoid a more serious damage. The system 4 can therefore be used in a degraded manner while ensuring its continuity of service. The invention applies to a battery comprising at least two stages and at least three accumulators in each stage, although a larger number of stages and accumulators have been mentioned in the various embodiments described. Current limiters can be realized with bipolar transistors.

Below the saturation threshold, the current flowing through such a current limiter is then substantially defined by an affine function of the voltage.

Claims

Accumulator battery (1), characterized in that it comprises at least:

first and second stages (Et1, Et2) electrically connected in series, each stage including at least first to third accumulators (A1 1, A21, A31) electrically connected in parallel;

at least first and second current imitators (Li 1 1, Li 21) by means of which the first to third accumulators (A1 1, A 21, A 31) of said first stage (Et 1) are connected in parallel and through intermediate of which the first to third accumulators (A12, A22, A32) of said second stage (Et2) are connected in parallel, a current limiter being a component or circuit traversed by an increasing current with the voltage at its terminals when this voltage is below a saturation threshold, and traversed by a substantially constant saturation current when this voltage is greater than said saturation threshold.

An accumulator battery according to claim 1, further comprising a third current imprinter (Li3), said first to third accumulators (A1, A2, A3) of the first stage being connected to a common connection node (NC) by the intermediate respectively first to third current limiters (Li1, Li2, Li3).

An accumulator battery according to claim 2, wherein said first to third current imitators (Li 1, Li 2, Li 3) mimic the current unidirectionally between the common (NC) and the first to third accumulators (A1, A2, A3).

An accumulator battery according to any one of the preceding claims, wherein said current imagers each include a first JFET transistor whose gate is connected to the source, whose source is connected to a terminal of a accumulators of the first stage and whose drain is connected to a terminal of another of the accumulators of the first stage.

An accumulator battery according to any one of claims 1 to 3, wherein said current imagers each include a first depletion-type Mosfet transistor whose gate is connected to the source, whose source is connected to a source. terminal of one of the accumulators of the first stage and whose drain is connected to a terminal of one of the accumulators of the first stage.

The accumulator battery according to any of claims 1 to 3, wherein said current imagers each include a first transistor of an enrichment-type Mosfet and a control circuit configured to hold said Mosfet transistor closed.

The accumulator battery according to any one of claims 4 to 6, wherein said current limiters each include a second transistor of the same type as the first transistor and mounted head to tail with the first transistor.

8. Battery according to any one of the preceding claims, comprising at least five stages (Et1-Et8) electrically connected in series, each stage including at least first to third lithium-ion LiFeP type accumulators and electrically connected in parallel with each other. intermediate of at least two respective current limiters. 9. Battery according to any one of the preceding claims, wherein the nominal voltage across each of said accumulators is greater than the saturation voltage across the current limiters beyond which the current limiters are traversed by a current. saturation substantially constant.

The battery of claim 8, wherein each of said current limiters behaves as a resistive circuit having a resistance of less than 1 Ω when the voltage across it is less than said saturation voltage.

1 1. A battery as claimed in any one of the preceding claims, wherein said saturation current of each of the current limiters is at least 50% of the maximum current value for any voltage across said current limiter below the saturation threshold.

12. Battery according to any one of the preceding claims, wherein said saturation current of each of the current limiters is at least equal to the maximum current value for any voltage across said current limiter below the saturation threshold.

1 3. System comprising:

a battery according to claim 8 or 10;

a balancing circuit (2) connected to the terminals of each of the stages of the battery and configured to apply a balancing current to the accumulators of a stage, this balancing current having a maximum amplitude less than the said saturation current.

The system of claim 13, including a battery according to claim 9, and wherein the balancing circuit (2) is connected to a common connection node (NC) of the accumulators of a stage and configured to apply a balancing current to each of the accumulators of said stage, the balancing current of each of the accumulators having a maximum amplitude less than said saturation current divided by the number of accumulators of said stage.

15. System (3) comprising:

two batteries (Mod1, Mod2) according to any one of claims 1 to 12, said batteries being connected in series and each having first and second power output poles (P1, P2);

a security device associated with one of said batteries (Mod1) and comprising:

first and second switches (11 1, 11 2), the first switch being a normally open switch (11 1), the second switch being a normally closed switch (112), a supply voltage of said battery (Mod1) being applied as the default closing control signal of the second switch (112);

first and second branches connected in parallel between the first and second power output poles (P1, P2), the first branch including a battery and the normally open switch (11 1) connected in series, the second branch being selectively open / closed by the normally closed switch (112).

The system of claim 15, further comprising a control circuit (2) which, during use of the battery associated with the securing device, applies a control signal forcing the closure of the first switch and applies a control signal forcing the opening of the second switch.

7. System comprising:

a battery according to any one of the preceding claims;

a fault detection circuit connected to the terminals of each of the stages of the battery and configured to detect a malfunction of the battery when the voltage across one of said stages diverges voltages across the other stages.