FR3061369A1 - SECURING A LITHIUM BATTERY - Google Patents

Abstract

The method of managing a lithium battery (10) comprises the following steps: - providing a lithium battery (10) comprising a set (11) of accumulator modules (11i), a first pair (12a) of connections electric power supply for supplying a starter (21) and a second pair (12b) of electrical connections for supplying at least one electrical equipment (23); - measuring the voltage (Vi) across each of the accumulator modules (11i); comparing each of the measured voltages (Vi) with a first threshold value (Vsi); - providing a starter relay (13) connecting the first pair (12a) of electrical connections to the starter (21) so as to allow or prevent the passage of a first electric current (la) according to the comparison result;

Description

© Holder (s): COMMISSION OF ATOMIC ENERGY AND ALTERNATIVE ENERGIES Public establishment, LIMATECH Simplified joint-stock company.

fA) Agent (s): CABINET HECKE Société anonyme.

FR 3 061 369 - A1 (54) SECURITY OF A LITHIUM BATTERY.

(57) The method for managing a lithium battery (10) comprises the following steps:

- providing a lithium battery (10) comprising a set (11) of accumulator modules (11 i), a first pair (12a) of electrical connections intended to supply a starter (21) and a second pair (12b) of electrical connections intended to supply at least one electrical equipment (23);

- measure the voltage (Vi) at the terminals of each of the accumulator modules (11 i);

- compare each of the measured voltages (Vi), with a first threshold value (Vsi);

- providing a starter relay (13) connecting the first pair (12a) of electrical connections to the starter (21) so as to allow or prevent the passage of a first electric current (la) as a function of the comparison result;

Securing a lithium battery

Technical field of the invention

The invention relates to a method for managing the use and charging of a lithium battery, in particular that used for starting a combustion engine. The invention also relates to a device allowing such management.

State of the art

Lithium batteries are increasingly used to power all kinds of electronic devices. Most lithium batteries are for portable electronic devices. This type of battery is used in “cycling” mode and delivers an electric current having a relatively low intensity by discharging rather slowly, generally within a few hours.

Furthermore, lithium batteries take up a large amount of energy per unit of volume, and they can be dimensioned and configured to supply a current having a high intensity. These “power type” batteries are for example used in model making and are discharged in a few minutes or a few tens of minutes. However, their use in the field of transport by thermal engine vehicles, and more particularly in the field of the automobile and aeronautics, is less widespread.

Indeed, a lithium battery generally comprises several cells implementing highly sensitive electrochemical processes. Thus, unlike lead-acid batteries, the use and charge of this type of battery requires precise and continuous control of several parameters and for each of the battery cells. This is why current lithium batteries, especially those with a high energy density, have a management system or BMS (BMS for the acronym "Battery Management System"). In addition, the field of transport imposes particularly restrictive standards of reliability, security, and operation. Current BMS are not suitable for ensuring the safety of a single lithium battery intended to be associated with a portable device equipped with a heat engine, for example a road, sea or air vehicle or other devices with a heat engine .

Document WO 2012/74531 discloses a system with two batteries intended to power a heavy vehicle. The system comprises a first lithium battery dedicated exclusively to starting the engine of the vehicle, and a second lead battery dedicated exclusively to the various electronic devices of the vehicle. This document also discloses a BMS associated with the first battery. The BMS is only used to provide information, to a control system, on the state of charge or SOC (SOC for the acronym of "State of Charge"), the voltage at the terminals of the battery and the temperature of the drums. The latter prevents charging of the first battery by an alternator, especially when the temperature of the battery or its SOC is critical or even when there is a significant difference between the voltages across the terminals of the two batteries.

This system uses a main lead battery to meet the vehicle's electrical energy needs. It is an expensive and complicated battery system to control since it is necessary to monitor and manage two batteries at the same time.

Subject of the invention

An object of the invention consists in proposing a method for managing the use and the charge of a lithium battery, in particular that used by a vehicle with an internal combustion engine, making it possible to ensure effective safety of the vehicle and to lengthen the calendar life of said lithium battery.

We tend to achieve this objective by implementing a method for managing a lithium battery comprising the following steps:

a) provide a lithium battery comprising:

+ a set of accumulator modules, + a first pair of electrical connections intended to supply a starter of a heat engine of a vehicle, and configured to let a first current pass;

+ a second pair of electrical connections intended to supply at least one electrical equipment of said vehicle, and configured to let pass a second current having an intensity lower than the intensity of the first current;

b) providing a starter relay connecting the first pair of electrical connections to the starter so as to allow or prevent the passage of the first current;

c) measure the voltage across each of the accumulator modules in the assembly;

d) compare each of the measured voltages with a first threshold value;

e) preventing or interrupting the passage of the first current by means of the starter relay when at least one of the voltages measured for an accumulator module of the assembly is less than the first threshold value, the battery delivering the second current via the second pair of electrical connections.

The invention also provides a method for starting a heat engine by means of a lithium battery, implementing a method for managing the lithium battery according to the invention, in which the first pair of electrical connections is connected to a starter of the heat engine, and in which the second pair of electrical connections is connected so as to supply at least one electrical equipment. In addition, steps a) to e) are implemented before the engine is started. The heat engine can be associated with a vehicle, and the second pair of electrical connections can be connected to a dashboard having a plurality of electrical and electronic equipment of the vehicle.

In addition, a device for managing a lithium battery is provided, comprising a set of accumulator modules, the lithium battery being dimensioned to deliver a first electric current having an intensity greater than 50 A, via a first pair of connections. electrical, and to deliver a second electrical current having an intensity lower than the intensity of the first current divided by 2, via a second pair of electrical connections. The management system includes:

+ means for measuring the voltage across each of the accumulator modules in the assembly;

+ a switch system configured to keep the second pair of electrical connections connected to the lithium battery, and to connect / disconnect the first pair of electrical connections of the lithium battery as a function of the voltages measured at the terminals of each of the accumulator modules from the whole.

A lithium battery is also provided, comprising:

- a set of accumulator modules,

- a first pair of electrical connections configured to circulate a first electrical current having an intensity greater than 50 A;

- a second pair of electrical connections configured to circulate a second electrical current having an intensity less than the intensity of the first current divided by 2;

- the management system presented above.

Brief description of the drawings

Other advantages and characteristics will emerge more clearly from the description which follows of particular embodiments of the invention given by way of nonlimiting examples and represented in the appended drawings, in which:

- Figure 1 schematically illustrates a device for managing a lithium battery according to one embodiment.

- Figure 2 schematically illustrates an electronic device used for monitoring the voltages of a lithium battery according to one embodiment.

- Figure 3 schematically illustrates an electronic device used for balancing voltages and regulating voltages at the end of charging a lithium battery according to one embodiment.

detailed description

There is a tendency to improve the availability and safety of a vehicle with an internal combustion engine using a lithium battery for starting it and for supplying other equipment to the vehicle, by providing an innovative method and system for managing said battery.

The method and the management system advantageously make it possible, when certain critical conditions are observed, to cut off the supply of electrical energy to the starter while maintaining the supply of the other equipment. In addition, the management method and system are advantageously optimized to extend the calendar life of said lithium battery used in this type of device or vehicle.

The management method, according to an embodiment of the invention, includes a step of supplying said lithium battery (step a)). FIG. 1 represents a battery 10 comprising means for implementing the method according to one form of the invention. The battery 10 is in particular associated with a management device 1 (BMS).

As illustrated in FIG. 1, the lithium battery 10 comprises a set 11 of accumulator modules 11 i. The assembly 11 comprises n accumulator modules 11i having an index i of between 1 and n, where n is an integer greater than 1.

The accumulators 11 i of the battery 10 can be connected in series or in parallel. Furthermore, a first subset of accumulators of the assembly 11 can be connected in series, and a second subset of accumulators of the assembly 11 can be connected in parallel.

Preferably, the accumulators 11 i of the battery 10 are identical. According to the embodiment of Figure 1, the battery 10 comprises four accumulator modules 11 i.

The battery 10 also includes a set of electrical connections at the output of the battery intended to deliver the electrical energy stored in the battery 10 to several components. In particular, the battery 10 comprises a first pair 12a of electrical connections intended to supply a starter 21 of a heat engine 22 of a vehicle 20.

The term “heat engine” means any machine for converting chemical energy, in the form of fuel and oxidizer, into mechanical energy.

This includes in particular reciprocating or rotary piston engines, for example 2-stroke or 4-stroke, turbines, turbomachines, internal or external combustion machines.

The first pair 12a is configured to allow a first current Ia to pass. This current la is delivered by the battery 10 and it is intended for the starter

21. Preferably, the first pair of connections 12a is dedicated exclusively to supplying the starter 21 with electrical energy.

In addition, the battery 10 comprises a second pair 12b of electrical connections intended to supply, at least one electronic equipment 23 of the vehicle 20. The equipment 23 is different from the starter 21 of the heat engine 22, in other words, the equipment 23 n is not a device intended for starting the heat engine 22. The second pair 12b of electrical connections is configured to let a second current Ib having an intensity less than the intensity of the first current la.

Furthermore, the second pair 12b can also be configured so as to supply the starter 21, on an ad hoc basis. Thus, the starter 21 is supplied, in this case, both by the first pair 12a and the second pair 12b of electrical connections. Preferably, the second pair of connections 12b is dedicated exclusively to supplying electrical energy to one or more pieces of equipment 23 of the vehicle, other than the starter 21.

Preferably, the second pair 12b is configured so as not to be able to supply the starter 21 alone.

In addition, the first pair 12a and the second pair 12b of electrical connections may include cables made of an electrically conductive material for circulating an electric current. Preferably, the dimensions of the cables, in particular the diameters of the cables of the first pair of connections 12a are greater than the dimensions, in particular the diameters of the cables of the second pair 12b.

Advantageously, the method implements a starter relay 13. In other words, the method comprises a step of supplying the starter relay 13 connecting the first pair 12a of electrical connections to the starter 21 (step b)). The starter relay 13 enables or prevents the passage of the first current Ia, delivered by the battery 10, of the first pair 12a of electrical connections in the direction of the starter 21.

The starter relay 13 is controlled by the management device 1 of the battery 10, which will be described in more detail below. The starter relay 13 is mainly intended to cut the passage of the first current la to the starter 21 under certain conditions.

Indeed, the method further comprises a step of measuring the voltage Vi, at the terminals of each of the accumulator modules 11 i of the assembly 11 (step c)).

As illustrated in FIG. 1, the management device 1 comprises a measuring device 2. The latter is configured to measure the voltage across each of the accumulator modules 11 i.

The measuring device 2 is also configured to measure several parameters of the battery 10 and its modules 11i. Preferably, the measurement device 2 is configured to measure the temperature Tb of the battery 10, and the state of charge Ci of each of the accumulator modules 11 i of the assembly 11.

The measuring device 2 can then comprise means for measuring the voltage 2a, means for determining the state of charge 2b, and means for measuring the temperature 2c.

Furthermore, the management device 1 also includes a calculation unit 3 configured to retrieve the measurements made by the measurement device 2, and to process and analyze these measurements.

The measurement, processing and analysis of the various quantities associated with the battery 10 and its accumulator modules 11 i can be sequential or continuous.

Furthermore, the measurement means 2a can be configured to simply take, for comparison, the voltage across the terminals of an accumulator module 11 i. For example, the method can use electrical connections so that the accumulator module 11 i is mounted in parallel with an electrical or electronic device configured to analyze the voltage across the terminals of the module 11i without quantifying it. According to a preferred embodiment of the invention, the measuring device 2 and the calculation unit 3 are formed by a single electronic circuit 80 partially illustrated in Figures 2 and 3, and described in more detail below.

The method further comprises a step of comparing each of the measured voltages Vi, with a first threshold value Vsi (step d)). More precisely, the calculation unit 3 compares each of the voltages measured Vi at the terminals of each of the accumulator modules 11 i of the assembly 11 with a first threshold value Vsi.

The first threshold value Vsi can correspond to a critical voltage value of the accumulator modules 11i, below which the accumulator modules risk being in a critical discharge state. Under these conditions, the accumulator modules 11 i risk being irreversibly damaged, in particular if they are stressed by electrical devices requiring a high voltage or current intensity to operate, such as a starter of a thermal motor.

Indeed, a deep discharge of an accumulator module of a lithium battery (i.e. a voltage across the module below a certain threshold), can lead to irreversible deterioration of the accumulator module. This deterioration can be potentially dangerous due to abnormal production of hydrogen in the accumulator module causing it to swell.

Advantageously, the first threshold value Vsi is a value common to the various accumulator modules 11i of the assembly 11. This embodiment makes it possible to facilitate the calculation and the processing of the various measured voltage values Vi, in particular when the modules accumulator 11 i of the assembly 11 are identical.

The accumulator modules 11i can be different. Therefore, the characteristics and specifics of the battery modules may be different. Thus, the first threshold value Vsi can be specific for each of the accumulator modules 11 i of the set 11.

As a result, each of the accumulator modules 11i of the assembly 11 has a first threshold value Vs, which is representative of it. In other words, the first threshold value Vsi can be a single-column matrix (Vs,), with 1 <i <n where n corresponds, to the number of accumulator modules 11i of the set 11. According to this embodiment, each coefficient Vs, of index i, corresponds to a first threshold value Vs, associated with the accumulator module 11i of index i.

Furthermore, the measured voltages Vi also constitute a single-column matrix (V,) with 1 <i <n. Each coefficient V, of index i, corresponds to the voltage measured across the terminals of the accumulator module 11 i of index i. Thus, the process comparison step consists in comparing the single-column matrix (V,) with the single-column matrix (Vs,). In other words, the coefficient V, of index i of the matrix (V,) is compared to the coefficient Vs, of index i of the matrix (Vs,), with 1 <i <n.

After the step of comparing each of the voltages Vi with the first threshold value Vsi, the management device 1 activates the starter relay 13 so as to prevent the passage of the first current la from the first pair 12a of connections towards the starter 21 , when at least one of the measured voltages Vi is less than the first threshold value Vsi.

Furthermore, for the embodiment in which the first threshold value Vsi is a single-column matrix (Vs,), the starter relay 13 is activated when at least one coefficient V, of index i of the matrix (V) is less than the coefficient Vs, of index i of the matrix (Vs,), with 1 <i <n.

However, the battery 10 and the management device 1 do not prevent the supply of electrical energy to the other electronic equipment 23, for example an on-board computer, security devices, etc. (step

e)). Indeed, although a measured voltage Vi is less than the first threshold value Vsi, the battery 10 delivers the second current lb via the second pair 12b of electrical connections (when the general state of charge of the battery 10 allows it) .

Indeed, during the interruption of the current la, the management device 1 will note an increase in the voltage Vi across the terminals of the modules 11 i, advantageously above the first threshold value Vsi. Furthermore, if the second current lb is maintained for a certain period while the device ensuring the recharging of the battery (for example an alternator) is not operational, then the voltage Vi across the terminals of the modules 11i will necessarily decrease. Under these conditions, the voltage Vi across the terminals of the modules 11i will drop below the first threshold value Vsi. In order to envisage this scenario, the management method also provides for alerting the driver or the user of the vehicle and / or interrupting the current lb to protect the battery from a deep discharge, if the current la of the starter is zero and if the voltage Vi is less than the first threshold value Vsi.

Preferably, steps c) to e) are consecutive.

A lithium battery offers very specific specific energy (energy / mass) and energy density (energy / volume), particularly in comparison with lead batteries or Ni-Cd batteries which are usually used in the field of transport by vehicle with thermal engine. A lithium battery is light and has a longer lifespan. Furthermore, the weight of the equipment is considered to be an important characteristic in the field of vehicles, in particular in the field of aeronautics. Thus, the management method according to the invention makes it possible to take advantage of the advantages of the use of a lithium battery in a vehicle with an internal combustion engine, while ensuring the operational safety of the lithium battery, and therefore of the vehicle.

Preventing the engine from starting while allowing the lithium battery to power the other equipment in the vehicle makes it possible to use only one battery and dispense with the use of a battery dedicated to starter and another battery dedicated to other equipment. This characteristic also ensures the safety of the battery by preventing its irreversible damage. In addition, it improves vehicle safety, preventing vehicle mobility, while there would be uncertainty about the level of battery safety (hydrogen production and swelling) and the ability to restart. the internal combustion engine after a stop, or an uncertainty about the power capacity of other equipment during the mobility of the vehicle. In particular, safety equipment and navigation equipment.

The invention also provides a device 1 for managing the lithium battery 10 comprising the set 11 of accumulator modules 11i. The lithium battery 10 is dimensioned so as to deliver the first electric current Ia having an intensity greater than 30A and preferably greater than 50A, via a first pair 12a of electrical connections. In addition, the battery 10 is dimensioned to deliver a second electric current lb having an intensity lower than the intensity of the first current divided by 2 (lb <la / 2). The second current 1b is delivered by the second pair 12b of electrical connections.

The management device 1 also comprises the means 2a for measuring the voltage Vi at the terminals of each of the accumulator modules 11i of the assembly 11. Preferably, the measuring means 2a are included in the measuring device 2.

Furthermore, the measurement means 2a may comprise one or more conventional systems, such as a digital voltmeter, for measuring the voltage across the terminals of an accumulator module 11 i. Preferably, the measurement means 2a comprise one or more voltage measurement sensors. The choice of the measurement system or systems is determined by a person skilled in the art as a function of the elements included in the battery 10 and in the management device 1, and the measurement accuracy envisaged.

Advantageously, the management device 1 comprises a switch system 70 configured to keep the second pair 12b of electrical connections connected to the lithium battery 10. The switch system 70 is also configured to connect / disconnect the first pair 12a of electrical connections of the lithium battery 10 as a function of the voltages measured Vi at the terminals of each of the accumulator modules 11 i of the assembly 11.

Preferably, the management device 1 comprises a calculation unit 3 configured to analyze the voltage measurements of the modules, and possibly control the switch system 70 as a function of the analysis of the voltages measured Vi at the terminals of the accumulator modules 11 i.

Advantageously, the measurement means 2a can be configured to take the voltage across the terminals of an accumulator module 11 i. For example, the management device may include electrical connections so that the accumulator module 11i is mounted in parallel with an electronic or electrical device 80i, configured to directly analyze the voltage across the terminals of the module 11i without being obliged to quantify. For example, the device 80i can include one or more voltage comparators.

According to an embodiment illustrated in Figures 2 and 3, the electronic device 80i is mounted in parallel with an accumulator module 11 i. The device may include voltage dividing bridges made by resistors R1, R2, R3 and R4. In addition, the device 80i includes voltage comparators U1 and U2 and a voltage reference Vref. It is also possible to use low-consumption voltage comparators with integrated voltage reference.

The comparator U1 is mounted in the device 80i so that it receives at least one input voltage which depends directly on the voltage Vi across the terminals of the accumulator module 11i. Said input voltage is compared with a predetermined voltage Vref, or an internal reference voltage of the comparator U1.

In fact, said input voltage representative of the voltage Vi is compared with a predetermined voltage which is defined from a reference voltage Vref. In a particular embodiment, the predetermined voltage comes from an input of the comparator U1.

In addition, the output of comparator U1 can be connected to a first logic function "or" (not shown in the figures), itself connected to an active device, for example an indicator light and / or the starter relay.

13. Therefore, depending on the output signal of comparator U1, the logic function "or" will be activated.

The device 80i can be mounted in parallel with each of the accumulator modules 11i. The stages formed by devices 80i can then be connected to a logic function "or" and form an electronic global analysis device 80.

Preferably, the switch system 70 can have at least a first state E1 _Πand a second state E1 _o .

According to an exemplary embodiment, the switch system 70 is configured so as to be in the first state E1 _cc so that the first pair 12a of electrical connections is able to allow the first current to flow. In other words, the switch system 70 is in the first state E1œ so that the battery 10 can supply a load in series (eg the starter 21) via the first connection pair 12a.

The switch system 70 is also configured so as to be in the second state E1 _O so as to disconnect the first pair of connections 12a from the battery 10. In other words, the battery 10 does not deliver the first current la to a load via the first pair of connections 12a.

Furthermore, the switch system 70 may include an electronic switch, for example a transistor, or a mechanical switch for example an electromechanical microsystem (MEMS). Those skilled in the art can also use other switch systems depending on the devices included in the battery 10 and the management device 1.

The invention further provides a lithium battery 10 comprising the elements described above. The lithium battery includes in particular:

- A set 11 of accumulator modules 11 i;

- A first pair 12a of electrical connections configured to circulate a first electrical current Ia having an intensity greater than 30 A, and preferably greater than 50 A;

- A second pair 12b of electrical connections configured to circulate a second electrical current Ib having an intensity less than the intensity of the first current divided by 2 (Ib <la / 2); and

- The management device 1 described above.

The management device and the lithium battery described above make it possible to take advantage of the advantages of using a lithium battery in a vehicle with an internal combustion engine, while guaranteeing the operating safety of the lithium battery, and because of the vehicle.

According to one embodiment, the method for managing the lithium battery 10 authorizes the passage of the second current Ib via the second pair 12b of electrical connections, even before the step of measuring the voltage Vi, at the terminals of each of the modules of accumulator 11 i of the assembly 11.

Thus, the method advantageously makes it possible to supply, by the lithium battery, important equipment of the vehicle before the engine even starts and therefore before the vehicle moves. Advantageously, the driver of the vehicle can have information on the operating state of the equipment of the vehicle, in particular the state of charge of the battery and the safety equipment of the vehicle even before the starting of the vehicle, in particular the starting of the thermal motor.

According to one embodiment, the method can also include a step of comparing each of the measured voltages Vi with a second threshold value Vs'i.

In the same way as for the first threshold value Vsi, the second threshold value Vs'i can be a value common to the different accumulator modules 11 i of the assembly 11.

The second threshold value Vs'i can be specific for each of the accumulator modules 11i of the set 11. Therefore, each of the accumulator modules 11 i of the set 11 has a second threshold value Vs'i which is representative for him. The second threshold value Vs'i can be a single-column matrix (Vs'O, with 1 <i <n where n corresponds to the number of accumulator modules 11i of the set 11. Each coefficient Vs'i of index i, corresponds to a second threshold value Vs'i associated with the accumulator module 11i of index i.

In this case, the process comparison step consists in comparing the uni-column matrix (V,) with the uni-column matrices (Vs,) and (Vs',). In other words, the coefficient V, of index i of the matrix (V,) is compared to the coefficients Vs, and Vs', of index i of the matrices (Vs,) and (Vs'O, with 1 <i <n .

After this comparison step, the management method advantageously provides for a step of transmitting information W when at least one of the voltages measured Vi for an accumulator module 11 i of the set 11 is greater than the second threshold value Vs'i. Preferably, the information W is visual, sound or digital information.

Preferably, the information W is also transmitted when at least one of the voltages measured Vi for an accumulator module 11i of the assembly 11 is less than the first threshold value Vsi.

According to the embodiment illustrated in FIG. 2, the comparator U2 is mounted in the device 80i so that it receives at least one input voltage which depends directly on the voltage Vi present at the terminals of the accumulator module 11 i .

Said input voltage representative of the voltage Vi is compared with a predetermined voltage which is defined from the reference voltage Vref. In a particular embodiment, the predetermined voltage comes from an input of the comparator U2.

The output of the comparator U2 can be connected to a second logic function "or" configured to transmit the information W, for example to an alert device such as an indicator light, as a function of the output signal of the comparator U2.

Preferably, the first logic function "or" and the second logic function "or" can consist of a single logic function whose inputs are connected at least to the outputs of the comparators U1 and U2. Said logic function can have a single output connected, for example, to a warning light to transmit information W.

Said logic function can also include at least two outputs in order to transmit two distinctive alerts associated respectively with the output signals of the first U1 and second U2 comparators.

Furthermore, when the first threshold value Vsi or the second threshold value Vs'i are single-column matrices (Vs,) and (Vs'i), the information W is preferably transmitted when at least one coefficient V, of index i of the matrix (V,) is less than the coefficient Vs, having the index i of the matrix (VS,), or greater than the coefficient Vs'i having the index i of the matrix (Vs'i) .

The second threshold value Vs'i can be representative of an overload state of the accumulator module 11i. This situation can occur in the event of failure of a device for regulating the charge of the lithium battery 10.

Overloading a lithium accumulator module can cause deterioration of the module, thermal runaway and inflammation of the module, and therefore of the lithium battery. The risk of thermal runaway of a lithium accumulator module constitutes a major obstacle to the use of this type of accumulator which complies with safety and reliability standards in the field of vehicles with thermal engine, in particular the field of aircraft. where safety is a major concern for manufacturers and airlines.

Consequently, the transmission of information W advantageously makes it possible to alert the user or the driver of the vehicle of the critical state of the lithium battery, allowing him to take the measures necessary to stabilize and make the lithium battery more reliable. , for example by disconnecting it, cooling it, discharging it or recharging it.

Thus, the method makes it possible to improve the safety of the vehicle, in particular by providing an additional safety measure in the event of failure, for example, of a device for regulating the charge of the lithium battery 10.

Advantageously, the method can provide for the disconnection of the accumulator module 11 i having a measured voltage Vi greater than the second threshold value Vs'i of the battery 10. This embodiment advantageously makes it possible to continue charging the modules 11i having voltages "Normal" (lower than the second threshold values Vs'i) while securing the "critical" module having a voltage Vi greater than the second threshold value Vs'i.

Furthermore, the management method may include a step consisting in connecting the accumulator module 11i, having a measured voltage Vi greater than the second threshold value Vs'i, to an electrical load 30i consuming electrical energy. In fact, the management device 1 may include a switching system configured to connect the electric charge 30i to the accumulator module 11i having a voltage Vi at its terminals greater than the second threshold value Vs'i. The management method thus makes it possible, and advantageously, to discharge said accumulator module in order to avoid the appearance of the phenomenon of thermal runaway.

Furthermore, the management method can provide, after the discharge step via the electrical charge 30i, a step of disconnecting the accumulator module from the charge 30i. In other words, the accumulator module i which has been connected to the electric charge 30i, is disconnected from this charge when the voltage measured Vi across the terminals of said accumulator module 11i becomes lower than the second threshold value Vs'i. This avoids unnecessary discharge of the accumulator module 11i when the risk of thermal runaway has diminished.

According to the embodiment illustrated in FIG. 3, the comparator U3 is mounted in the device 80i so that it has at least one input voltage which depends directly on the voltage Vi across the terminals of the accumulator module 11i. Said input voltage is representative of the voltage Vi. The comparator U3 can be connected to a transistor Q4 itself connected to a balancing resistor Req which constitutes the load 30i. Depending on the output signal from comparator U3 to transistor Q4, the accumulator module will be connected directly to the balancing resistor Req. Furthermore, the resistor R23 is a hysteresis resistor ensuring a frank tilting of the output signal of the comparator U3.

The method also provides additional measures to the measures described above to improve the safety of the battery and of the vehicle, and to extend the calendar life of the lithium battery. In fact, most vehicles with an internal combustion engine include means for recharging the vehicle battery, in particular an alternator.

The battery management method can advantageously provide steps dedicated to balancing the lithium battery 10 at the end of charging by monitoring the state of charge of each of the accumulator modules 11i of the assembly 11.

More particularly, the method may include a step of determining the state of charge Ci of each of the accumulator modules 11 i of the assembly 11. The determination of the state of charge can be carried out by the measuring device 2 comprising the means 2b. Preferably, the state of charge is determined by measuring the no-load voltage Vo, at the terminals of each of the accumulator modules 11 i of the assembly 11. Thus, the means 2c and the means for measuring the voltage 2a can be the same, which reduces the number of steps in the management process. The open-circuit voltage measurements are then processed by the calculation unit 3 to determine the state of charge Ci of each of the accumulator modules 11 i of the set 11.

According to an exemplary embodiment, all 11 of accumulator modules 11i are charged, in particular by an alternator of the vehicle with an internal combustion engine 20.

The modules 11i can also be loaded when the vehicle is stationary and the heat engine is not started. For example, the battery can be charged by a charging device which is not included in the vehicle 20. Said charging device can be supplied with electrical energy by an electricity distribution network.

The battery 10 is charged by means of an electric current so as to reach an end of charge state Cfi for each of the accumulator modules 11i of the set 11. The end of charge state for a module i can be detected when, for example, the no-load voltage Vo, is between an end-of-charge voltage Vf and a maximum admissible voltage Vmax, predetermined for each of the modules 11 i of index i.

Generally, the state of charge of a lithium battery module and its no-load voltage are directly dependent. The manufacturers or the users can constitute an abacus to have a correspondence between these two quantities, during the charging and discharging of the accumulator module. In addition, for a state of charge of between 20% and 80% of optimal operation, the state of charge of the module varies almost linearly as a function of the no-load voltage.

The method advantageously comprises a step intended for individually discharging the accumulator modules 11 i having reached the end of charge state Cfi by means of an additional electrical charge 31. The discharging of said modules is carried out so that the state of load Ci of each of these modules reaches a state of charge included in the state of charge range [80%, 95%], and preferably between [90%, 95%]. Furthermore, the end of charge state of the modules 11 i is greater than 96% and preferably greater than 99%.

According to a particular embodiment, the management method also makes it possible to partially discharge the elements by calling up a control of the duration during which the discharge resistance (the charge 30i) is connected to the accumulator module 11i. According to another particular embodiment, the charging of an accumulator module 11i can be interrupted as soon as its state of charge Ci reaches 80%, and preferably 90%.

According to an exemplary embodiment, the modules 11i are LiFePo4 modules of the ANR26650 type sold by the company A123 Systems. For this type of accumulator module, it is recommended to finalize the charge by means of a floating voltage equal to 3.6V (Vf, = 3.6 V).

The management method according to the invention makes it possible to balance the end of charge of the modules so that the empty voltage across the terminals of the modules is adjusted substantially to 3.4 V (Vo, = 3.4 V). Thus, the lithium battery 10 is advantageously preserved or stored so as to have a state of charge substantially equal to 95%.

It has been observed that this small deficit in capacity of the lithium battery, generated by the balancing step of the management method, makes it possible to have a considerable gain over the calendar life of the lithium battery.

Indeed, tests have been implemented for lithium batteries for electric cars. These tests compared two modes of charging / discharging this type of battery over several months of use.

These accelerated aging tests were carried out at 45 ° C.

The first mode consisted in storing a first battery daily with a state of charge of 100% (fully charged), between 8 p.m. and 8 a.m. The battery was used the rest of the day. The state of charge of the battery is maintained, depending on this mode of use, between 60% and 100% during all the daily cycles of use.

The second mode consisted in storing daily a second battery of the same type with a state of charge of 60%, between 20h and 08h. The battery was used the rest of the day. The state of charge of the battery was maintained, according to this mode of use, between 60% and 20% during all the daily cycles of use.

These tests showed that the estimated lifespan of the second battery was thirty months, while the first battery had reached the estimated end of life after 12 months. Thus, a gain in calendar life of the battery can reach a factor of 2.5 by using balancing according to the management method.

In fact, contrary to the recommendations of the manufacturers of lithium accumulator modules, encouraging users to maintain a state of charge substantially equal to 100% and by maintaining a floating voltage equal to 3.6 V for LiFePo4 and 4 batteries , 2 V for Lithium polymer batteries, the balancing process unexpectedly increases the lifespan of the lithium battery by 100% and more, by lowering the state of charge at the end of the battery charge a few percent.

To ensure optimum safety of the lithium battery and of the vehicle, the management method also provides for monitoring the temperature of the lithium battery. The management method can then include a step for measuring the temperature Tb of the battery 10. The measurement is carried out by the measurement device comprising the temperature measurement means 2c.

The measurement means 2c are configured to provide information on the temperature of the battery 10. They can comprise several temperature sensors distributed in the battery 10, for example distributed over the surface of the battery 10. The temperature sensors can comprise a thermometer, thermocouple, thermistor, or any system to provide a temperature measurement.

Then, the temperature of the battery Tb is compared by the calculation unit 3 to a minimum temperature threshold value Tmin and / or to a maximum temperature threshold value Tmax greater than the minimum temperature threshold value Tmin.

Preferably, the minimum temperature Tmin and maximum temperature Tmax thresholds are respectively -30 ° C and +55 ° C, and even more preferably, are 0 ° C and +50 ° C respectively.

After this comparison step, the management device transmits a signal W ′ which can be visual, audible or even digital, in particular to the user or to the driver of the vehicle, when the measured temperature of the battery Tb is below the threshold value of minimum temperature Tmin or higher than the maximum temperature threshold value Tmax.

Advantageously, the method makes it possible to alert the user of a critical state, from a thermal point of view, of the lithium battery. Indeed, lithium batteries are very sensitive to temperature.

The use of a high temperature lithium battery (Tb greater than Tmax) increases the risk of thermal runaway of an accumulator module 11i of battery 10. Thermal runaway is generally observed for temperatures d '' a lithium battery around 90 ° C approximately.

In addition, at low temperatures, the mobility of the carriers decreases and the internal impedance increases within a lithium battery. Thus, the ability to draw a high current from the battery 10 is limited, which makes it more difficult to supply a high current to start a heat engine. A possible attempt to start the heat engine under these temperature conditions risks damaging the lithium battery 10. In general, it is strongly recommended that you recharge or intensively stress a lithium battery at low temperatures. Charging or intense use of the battery under these conditions can damage it irreversibly, for example by producing metallic lithium which can cause internal short circuits. Here, by low temperatures is meant temperatures below - 10 ° C, and preferably below 0 ° C.

Thus, the battery 10 is advantageously provided with an electric heating device 50 controlled by the management device 1. In fact, the management method provides for the activation of the heating device 50, preferably, by the management device 1, when the measured temperature Tb of the battery is lower than the minimum temperature threshold value Tmin. In addition, the heating device 50 is supplied with electrical energy by the lithium battery 10. The heating device can comprise heating resistance sheets configured so as to be mounted on the battery 10.

Furthermore, the activation of the heating device 50 can be carried out by the user or the driver of the vehicle when he has received the visual, sound or digital signal W '.

The method advantageously uses the energy of the battery 10 to heat the lithium battery 10 to a temperature above the temperature threshold Tmin so that the battery 10 is capable of delivering the first electric current sufficient for starting the heat engine 21 of the vehicle, while safe. In addition, the amount of electrical energy consumed by the heater 50 to raise the temperature of the battery Tb to an optimal temperature is relatively small. By optimal temperature is meant a temperature at least between the minimum temperature Tmin and maximum temperature Tmax thresholds, and preferably substantially equal to 20 ° C.

For example, for the LiFePo4 modules described above, the electrical charge taken is 0.21% per degree Celsius rise in battery temperature 10. Thus, only 10% of the energy stored in the battery 10 is sufficient to raise the temperature of the battery Tb from -25 ° C to 20 ° C for a battery having a capacity of 15 Ah. Furthermore, after allowing the heat engine to start, the battery 10 is preferably charged via an alternator to recover the energy expended during the heating step.

The electric heating device 50 is preferably disconnected from the lithium battery 10 when the temperature of the battery Tb reaches the minimum temperature threshold value Tmin. Even more preferably, the user or the driver of the vehicle can leave the electric heating device 50 activated until the temperature of the battery Tb stabilizes at a temperature which may be between 10 ° C. and 20 ° C.

According to an exemplary embodiment, the functionalities described above of the device 80 of FIG. 1 can be installed on an electronic card advantageously having a reduced size of the order of 50 x 60 mm. The static consumption of the device 80 is very reduced and it is of the order of 140 μΑ. Therefore, the device 80 can manage a lithium battery for 4 years or more of storage without special supervision.

In addition, there is a tendency to further improve the safety of the vehicle 20 with an internal combustion engine using the lithium battery 10, by also providing a method for starting the internal combustion engine.

According to one embodiment, a method is provided for starting a heat engine 22 by means of a lithium battery 10, implementing a method for managing the battery according to any embodiment described above. .

According to this embodiment of the starting method, the first pair 12a of electrical connections is connected to a starter 21 of the heat engine 22 of the vehicle 20. In addition, the second pair 12b of electrical connections is connected so as to supply at least one electrical or electronic equipment 23.

Preferably, the heat engine 22 is associated with a vehicle 20, and the second pair 12b of electrical connections is connected to a dashboard having a plurality of electrical and electronic equipment 23 ′ of the vehicle 20.

Advantageously, the method provides that steps a) to e) are implemented before the engine 22 is started. The method prevents the engine starting operation which requires a large current. This advantageously makes it possible to avoid degradation or even destruction of the battery 10 when at least one of the modules 11i of the battery 10 is not able to function normally, in particular when due to its state of charge, its state of health or its temperature, it is not able to participate in the supply of an important current.

The method also makes it possible to prohibit the starting of the vehicle so as not to deactivate the battery 10 while the vehicle is mobile, and therefore to put out of service vital equipment for the proper functioning of the vehicle. Thus, the safety of the users of the vehicle is improved.

Claims (12)

Claims 1. Method for managing a lithium battery (10) comprising the following steps: a) supply a lithium battery (10) comprising: + a set (11) of accumulator modules (11 i), + a first pair (12a) of electrical connections intended to supply a starter (21) of a heat engine (22) of a vehicle (20), and configured to pass a first current (la); + a second pair (12b) of electrical connections intended to supply at least one electrical equipment (23) of said vehicle (20), and configured to let pass a second current (lb) having an intensity lower than the intensity of the first current ( the) ; b) providing a starter relay (13) connecting the first pair (12a) of electrical connections to the starter (21) so as to allow or prevent the passage of the first current (la); c) measuring the voltage (Vi) at the terminals of each of the accumulator modules (11 i) of the assembly (11); d) comparing each of the measured voltages (Vi), with a first threshold value (Vsi); e) preventing the passage of the first current (la) by means of the starter relay (13) when at least one of the measured voltages (Vi) for an accumulator module (11 i) of the assembly (11) is less than the first threshold value (Vsi), the lithium battery (10) delivering the second current (lb) via the second pair (12b) of electrical connections. 2. Management method according to claim 1, characterized in that it comprises, before step b) of measurement, the following step: b ') authorize the passage of the second current (lb) via the second pair (12b) of electrical connections. 3. Method according to one of claims 1 and 2, characterized in that it comprises the following steps: c ¹ ) compare each of the measured voltages (Vi), with a second threshold value (Vs'i); d ¹ ) transmit visual, sound or digital information (W) when at least one of the measured voltages (Vi) for an accumulator module (11 i) of the assembly (11) is greater than the second threshold value ( Vs'i). 4. Method according to claim 3, characterized in that it comprises the following successive steps: e ¹ ) connecting the accumulator module (11i) having a measured voltage (Vi) greater than the second threshold value (Vs'i), to an electrical load (30i) consuming electrical energy; P) disconnecting said accumulator module (11 i) from the electric charge (30i) when the measured voltage (Vi) at the terminals of said accumulator module (11 i) becomes lower than the second threshold value (Vs'i). ⁵ 5. Method according to any one of the preceding claims, characterized in that it comprises the following steps: + determine the state of charge (Ci) of each of the accumulator modules (11 i) of the assembly (11); + charge the set (11) of accumulator modules (11i) by means of an electric current so as to reach an end of charge state (Cfi) so that each of the accumulator modules (11 i) of the 'set (11); + individually discharge the accumulator modules (11i) having reached the end of charge state (Cfi) by means of an additional electrical charge (31) so as to reach a charge state included in the state interval of charge [90%, 95%], the end of charge state (Cfi) being greater than 96%. 6. Method according to any one of the preceding claims, characterized in that it comprises the following steps: + measure the temperature (Tb) of the lithium battery (10); + compare the measured temperature (Tb) to a minimum temperature threshold value (Tmin) and / or to a maximum temperature threshold value (Tmax) greater than the minimum temperature threshold value (Tmin); + transmit a signal (W ') when the measured temperature (Tb) is less than the minimum temperature threshold value (Tmin) or greater than the maximum temperature threshold value (Tmax). 7. Method according to claim 6, characterized in that it comprises the following steps: + supply the lithium battery (10) further comprising an electric heating device (50); + activate the heating device (50) so as to heat the lithium battery (10) when the measured temperature (Tb) is lower than the minimum temperature threshold value (Tmin), the heating device (50) being powered by the lithium battery (10). 8. Method according to claim 7, characterized in that the electric heating device (50) is disconnected from the lithium battery (10) when the temperature of the battery (Tb) reaches the minimum temperature threshold value (Tmin). 9. A method of starting a heat engine (22) by means of a lithium battery (10), implementing a method of managing the lithium battery (10) according to any one of claims 1 to 8 , in which the first pair (12a) of electrical connections is connected to a starter (21) of the heat engine (22), and in which the second pair (12b) of electrical connections is connected so as to supply at least one electrical equipment (23), characterized in that steps a) to e) are implemented before starting the heat engine (22). 10. Starting method according to claim 9, characterized in that the heat engine (22) is associated with a vehicle (20), and in that the second pair (12b) of electrical connections is connected to a dashboard having a plurality of electrical and electronic equipment (21) of the vehicle (20). 11. Management device (1) of a lithium battery (10) comprising a set (11) of accumulator modules (11 i), the lithium battery (10) being dimensioned to deliver a first electric current (/ a) having an intensity greater than 50 A, via a first pair (12a) of electrical connections, and for delivering a second electrical current (Ib) having an intensity less than the intensity of the first current (Ja) divided by 2, via a second pair (12b) of electrical connections, characterized in that it comprises: + means for measuring the voltage (Vi) at the terminals of each of the accumulator modules (11 i) of the assembly (11); + a switch system (70) configured to keep the second pair (12b) of electrical connections connected to the lithium battery (10), and to connect / disconnect the first pair (12a) of electrical connections of the lithium battery (10 ) as a function of the voltages measured (Vi) at the terminals of each of the accumulator modules (11 i) of the assembly (11). 12. Lithium battery (10) characterized in that it comprises: - a set (11) of accumulator modules (11 i), - a first pair (12a) of electrical connections configured to circulate a first electrical current (la) having an intensity greater than 50 A; - a second pair (12b) of electrical connections configured to circulate a second electrical current (Ib) having an intensity less than the intensity of the first current (la) divided by 2; - the management device (1) according to claim 11. 1/2