HYBRID POWER STORAGE SYSTEM

Description

TECHNICAL FIELD

[0001] The present invention relates to an electrical energy storage system intended to be connected to an on-board network of a vehicle, the on-board network being associated with an admissible voltage interval.

[0002] The invention also relates to a vehicle carrying such a storage system.

[0003] The invention applies to the field of electrical energy storage, in particular to the field of electrical energy storage for supplying the on-board network of a vehicle. STATE OF THE PRIOR ART

[0004] It is known to install an energy storage system on board a vehicle, such as an automobile. The energy storage system is connected to the vehicle's on-board network and is intended to perform a variety of functions (in all climatic conditions that the vehicle may encounter, including low temperatures), including: maintain, on the on-board network, a sufficiently stable voltage with regard to predetermined stability criteria; provide the energy necessary for the vehicle to operate on standby during prolonged parking phases, i.e. when the vehicle is stopped; provide the energy necessary for the operation of auxiliary equipment when the alternator (in the case of a thermal or hybrid vehicle) or the traction battery (in the case of an electric or hybrid vehicle) is unable to provide said energy; provide the electrical energy necessary to start the engine, in the case of a thermal vehicle.

[0005] Such a storage system is generally recharged by the vehicle's alternator or traction battery, depending on whether it is a thermal, electric or hybrid vehicle.

[0006] By "low temperature", or "cold weather" or "cold", is meant a temperature less than or equal to 0°C (degrees Celsius), for example less than or equal to -20°C, or less than or equal to -30°C.

[0007] It is known to design electrical energy storage systems comprising batteries made using lithium-ion battery cells, in particular Li-ion battery cells comprising metal oxides such as nickel-manganese-cobalt oxide, nickel-cobalt-aluminium oxide, cobalt oxide, manganese oxide, nickel oxide or manganese-nickel oxide.

[0008] Such batteries are, in particular, free of lead, the use of which the legislator intends to ban in the coming years. In addition, even at low temperatures (typically below 0°C), such batteries are capable of delivering a high current, which is advantageous in the event of cold starting.

[0009] However, such Li-ion batteries are not entirely satisfactory.

[0010] In fact, conventional on-board networks, particularly in the automotive sector, are generally networks on which the voltage must be approximately between 12 and 14 V (volts), depending on the operational state of the vehicle. Such networks are also called "12 V networks".

[0011] However, the metal oxide battery cells mentioned above have a nominal voltage of 3.6V to 3.7V and an end-of-charge voltage close to 4.2V.

[0012] For the purposes of the present invention, the term "nominal voltage" of a battery cell means an average voltage observed at the terminals of the battery cell during a discharge phase of said battery cell, from a state of charge for which the voltage at the terminals of the battery cell is maximum (i.e. a maximum state of charge) to a state of charge for which the voltage at the terminals of the battery cell is minimum.

[0013] For the purposes of the present invention, the term "end of charge voltage" of a battery cell means the voltage at the terminals of the battery cell when it is in a maximum state of charge.

[0014] Thus, a battery obtained by connecting four battery cells in series as mentioned above has a nominal voltage of approximately 14.5 V. In this case, such a battery, when connected to a 12 V network, is very lightly charged (typically less than half of its maximum charge). The ratio between the energy actually stored and the maximum storage capacity is very unfavorable, and results in excessive battery size.

[0015] Furthermore, a battery obtained by connecting only three battery cells in series as mentioned above is overloaded as soon as the on-board network voltage exceeds 12.6 V (for example, when the voltage is increased by the alternator or the traction battery), which results in risks of irreversible damage to the battery, or even explosion. Such a voltage increase occurs, for example, during a braking phase of the vehicle with recovery of kinetic energy. According to another example, such a voltage increase occurs when operating equipment with high energy consumption, such as a defrosting device, the purpose of such a voltage increase being to increase the power supplied to the equipment.

[0016] It is also known to produce batteries using battery cells whose positive electrode includes iron phosphate, also called “LFP cells”.

[0017] An LFP cell has a voltage plateau close to 3.3 V. In this case, a battery made by connecting four LFP cells in series has at its terminals, over a wide range of state of charge of its battery cells, typically between 10% and 90%, a voltage close to 13.2 V, compatible with the requirements of a 12 V on-board network.

[0018] In contrast, LFP cells have high internal resistance at low temperatures. Thus, the available power decreases sharply when the temperature drops below 0°C.

[0019] As a result, to meet the requirements imposed by the on-board network, LFP cell-based batteries are generally oversized, meaning that their storage capacity is conditioned by the power they are capable of providing when cold, and that they carry more energy than necessary. This leads to high cost, mass, and bulk.

[0020] Document US2017 / 182 892 A1 discloses a storage system.

[0021] Furthermore, although the series connection of seven Li-ion battery cells comprising metal oxides as mentioned above is likely to provide a voltage compatible with a 24 V network, such cells are not satisfactory, insofar as such a voltage is accessible for a restricted state of charge range of said cells. The ratio between the stored energy and the maximum storage capacity is therefore unfavorable, and results in excessive bulkiness of the battery. An aim of the invention is therefore to propose an electrical energy storage system which is less expensive, less bulky, and more efficient than the conventional storage systems described above. STATEMENT OF THE INVENTION

[0022] To this end, the invention relates to an electrical energy storage system of the aforementioned type, comprising a first connector and a second connector for its connection to the on-board network, a first battery, a second battery, a switch and a member for controlling the state of the switch, the first battery being arranged between the first connector and the second connector, the first battery comprising a plurality of first storage members connected in series, the first battery being configured to have, between its terminals, a first voltage belonging to the admissible voltage range when each of the first storage members has a state of charge in a predetermined state of charge range, for example between 10% and 100%, the second battery being connected in series with the switch between the first connector and the second connector, the second battery comprising a plurality of second storage members connected in series, the second battery being configured to have, between its terminals, a second voltage beyond the admissible voltage range when each of the second storage members is charged, the second battery having, in a predetermined temperature range,an internal resistance lower than the internal resistance of the first battery in the predetermined temperature range, the control member being configured to, when a predetermined condition is verified, control the closing of the switch to allow the flow of electric current between the first terminal and the second terminal through the second battery.

[0023] Indeed, in such a storage system, the first battery is intended to be permanently connected to the on-board network. The first battery is intended to maintain the voltage of the on-board network, particularly in standby mode, and to provide current when hot (i.e. when the temperature is beyond the predetermined temperature range) or at low power, typically less than a hundred watts.

[0024] The second battery is normally disconnected from the on-board network, and is only inserted into the network when a predetermined condition is met. For example, the second battery is connected to the on-board network when the on-board network voltage drops below a predetermined value because the power consumption is high and the storage system temperature is too low.

[0025] In this case, the second battery provides the additional power required for the proper functioning of the on-board network thanks, on the one hand, to a higher no-load voltage than that of the first battery, and, on the other hand, to an internal resistance, in the predetermined temperature range (in particular, at low temperature), lower than that of the first battery.

[0026] Thanks to such operation, the sizing of the storage system according to the invention is easy. More precisely, the sizing of the first battery and the second battery is done independently: the characteristics of the first battery are chosen according to the energy to be supplied to the on-board network and the voltage which must be maintained there; the characteristics of the second battery are chosen according to the power to be supplied to the on-board network when starting and / or when cold.

[0027] The invention therefore proposes an optimal hybrid system, which is very compact, while retaining the ability to operate in cold weather.

[0028] The combination of two such batteries, the first having, when charged, a voltage belonging to an operating range of the on-board network to which the storage system is intended to be connected, and the second having, when charged, a voltage beyond said range, goes against the usual rules for the design of electrical energy storage systems, which reinforces the inventive nature of the invention.

[0029] In fact, the use of a battery which, when charged, has a voltage beyond the operating range of the on-board network is traditionally accompanied by the use of a switching electrical converter to adjust the voltage levels.

[0030] According to other advantageous aspects of the invention, the electrical energy storage system comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations: the controller is configured to store a predetermined voltage threshold, the predetermined condition being verified if the voltage between the first connector and the second connector is less than or equal to the predetermined voltage threshold; the controller is configured to store at least one intermediate voltage in relation to a corresponding duration, the predetermined condition being verified if the voltage between the first connector and the second connector is less than or equal to at least one given stored intermediate voltage for a duration greater than or equal to the associated duration; the control member is, in addition, configured to monitor the temperature of at least one part of the storage system, preferably the temperature of the second battery, the predetermined condition being verified if, in addition, the monitored temperature has a value less than or equal to a predetermined temperature threshold; the storage system further comprises a converter arranged between the first connector and the second battery,and configured to operate as a voltage boost converter for charging the second battery from the first battery and / or from the on-board network; the converter is configured to interrupt the charging of the second battery when the voltage across the second battery reaches a predetermined voltage ceiling; the converter is also configured to operate as a voltage step-down converter for charging the first battery from the second battery; each first storage member comprises a first battery cell, or a plurality of first battery cells connected in parallel, each first battery cell being chosen from: a Li-ion battery cell having a negative electrode comprising graphite and a positive electrode comprising iron phosphate, a Li-ion battery cell with a negative electrode comprising titanate, a lead battery cell,a nickel-zinc battery cell, or a nickel-metal hydride battery cell, each first battery cell preferably having a first nominal voltage less than or equal to 3.5 V; each second storage member comprises a second battery cell, or a plurality of second battery cells connected in parallel, each second battery cell being chosen from: a Li-ion battery cell comprising a negative electrode comprising graphite and / or silicon and a positive electrode comprising at least one metal oxide such as a nickel-manganese-cobalt oxide, a nickel-cobalt-aluminum oxide, a cobalt oxide, a manganese oxide, a nickel oxide, a manganese-nickel oxide, a Li-ion battery cell comprising a negative electrode comprising graphite and a positive electrode comprising iron phosphate,a Li-ion battery cell with a negative electrode comprising titanate, a lead-acid battery cell, a nickel-zinc battery cell, or a nickel-metal hydride battery cell, each second battery cell preferably having a second nominal voltage greater than 3.5 V; the storage system further comprises an auxiliary storage device connected between the first connector and the second connector, the auxiliary storage device comprising a plurality of supercapacitors connected in series; each supercapacitor is a supercapacitor comprising two non-faradaic electrodes, for example based on activated carbon, or a hybrid supercapacitor, such as a hybrid supercapacitor comprising a graphite-based electrode, an activated carbon-based electrode, and an electrolyte comprising a lithium salt,of sodium or potassium; the first battery comprises four first storage members in series, each first storage member comprising a first battery cell, or a plurality of first battery cells connected in parallel, each first battery cell being a Li-ion battery cell comprising a negative electrode comprising graphite and a positive electrode comprising iron phosphate, and, preferably, the second battery comprising at least four second storage members in series, each second storage member comprising a second battery cell, or a plurality of second battery cells connected in parallel, each second battery cell being chosen from: a Li-ion battery cell comprising a negative electrode comprising graphite and / or silicon and a positive electrode comprising at least one metal oxide such as a nickel-manganese-cobalt oxide,a nickel-cobalt-aluminum oxide, a cobalt oxide, a manganese oxide, a nickel oxide, a manganese-nickel oxide, the permissible voltage range comprising the value 13.2 V; the first battery comprises eight first storage members in series, each first storage member comprising a first battery cell, or a plurality of first battery cells connected in parallel, each first battery cell being a Li-ion battery cell comprising a negative electrode comprising graphite and a positive electrode comprising iron phosphate, and, preferably, the second battery comprising at least eight second storage members in series, each second storage member comprising a second battery cell, or a plurality of second battery cells connected in parallel,each second battery cell being chosen from: a Li-ion battery cell comprising a negative electrode comprising graphite and / or silicon and a positive electrode comprising at least one metal oxide such as a nickel-manganese-cobalt oxide, a nickel-cobalt-aluminium oxide, a cobalt oxide, a manganese oxide, a nickel oxide, a manganese-nickel oxide, the admissible voltage range comprising the value 26.4 V.,

[0031] Furthermore, the invention relates to a vehicle comprising a storage system as defined above, the first connector and the second connector being connected to an on-board network of the vehicle.

[0032] According to another advantageous aspect of the invention, the vehicle is a thermal vehicle, the storage system comprising an auxiliary storage device connected between the first connector and the second connector, the auxiliary storage device comprising a plurality of supercapacitors connected in series, the auxiliary storage device being arranged in an auxiliary housing separate from one or more primary housings housing the first battery and the second battery, the auxiliary housing being closer to a starter of the vehicle than the primary housing(s). BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention will be better understood with the aid of the following description, given solely by way of non-limiting example and made with reference to the appended drawings in which: [ Fig. 1 ] there figure 1is a schematic representation of a first embodiment of a storage system according to the invention; and [ Fig. 2 ] there figure 2 is a schematic representation of a second embodiment of a storage system according to the invention. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0034] An electrical energy storage system 2 according to the invention is illustrated by the figure 1 . As will be apparent from the following description, such an energy storage system is a hybrid storage system.

[0035] The storage system 2 is intended to be connected to an on-board network 4 of a vehicle (not shown). The on-board network 4 is associated with an admissible voltage interval. Conventionally, the on-board network 4 is also associated with criteria that the storage system 2 must meet.

[0036] As an illustrative example, storage system 2 must meet the following criteria: store energy of around 200 Wh (Watt hour); continuously supply currents greater than 50 A (Ampere) while maintaining a voltage greater than 11 V at its terminals, even when cold (down to -30°C); supply a starting current with a peak of 500 A and energy of around 2 Wh, even when cold.

[0037] The storage system 2 comprises a first connector 6 and a second connector 8 for its electrical connection to the on-board network 4. The storage system 2 further comprises a first battery 10, a second battery 12, a switch 14 and a member 16 for controlling the state of the switch 14.

[0038] The first battery 10 is arranged between the first connector 6 and the second connector 8, and is capable of storing electrical energy.

[0039] The second battery 12 is connected in series with the switch 14 between the first connector 6 and the second connector 8. The second battery 12 is also capable of storing electrical energy.

[0040] The control member 16 is configured to control the state of the switch 14. More precisely, the control member 16 is configured to control, when a predetermined condition is verified, the closing of the switch 14 to allow the flow of electric current between the first connector 6 and the second connector 8, through the second battery 12. First battery

[0041] The first battery 10 comprises a plurality of first storage members 18 connected in series.

[0042] Each first storage member 18 comprises a first battery cell 20.

[0043] Alternatively, at least one first storage member 18 comprises a plurality of first battery cells 20 connected in parallel. In this case, the first battery cells 20 connected in parallel are preferably identical, or have a similar nominal voltage.

[0044] It follows from the above that the voltage across each first storage member 18 is equal to the voltage across each first battery cell 20 that it comprises.

[0045] The number of first storage members 18 is chosen so that, when each of the first storage members 18 has a state of charge within a predetermined state of charge range, the first battery 10 has, at its terminals, a voltage belonging to the admissible voltage interval. For example, the predetermined state of charge range extends from 10% to 100%.

[0046] According to a preferred embodiment, each first battery cell 20 is a Li-ion battery cell comprising a negative electrode comprising graphite and a positive electrode comprising iron phosphate (called “LFP cell”).

[0047] The use of such LFP cells is advantageous, insofar as they have a voltage plateau of approximately 3.3 V for a state of charge ranging from approximately 10% to approximately 90%, and a voltage of approximately 3 V in the discharged state. As a result, whatever its state of charge, a first battery 10 produced by placing four LFP cells in series has at its terminals a voltage compatible with an on-board network associated with an admissible voltage range of approximately 12 V to approximately 14 V (i.e. a voltage belonging to the admissible voltage range). This is very satisfactory, in particular in comparison with a first battery 10 which would be produced by placing four NMC, NCA, LCO, LMO, LNO or LMNO cells in series (described later); indeed, in this case, the first battery would be compatible with such an on-board network only when its state of charge is less than or equal to 30%.

[0048] As a result, the use of LFP cells for the production of the first battery 10 results in a better stored energy / maximum storage capacity ratio, and therefore a smaller footprint.

[0049] Alternatively, each first battery cell 20 is selected from a Li-ion battery cell with a negative electrode comprising titanate (called “LTO cell”), a lead battery cell, a nickel-zinc battery cell (called “NiZn cell”), or a nickel-metal hydride battery cell (called “NiMH cell”).

[0050] More generally, each first battery cell 20 preferably has a first nominal voltage less than or equal to 3.5 V.

[0051] For example, to satisfy the conditions stated above, the first battery 10 comprises four storage members 18, each comprising seven LFP cells in parallel. In addition, each LFP cell has a storage capacity equal to 2.5 Ah (ampere hour). In this case, when each storage member 18 has a state of charge between 10% and 90%, the first battery 10 provides a voltage equal to 13.2 V, and stores a total energy equal to 231 Wh, which satisfies part of the above criteria.

[0052] Such LFP cells are, for example, cells bearing the commercial reference “26650 M1B” from the manufacturer A123 Systems.

[0053] Optionally, the first battery 10 is arranged in series with a first safety switch 28 between the first connector 6 and the second connector 8.

[0054] In the case of an on-board network 4 whose admissible voltage range includes the value 24 V (for example, an admissible voltage range ranging from 24 V to approximately 28 V), the first battery 10 comprises at least eight first storage members 18 in series. Second battery

[0055] The second battery 12 comprises a plurality of second storage members 22 connected in series.

[0056] Each second storage member 22 comprises a second battery cell 24.

[0057] Alternatively, at least one second storage member 22 comprises a plurality of second battery cells 24 connected in parallel. In this case, the second battery cells 24 connected in parallel are preferably identical, or have a similar nominal voltage.

[0058] It follows from the above that the voltage across each second storage member 22 is equal to the voltage across each second battery cell 24 that it comprises.

[0059] The number of second storage members 22 is chosen so that, when each of the second storage members 22 is charged (i.e. when each second battery cell 24 is charged), the second battery 12 has, at its terminals, a voltage beyond the admissible voltage range.

[0060] According to a preferred embodiment, each second battery cell 24 is a Li-ion battery cell having a negative electrode comprising graphite and / or silicon and a positive electrode comprising at least one metal oxide such as nickel-manganese-cobalt oxide (NMC), nickel-cobalt-aluminum oxide (NCA), cobalt oxide (LCO), manganese oxide (LMO), nickel oxide (LNO), manganese-nickel oxide (LMNO), or a mixture of such oxides.

[0061] The use of such metal oxide cells gives the second battery 12 an internal resistance much lower than the internal resistance of the first battery 10, in particular at low temperatures, for example below 0°C, in particular below -20°C. For example, at a temperature of -30°C, a resistance of approximately 250 mΩ (milliohm) was measured for the first battery 10, and a resistance of approximately 80 mΩ for a second battery 12 of similar size.

[0062] Consequently, with equivalent stored electrical energy, the second battery 12 is capable of delivering, in cold weather, a greater current than the first battery 10.

[0063] Alternatively, each second battery cell 24 is selected from an LFP cell, an LTO cell, a NiZn cell, or a NiMH cell.

[0064] More generally, each second battery cell 24 preferably has a first nominal voltage greater than or equal to 3.5 V. Furthermore, the second battery cells 24 are chosen so that the second battery 12 has, in a predetermined temperature range, an internal resistance lower than the internal resistance of the first battery 10.

[0065] For example, to satisfy the conditions stated above, the second battery 12 comprises four second storage members 22, each comprising fifteen NMC cells in parallel. Each NMC cell has a storage capacity equal to 2.5 Ah, and the voltage at its terminals is limited to 4 V. In this case, the second battery 12 is capable of supplying, at 16 V, an electric current of up to 70 A at -30°C. This is satisfactory with regard to the criteria mentioned above.

[0066] Such NMC cells are, for example, cells with the commercial reference “INR18650-25R” from the manufacturer Samsung.

[0067] Thanks to such characteristics, the storage system of the illustrative example detailed above has a lower mass and volume than a conventional lead-acid battery intended for the same use.

[0068] In the case of an on-board network 4 whose admissible voltage range includes the value 24 V, the second battery 12 preferably comprises at least eight second storage members 22 in series. Switch

[0069] The switch 14 is configured to oppose the flow of current between the second battery 12 and the on-board network 4 when it is in an open (non-conducting) state, and to allow such flow when the switch 14 is in a closed (conducting) state.

[0070] The switch 14 is, for example, a relay. According to another example, the switch 14 is a semiconductor component, such as a MOSFET transistor (from the English " Metal Oxide Semiconductor Field Effect Transistor,for metal-oxide-semiconductor field effect transistor). According to yet another example, the switch 14 is produced by means of two MOSFET transistors in series mounted in opposition, so that the switch 14 is capable of opposing the flow of electric current in both directions. Control body

[0071] As indicated previously, the control member 16 is configured to control the on or off state of the switch 14. In particular, the control member 16 is configured to control the closing (i.e. the switching to an on state) of the switch 14 when a predetermined condition is verified.

[0072] The control unit 16 is also configured to monitor the voltage of the on-board network 4.

[0073] Furthermore, the control member 16 is configured to store a voltage threshold U 0 .

[0074] In this case, the predetermined condition is verified if the control member 16 detects that the voltage of the on-board network 4 has a value less than or equal to the voltage threshold U 0 . Such a situation typically occurs during cold starting, so that the second battery 12 provides the additional power necessary for starting.

[0075] The voltage threshold U 0 is, preferably, the minimum voltage tolerable by the on-board network and / or by the first battery 10.

[0076] Furthermore, the control member 16 is configured to maintain the switch 14 in a non-conducting state when the predetermined condition is not verified.

[0077] In particular, the control member 16 is configured to store a voltage ceiling U max , and to maintain the switch 14 in a non-conducting state when the control member 16 detects that the voltage of the on-board network 4 has a value greater than or equal to the voltage ceiling U max .

[0078] The voltage ceiling U max is, for example, the voltage supplied by the first battery 10 when the first storage devices 18 are charged.

[0079] Controlling the opening of the switch 14 when the voltage of the on-board network 4 has a value greater than or equal to the voltage ceiling U max limits the risk of excessive voltage on the on-board network 4, likely to damage the first battery 10 and / or the auxiliary equipment of the vehicle, which is advantageous.

[0080] Preferably, the control member is also configured to record a plurality of couples (U i , T i ), where U i is an intermediate voltage of rank i, and T i is a corresponding duration of rank i, i being a non-zero natural integer.

[0081] The pairs (U i , T i ) are such that for all successive ranks i, i+1, U i < V i+1 , and T i < T i+1 . Furthermore, for all ranks i, U 0 < U i < U max .

[0082] For example, for an on-board network 4 with an admissible voltage range including the value 12 V, a possible torque is U 1 = 11.5 V and T 1 = 1 s (second).

[0083] In this case, the predetermined condition is also verified if the control member 16 detects that the voltage of the on-board network 4 has a voltage less than or equal to at least one recorded voltage U i, for a duration greater than or equal to the corresponding duration T i.

[0084] In this way, the tolerance of the on-board network 4 to variations in its voltage is taken into account for the connection or not of the second battery 12 to the on-board network 4, which is advantageous.

[0085] Advantageously, the control member 16 is also configured to monitor the temperature of the storage system 2, in particular the temperature of the second battery 12.

[0086] In this case, the predetermined condition is also verified if the control member 16 detects, during operation of the storage system 2, that is to say when it supplies electrical energy, that the monitored temperature has a value less than or equal to a predetermined temperature threshold. Advantageously, the predetermined temperature threshold belongs to the predetermined temperature range and constitutes, for example, the upper limit thereof.

[0087] Alternatively, the predetermined condition is verified if the control member 16 detects that: the voltage of the on-board network 4 has a value less than or equal to the voltage threshold U 0 ; and / or the voltage of the on-board network 4 has a voltage less than or equal to at least one recorded voltage U i, for a duration greater than or equal to the corresponding duration T i ; and / or the monitored temperature has a value less than or equal to a predetermined temperature threshold, during operation of the storage system 2.

[0088] It is advantageous to consider that the predetermined condition is verified when the monitored temperature has a value less than or equal to a predetermined temperature threshold. This results from the fact that, if the second battery 12 has a temperature that is too low, it will have more difficulty fulfilling its function.

[0089] Preferably, the control member 16 is also configured to store a duration T max. In this case, the control member is, in addition, configured to open the switch 14 at the end of a duration T max spent in the closed state.

[0090] This is advantageous because, when the switch 14 is closed, the current supplied by the second battery 12 causes heating linked to the internal resistance of said second battery 12, as well as to the resistance of the wiring between the first and second batteries 10, 12. Controlling the opening of the switch 14 at the end of the duration T max limits the risks of excessive heating of the components of the storage system 2.

[0091] In the case where the first safety switch 28 is present, the control member 16 is advantageously configured to control the opening of the first safety switch 28 in the event of detection of an abnormal situation, and to keep the first safety switch in the closed position otherwise. An abnormal situation is, for example, at the level of the on-board network 4, an overvoltage, an undervoltage, an overcurrent during charging or discharging. According to another example, such an abnormal situation occurs when a monitored temperature is outside a predetermined admissible temperature range.

[0092] Advantageously, the control member 16 is also configured to control the opening of the switch 14 in the event of detection of an abnormal situation. Such an abnormal situation is, for example, at the level of the on-board network 4, an overvoltage, an undervoltage, an overcurrent during charging or discharging. According to another example, such an abnormal situation occurs when a monitored temperature is outside a predetermined admissible temperature range.

[0093] Advantageously, the control member 16 is configured to determine, at any time, the voltage at the terminals of the second battery 12. When said voltage depends strongly on the state of charge of the second battery (which is, for example, the case of batteries comprising NMC, NCA, LMO, LNO, LMNO cells), the control member 16 is configured to determine the state of charge of the second battery 12 from the voltage at its terminals.

[0094] Furthermore, the control member 16 is advantageously configured to, upon each connection of the second battery 12, analyze the voltage jump resulting from such a connection to deduce therefrom the internal resistance of the second battery 12. Such a measurement makes it possible to diagnose the aging state of the second battery 12. In this case, the control member 16 is capable of delivering, from the voltage at the terminals of the second battery 12 and its internal resistance, a signal indicating that the state of the second battery 12 allows it to perform its safety function or not.

[0095] Alternatively, the controller 16 is configured to be connected to a vehicle data network to receive information from the vehicle's computers. In this case, the controller 16 is configured to predict the occurrence of the predetermined condition. Converter

[0096] Advantageously, the storage system 2 further comprises a converter 26 arranged between the first connector 6 and the second battery 12, for example in parallel with the switch 14. The converter 26 is a DC-DC converter.

[0097] The converter 26 is, for example, controlled by the control member 16.

[0098] The converter 26 is configured to recharge the second battery 12 from the on-board network 4 and / or the first battery 10, at a voltage higher than that of the on-board network 4. In this case, the converter 26 is capable of operating as a voltage boost converter.

[0099] In this case, the converter 26 is advantageously configured to establish between the terminals of the second battery 12, during its charging, a charging voltage strictly lower than a maximum voltage of the battery 12. This has the advantageous effect of maximizing the lifetime of the second battery 12.

[0100] Advantageously, the converter 26 is configured to interrupt the charging of the second battery 12 when the voltage across the terminals of the second battery 12 reaches a predetermined voltage ceiling. The predetermined voltage ceiling is chosen to be strictly lower than such a maximum voltage that can be obtained across the terminals of the second battery 12. This has the effect of extending the life of the battery cells of the second battery 12, which is advantageous.

[0101] For example, in the example described above, the maximum voltage that can be obtained at the terminals of each NMC cell is 4.2 V, which corresponds to a maximum voltage at the terminals of the second battery of 16.8 V. The predetermined voltage ceiling is, for example, chosen to be equal to 16 V.

[0102] Advantageously, the converter 26 is also capable of operating as a voltage step-down converter, in particular for recharging the first battery 10 from the second battery 12.

[0103] Preferably, the converter 26 is a low-power converter, from a few watts to a few tens of watts, corresponding to output currents of a few amperes, which limits the manufacturing costs of the storage system 2. More generally, by “low power”, is meant a negligible power compared to the electrical power supplied by the storage system 2 to the on-board network 4.

[0104] For example, in the illustrative example described above, the converter 26 is sized to flow a current not exceeding 2 A.

[0105] Advantageously, the control member 16 is configured so as to control the converter 26 so that the second battery 12 has, at its terminals, an optimal voltage (i.e. an optimal state of charge) over time. Such an optimal voltage is, in particular, a function of the temperature of the second battery 12.

[0106] Indeed, the higher the temperature, the more the aging of the second battery 12 accelerates when it is highly charged. Conversely, the lower the temperature, the greater the need for power from the second battery 12, and the available power is all the greater the more it is charged. Thus, it is desirable for the second battery to be charged more in cold weather, and charged less in hot weather.

[0107] However, too frequent a modification of the state of charge of the second battery 12 is likely to result in energy losses. Also, the control member 16 is preferably not configured to modify, via the converter 26, immediately the state of charge of the second battery 12 at each change in the outside temperature (in particular between day and night), but rather to modify, for example, the state of charge of the second battery 12 as a function of a minimum outside temperature measured during a predetermined observation period, for example between one day and one month.

[0108] A second embodiment of the storage system 102 according to the invention is illustrated by the figure 2 .

[0109] The storage system 102 is distinguished from the storage system 2 of the figure 1only in that it further comprises an auxiliary storage device 50 for electrical energy connected in parallel with the first battery 10, between the first connector 6 and the second connector 8.

[0110] The auxiliary storage device 50 comprises a plurality of supercapacitors 52 in series.

[0111] For example, at least one supercapacitor 52 is a supercapacitor comprising two non-faradic electrodes, for example based on activated carbon.

[0112] According to another example, at least one supercapacitor 52 is a hybrid supercapacitor, such as a hybrid supercapacitor comprising a graphite-based electrode, an activated carbon-based electrode, and an electrolyte comprising a lithium, sodium, or potassium salt.

[0113] Such hybrid supercapacitors have behavior close to that of supercapacitors, while presenting a higher energy density, which allows a reduction in the overall size of the storage system 2.

[0114] For example, to satisfy the conditions stated above, the auxiliary storage device 50 comprises six supercapacitors 52 in series, each having a maximum charging voltage of 2.7 V. In this case, when each battery cell 20 has its nominal voltage across its terminals, each supercapacitor has a voltage of 2.2 V across its terminals. This voltage is significantly lower than the maximum charging voltage, which reduces aging and self-discharge of the supercapacitors 52. For example, the capacitance of each supercapacitor 52 is 1200 F (farad), so that their assembly in series, i.e., the auxiliary storage device, has a capacitance of 200 F.

[0115] Such supercapacitors are, for example, EDLC type supercapacitors (from the English " Electric Double Layer Capacitor ", meaning electric double layer capacitor), bearing the commercial reference "BCAP1200 P270 K04" from the manufacturer Maxwell Technologies.

[0116] The presence of the auxiliary storage device 50 is advantageous, in particular for use on board a thermal or hybrid vehicle. Indeed, in this case, the high current (typically several hundred amperes) required for starting or restarting (case of so-called “microhybrid” vehicles, or, in English, “ stop & start ”) is essentially provided by the supercapacitors, which limits degradation of the first and second batteries 10, 12 which would be due to such a current draw.

[0117] The presence of the auxiliary storage device 50 is also advantageous insofar as the supercapacitors stabilize the voltage of the on-board network 4. In particular, the auxiliary storage device 50 minimizes the amplitude of the voltage front caused by the connection of the second battery 12 to the on-board network 4 when the switch 14 is closed, or the disconnection of the second battery 12 from the on-board network 4 when the switch 14 is opened, or even by the connection / disconnection of any auxiliary equipment to / from the on-board network 4.

[0118] In one variant, the auxiliary storage device 50 is arranged in series with an auxiliary switch 54 between the first connector 6 and the second connector 8. In this case, the control member 16 is configured to control the opening of the auxiliary switch 54 in the event of detection of an abnormal situation, and to maintain the auxiliary switch 54 in the closed position otherwise. Such an abnormal situation is, for example, an overvoltage, an undervoltage, or an overcurrent during charging or discharging at the on-board network 4.

[0119] Preferably, the control member 16 is also configured to control the opening of the auxiliary switch 54 in the event of prolonged phases of non-use. Such a control, on the one hand, reduces the voltage of the supercapacitors 52, which increases their lifespan, and, on the other hand, slows down a discharge of the first battery 10 through the self-discharge of the supercapacitors 52.

[0120] In a variant, and in particular when the storage system 102 is intended to be connected to an on-board network of a thermal vehicle, the auxiliary storage device 50 is arranged in a housing, called “auxiliary housing 53”, separate from one or more housings, called “primary housing(s) 55” housing the first and second batteries 10, 12. In this case, the auxiliary housing 53 is arranged closer to the vehicle starter than the primary housing(s) 55.

[0121] The currents delivered by the auxiliary storage device 50 during starting are much higher than those delivered by the first and second batteries 10, 12, so that the diameters of the conductive wires connecting the auxiliary storage device 50 to the starter are greater. Arranging the auxiliary housing 53 near the starter allows a reduction in their length, which, on the one hand, presents an economic advantage and, on the other hand, reduces losses due to the Joule effect.

[0122] Since supercapacitors are generally capable of tolerating higher temperatures than battery cells, such an arrangement is not detrimental to the proper operation of the storage system 102.

[0123] Furthermore, the first battery 10 and the second battery 12 are preferably placed away from the starter, for example outside the engine hood (in the trunk, under the seats, etc.). Such an arrangement is advantageous, insofar as, in this case, the first battery 10 and the second battery 12 are subjected to a smaller temperature range, which has the effect of increasing their service lives.

Claims

1. Electrical-energy storage system (2), intended to be connected to an onboard network (4) of a vehicle, the onboard network (4) being associated with a permissible voltage range, the storage system (2) comprising a first connector (6) and a second connector (8) for its connection to the onboard network (4), a first battery (10), a second battery (12), a switch (14) and a member (16) controlling the state of the switch (14), the first battery (10) being arranged between the first connector (6) and the second connector (8), the first battery (10) comprising a plurality of first storage members (18) connected in series, the first battery (10) being configured to have, between its terminals, a first voltage belonging to the permissible voltage range when each of the first storage members (18) has a state of charge in a predetermined state of charge range, for example between 10% and 100%, the second battery (12) being connected in series with the switch (14) between the first connector (6) and the second connector (8), the second battery (12) comprising a plurality of second storage members (22) connected in series, the second battery (12) being configured to have, between its terminals, a second voltage beyond the permissible voltage range when each of the second storage members (22) is charged, the second battery (12) having, in a predetermined temperature range, an internal resistance lower than the internal resistance of the first battery (10) in the predetermined temperature range, the control member (16) being configured to, when a predetermined condition is verified, demand the closing of the switch (14) to allow the flow of electrical current between the first terminal (6) and the second terminal (8) through the second battery (12).

2. Storage system (2) according to claim 1, wherein the control member (16) is configured to store a predetermined voltage threshold, the predetermined condition being satisfied if the voltage between the first connector (6) and the second connector (8) is less than or equal to the predetermined voltage threshold.

3. Storage system (2) according to claim 1 or 2, wherein the control member (16) is configured to store at least one intermediate voltage in relation to a corresponding duration, the predetermined condition being satisfied if the voltage between the first connector (6) and the second connector (8) is less than or equal to at least one given stored intermediate voltage for a duration greater than or equal to the associated duration.

4. Storage system (2) according to claim 3, wherein the control member (16) is furthermore configured to monitor the temperature of at least a portion of the storage system (2), preferably the temperature of the second battery (12), the predetermined condition being satisfied if, furthermore, the monitored temperature has a value less than or equal to a predetermined temperature threshold.

5. Storage system (2) according to any one of claims 1 to 4, furthermore including a converter (26) arranged between the first connector (6) and the second battery (12), and configured to operate as a voltage-boost converter for charging the second battery (12) from the first battery (10) and / or the onboard network (4).

6. Storage system (2) according to claim 5, wherein the converter (26) is configured to interrupt charging of the second battery (12) when the voltage at the terminals of the second battery reaches a predetermined voltage ceiling.

7. Storage system (2) according to claim 5 or 6, wherein the converter (26) is also configured to operate as a buck converter for charging the first battery (10) from the second battery (12).

8. Storage system (2) according to any one of claims 1 to 7, wherein each first storage member (18) comprises a first battery cell (20), or a plurality of first battery cells (20) connected in parallel, each first battery cell (20) being selected from: a Li-ion battery cell including a negative electrode comprising graphite and a positive electrode comprising iron phosphate (LFP), a Li-ion battery cell with a negative electrode comprising titanate (LTO), a lead battery cell, a nickel-zinc (NiZn) battery cell, or a nickel-metal hydride (NiMH) battery cell, each first battery cell (20) preferably having a first nominal voltage less than or equal to 3.5 V.

9. Storage system (2) according to any one of claims 1 to 8, wherein each second storage member (22) comprises a second battery cell (24), or a plurality of second battery cells (24) connected in parallel, each second battery cell (24) being selected from: a Li-ion battery cell comprising a negative electrode comprising graphite and / or silicon and a positive electrode comprising at least one metal oxide such as nickel-manganese-cobalt oxide (NMC), nickel-cobalt-aluminium oxide (NCA), cobalt oxide (LCO), manganese oxide (LMO), nickel oxide (LNO), manganese-nickel oxide (LMNO), a Li-ion battery cell including a negative electrode comprising graphite and a positive electrode comprising iron phosphate (LFP), a Li-ion battery cell with a negative electrode comprising titanate (LTO), a lead battery cell, a nickel-zinc (NiZn) battery cell, or a nickel-metal hydride (NiMH) battery cell, each second battery cell (24) preferably having a second nominal voltage greater than 3.5 V.

10. Storage system (2) according to any one of claims 1 to 9, furthermore comprising an auxiliary storage device (50) connected between the first connector (6) and the second connector (8), the auxiliary storage device (50) comprising a plurality of supercapacitors (52) connected in series.

11. Storage system (2) according to claim 10, wherein each supercapacitor (52) is a supercapacitor comprising two non-faradic electrodes, for example based on activated carbon, or a hybrid supercapacitor, such as a hybrid supercapacitor comprising a graphite-based electrode, an activated carbon-based electrode, and an electrolyte comprising a lithium, sodium or potassium salt.

12. Storage system (2) according to any one of claims 1 to 11, wherein the first battery (10) includes four first storage members (18) in series, each first storage member (18) comprising a first battery cell (20), or a plurality of first battery cells (20) connected in parallel, each first battery cell (20) being a Li-ion battery cell including a negative electrode comprising graphite and a positive electrode comprising iron phosphate, and, preferably, the second battery (12) comprising at least four second storage members (22) in series, each second storage member (22) comprising a second battery cell (24), or a plurality of second battery cells (24) connected in parallel, each second battery cell (24) being selected from: a Li-ion battery cell including a negative electrode comprising graphite and / or silicon and a positive electrode comprising at least one metal oxide such as nickel-manganese-cobalt oxide (NMC), nickel-cobalt-aluminium oxide (NCA), cobalt oxide (LCO), manganese oxide (LMO), nickel oxide (LNO) or manganese-nickel oxide (LMNO), the permissible voltage range comprising the value 13.2 V.

13. Storage system (2) according to any one of claims 1 to 11, wherein the first battery (10) includes eight first storage members (18) in series, each first storage member (18) comprising a first battery cell (20), or a plurality of first battery cells (20) connected in parallel, each first battery cell (20) being a Li-ion battery cell including a negative electrode comprising graphite and a positive electrode comprising iron phosphate, and, preferably, the second battery (12) including at least eight second storage members (22) in series, each second storage member (22) comprising a second battery cell (24), or a plurality of second battery cells (24) connected in parallel, each second battery cell (24) being selected from: a Li-ion battery cell including a negative electrode comprising graphite and / or silicon and a positive electrode comprising at least one metal oxide such as nickel-manganese-cobalt oxide (NMC), nickel-cobalt-aluminium oxide (NCA), cobalt oxide (LCO), manganese oxide (LMO), nickel oxide (LNO), or manganese-nickel oxide (LMNO), the permissible voltage range comprising the value 26.4 V.

14. Vehicle comprising a storage system (2) according to one of claims 1 to 13, the first connector (6) and the second connector (8) being connected to an onboard network (4) of the vehicle.

15. Vehicle according to claim 14, the vehicle being a combustion vehicle, the storage system (2) comprising an auxiliary storage device (50) connected between the first connector (6) and the second connector (8), the auxiliary storage device (50) comprising a plurality of supercapacitors (52) connected in series, the auxiliary storage device (50) being arranged in an auxiliary housing (53) separate from one or more primary housing(s) (55) housing the first battery (10) and the second battery (12), the auxiliary housing (53) being closer to a vehicle starter than the primary housing(s) (55).