Method for forming battery cells

Abstract

A method for forming battery cells comprises electrically coupling battery cells (100) to an electrically active station (10); providing the electrically active station (10) configured to selectively apply to each battery cell (100) first maximum currents or second maximum currents having intensities comprised between 2 5 and 5 times the intensity of the first maximum currents; performing the formation of the battery cells (100) by electrically charging and discharging the battery cells (100), wherein performing the formation comprises applying the first maximum currents to each battery cell (100); performing DC / IR tests on the battery cells (100), wherein performing the DC / IR tests comprises applying the second 0 maximum currents to each battery cell (100); removing the battery cells (100) from the electrically active station (10); wherein performing the formation and performing DC / IR tests are both implemented before removing the battery cells (100) from the electrically active station (10).

Description

[0001] Method for forming battery cells

[0002] DESCRIPTION

[0003] The present invention refers to a method for forming battery cells.

[0004] The present invention finds particular application in the production of secondary batteries, preferably rechargeable lithium batteries. Although specific reference will be made to lithium battery cells in the course of the present disclosure, the teachings of the present invention also apply to the case of other secondary battery cells wherein one of the cell construction processes comprises forming the electrode by passing current therethrough.

[0005] In a lithium battery cell production plant, after mechanical assembly operations of the battery cells, the battery cells must be subjected to electrical operations that lead to electrochemical phenomena within the battery cells such that the anodes are covered by the so-called "Solid Electrolyte Interphase" (SEI). These operations are known in the technical field with the term "formation" of battery cells.

[0006] The battery cell formation operations typically involve a succession of battery cell charge / discharge cycles by applying maximum currents of 0.1 -0.2 C for predetermined times (on the order of 10-30 hours). The magnitude "C" indicates a current value expressed in amperes numerically equal to the cell capacity in Ah (e.g. for a cell capacity of 2 Ah, the magnitude C is 2 A). The currents actually applied, the charge / discharge times and the number of repetitions of the various charge / discharge cycles depend on the type of battery and each battery manufacturer has developed its own "recipe" that allows to best form the electrode surface layer SEI to maximise battery performance. In fact, only if the formation process is performed properly will the electrode surface layer SEI be deposited on the electrodes of the battery, which optimizes the properties of the battery in terms of charge capacity and uniformity of charge / discharge cycles.

[0007] In the Applicant's experience, battery cell formation is performed in a forming apparatus in which battery cell trays, each containing a plurality of battery cells arranged in a matrix pattern, are positioned in respective cubicles. At each cubicle there is provided an electrical contact device comprising a plurality of electrical pins. The electrical contact device is lowered onto the battery cell tray such that the electrical pins contact the poles of each battery cell. A power supply, e.g. arranged above the electrical contact device, supplies energy to each electrical pin so that it can perform charge and discharge cycles.

[0008] Following the formation operations, the formed battery cells are subjected to electrically passive operations, carried out in special resting stations (aging stations) for times of the order of tens or hundreds of hours, in which the cells are allowed to "rest" in arrays of many cubicle levels to allow them to stabilize at specially controlled temperatures.

[0009] Before being sealed inside battery housings, i.e. before being used as an element of a battery, each battery cell is subjected to a DC / IR ("Direct Current Internal Resistance") test. The purpose of this test is to evaluate the correct formation of the electrode surface layer SEI, i.e. to evaluate the actual charge and uniformity capacity of the charge / discharge cycles of the battery cell.

[0010] In the Applicant's experience, the DC / IR test is carried out at a DC / IR test station to which the battery cells are transferred from the aging station. In the Applicant's experience, the DC / IR test station comprises an electrical contact device comprising electrical pins. The electrical contact device is positioned on the battery cell tray such that the electrical pins make contact, preferably at later times, with the poles of each battery cell. A power supply supplies energy to each electrical pin. The DC / IR test is carried out by providing the battery cells with a charging current of the order of magnitude of 1 C or greater in a relatively short time interval, e.g. thirty seconds, by measuring the resulting voltage increase between the poles of the battery cell.

[0011] Modem battery cell production plants, by virtue of the ever-increasing demand for secondary batteries, have reached very high sizes. Suffice it to say that these plants are commonly called Gigafactories and that their sizes are expressed in GWh to indicate the electricity storage capacity expressed in GWh of the batteries produced there in a year. By way of example, a 1 GWh Gigafactory is able to produce enough batteries capable of powering around 15,000 electric vehicles in a single year. There are 50 GWh operating gigafactories.

[0012] In the Applicant's experience, improvements in the logistics for transferring battery cells in such battery cell production plants may have a favourable impact in reducing the complexity and thus the operating costs of the plants.

[0013] The Applicant has noted that the transfer of the battery cells to and from aging stations requires careful planning of both the transfer timing and of the quantities of battery cells that can be transferred. In fact, it must be ensured that the battery cells ending the formation operations can reach the aging stations without obstructing the battery cells that must be transferred from the aging station to the DC / IR test stations and vice versa. If, for example, a battery cell of a first cubicle of an aging station must be transferred to a DC / IR test station while a further battery cell from a formation station has to reach a second cubicle placed in the same array of cubicles or even placed immediately above or below the first cubicle, it is necessary to carefully manage the movement times of the two battery cells. If, for example, battery cells that have finished aging operations have to reach DC / IR test stations but in that instant the receiving capacity of the DC / IR test stations is not sufficient to receive all the battery cells, it is necessary to carefully manage the quantity of battery cells that can be immediately transferred to the DC / IR test stations.

[0014] The Applicant has perceived that if the DC / IR test operations were carried out before sending the battery cells to the aging stations, it would be avoided having to manage the logistics of transferring the battery cells from the aging stations to the DC / IR test stations, as the DC / IR test operations would not be necessary at the end of the aging operations.

[0015] The Applicant has also noted that structurally the formation stations and the DC / IR test stations are similar to each other, in that both stations require electrical pins to be connected to the poles of the battery cells powered by appropriate electrical power supplies.

[0016] The Applicant has therefore found that the formation stations and the DC / IR test stations could be integrated with each other and the aging operations could be performed in the integrated formation and DC / IR test station before sending the battery cells to the aging stations.

[0017] The present invention therefore concerns a method for forming battery cells.

[0018] Preferably, it is provided for electrically coupling a plurality of battery cells to an electrically active station.

[0019] Preferably, it is provided for providing said electrically active station configured to selectively apply to each battery cell first maximum currents or second maximum currents having intensities at least twice the intensity of said first maximum currents.

[0020] Preferably, it is provided for performing a formation of said plurality of battery cells by electrically charging and discharging said battery cells, wherein performing the formation comprises applying said first maximum currents to each battery cell.

[0021] Preferably, it is provided for performing DC / IR tests on said plurality of battery cells, wherein performing DC / IR tests comprises applying said second maximum currents to each battery cell.

[0022] Preferably, it is provided for removing said plurality of battery cells from the electrically active station.

[0023] Preferably, it is provided for performing the formation and performing DC / IR tests are both implemented before removing said plurality of battery cells from the electrically active station.

[0024] The Applicant has found that this allows to perform both the formation and DC / IR tests on battery cells in a same station without having to transfer the battery cells between two physically distinct stations or to and from the same station.

[0025] The Applicant has found that in this way the transport logistics of the battery cells can be simplified.

[0026] The Applicant has also found that in this way it would also be possible to reduce the size of the battery cell production plants, with potential benefits on battery production costs.

[0027] By "battery cell" is meant an assembly composed of at least one anode, one cathode, a possible separator made of dielectric material interposed between anode and cathode and an electrolyte. A battery comprises at least one battery cell.

[0028] By "electrically active station" is meant a station provided with electrical components capable of making electrical power available and transmitting it to a user, in the present case to a plurality of battery cells.

[0029] By "DC / IR test" is meant a test to measure the ohmic outlet resistance of a battery cell (Internal Resistance Test). The DC / IR test is carried out by applying a direct current to the battery cell and measuring the internal voltage drop. The internal voltage drop appears instantaneously upon application of the direct current and therefore this voltage drop is measured immediately after the application of the direct current. The duration of the direct current application is very low, substantially equal to the measurement time of the voltage response of the battery cell. The direct current applied is relatively high and, measured in Amperes, can be numerically of the same order of magnitude as the number expressing the total capacity in Ah of the battery cell. For example, when a battery cell has a capacity of 1Ah, the applied currents are about 1-2 Amperes.

[0030] By "formation" is meant a process in which a battery cell is subjected to charge / discharge / recharge cycles. The currents applied during the charge / discharge / recharge cycles, measured in Amperes, are numerically one order of magnitude less than the number expressing the total capacity in Ah of the battery cell. For example, when a battery cell has a capacity of 1Ah, the maximum currents applied are about 0.1 - 0.2 Amperes. The charge / discharge / recharge cycles are implemented for such a time (e.g., 12-30 hours) as to reach maximum voltage, minimum voltage, and then return the battery cell to a known state of charge, typically 80%.

[0031] By "bi-directional power supply" is meant a power supply device capable of supplying electrical energy to a user device and extracting energy from it, allowing a bi-directional exchange of energy between the user device and the power supply device. In a bi-directional power supply the direction of the electrical energy flow is directed in a controlled manner from the power supply device towards the user device or from the user device towards the power supply device; the possibility that the flow of energy is simultaneously directed from the power supply device towards the user device and from the user device towards the power supply device is never provided.

[0032] By "bi-directional switch" is meant a device that allows the flow of current in both directions between two circuits. A bi-directional switch can be controlled to close in order to allow current to pass in both directions (between the two circuits) and can be controlled to open in order to interrupt the passage of current in both directions; the possibility that in a bi-directional switch the flow of current is exclusively directed towards only one of the two circuits is never provided.

[0033] By "first maximum currents" is meant the maximum current intensity of the formation currents that are used to perform the formation of battery cells. The formation currents vary in intensity during the formation following a current intensity curve that each battery manufacturer considers to be the most appropriate depending on the type of batteries that must be produced. The maximum current intensity reached by the formation currents defines the first maximum currents. By "maximum second currents" is meant the test current intensity used when conducting a DC / IR test. Usually the test current is delivered for a very short time, in the order of seconds or tens of seconds, and is a current of constant intensity over time.

[0034] The present invention may have at least one of the preferred features described below. Such features may be present individually or in combination with each other, unless expressly stated otherwise, in the method of the present invention.

[0035] Preferably, the second maximum currents have an intensity comprised between 2 and 10 times the intensity of said first maximum currents, more preferably comprised between 2 and 8 times the intensity of said first maximum currents, more preferably comprised between 2 and 5 times the intensity of said first maximum currents, more preferably comprised between 2 and 4 times the intensity of said first maximum currents, more preferably comprised between 2.5 and 3.5 times the intensity of said first maximum currents.

[0036] Preferably, each battery cell has a total capacity equal to C Ah.

[0037] Preferably, said first maximum currents are comprised between 0.05 C and 0.4 C and said second maximum currents are comprised between 0.7 C and 2 C, wherein C indicates a current value expressed in Amperes numerically equal to the capacity in Ah of a battery cell.

[0038] Preferably, said first maximum currents are comprised between 0.07 C and 0.35 C, more preferably comprised between 0.08 C and 0.3 C, more preferably comprised between 0.09 C and 0.28 C, for example comprised between 0.1 C and 0.2 C.

[0039] Preferably, said second maximum currents are comprised between 0.8 C and 2 C, more preferably comprised between 0.9 C and 2 C, more preferably comprised between 1 C and 1 .9 C, for example comprised between 1 C and 1 .8 C.

[0040] Preferably, when the action of performing DC / IR tests on a battery cell is implemented, the action of performing the formation on the same battery cell is not implemented.

[0041] Preferably, when the action of performing formation on a battery cell is implemented, the action of performing DC / IR tests on the same battery cell is not implemented. In this way, each battery cell receives at any time only first maximum currents or only second maximum currents, ensuring that each battery cell is subjected only to the formation action or only to the DC / IR test action.

[0042] In some embodiments, preferably while the action of performing the formation is implemented on one battery cell, the DC / IR test action is implemented on another battery cell.

[0043] The Applicant believes that this embodiment can be advantageously implemented when for example on some battery cells the formation is, for whatever reason, completed earlier than on other battery cells. In this case, it is possible to perform DC / IR tests on the battery cells that have completed formation and perform DC / IR tests on the other battery cells at a later time and in particular at the end of their formation.

[0044] In other embodiments, performing the formation is preferably implemented simultaneously on all battery cells of said plurality of battery cells.

[0045] In these embodiments, preferably the formation is started at the same time on all battery cells and is ended at the same time on all battery cells.

[0046] Preferably, performing DC / IR tests is implemented at the end of the action of performing the formation.

[0047] Alternatively, performing DC / IR tests is implemented by interrupting the action of performing the formation.

[0048] In this case, preferably, this interruption is only temporary and at the end of performing DC / IR tests, the action of performing the formation is reactivated.

[0049] In some embodiments, it is provided for performing the DC / IR test on each battery cell several times.

[0050] The Applicant considers that by performing the DC / IR test on each battery cell several times it is possible to monitor or in any case derive directly or indirectly the evolution over time of the formation of the electrode surface layer SEI.

[0051] The Applicant considers that this may allow to obtain an indication representative of the correct formation of the electrode surface layer SEI or, alternatively or in combination, an indication representative of the homogeneity of formation of the electrode surface layer SEI between the battery cells. Preferably it is provided for performing at least one further DC / IR test on each battery cell.

[0052] Preferably, a DC / IR test and a further DC / IR test are temporally separated by a predetermined time interval.

[0053] Preferably, said predetermined time interval is comprised between 5 minutes and 5 hours, more preferably comprised between 5 minutes and 3 hours, more preferably comprised between 5 minutes and 2 hours, more preferably comprised between 5 minutes and 1 hour, more preferably comprised between 10 minutes and 30 minutes.

[0054] Preferably, performing at least one further DC / IR test is implemented by interrupting the action of performing the formation.

[0055] Preferably, this interruption is only temporary and at the end of performing a further DC / IR test, the action of performing the formation is reactivated.

[0056] In these embodiments it may also be provided that at least one DC / IR test is performed on all battery cells at the end of battery cell formation.

[0057] Although the action of performing DC / IR tests can be carried out simultaneously on all battery cells, the Applicant considers it preferable that performing DC / IR tests is not carried out simultaneously on all battery cells of said plurality of battery cells.

[0058] Preferably, performing DC / IR tests comprises simultaneously performing DC / IR tests only on a number M of battery cells comprised between 1 and N-1 , where N is equal to the total number of cells of said plurality of cells.

[0059] Preferably, the number M of battery cells that are simultaneously subjected to the DC / IR test action is less than or equal to N / 2, even more preferably less than or equal to N / 4, even more preferably M is less than or equal to N / 8.

[0060] Preferably, the maximum number of battery cells on which a DC / IR test can be performed simultaneously is equal to the integer that approximates by defect the ratio between the total number of battery cells and a number P, where P is the ratio, approximated in excess, between the second maximum currents and the first maximum currents.

[0061] By way of example, the total number of battery cells is 128, the first maximum currents are 0.27. Amperes and the maximum second currents are 3.2 Amperes. In this numerical example, the ratio between the second maximum currents and the first maximum currents is equal to 11.85. P is therefore equal to 12. The ratio between the total number of battery cells and P is 10.6. Therefore the maximum number of battery cells that can be simultaneously subjected to the DC / IR test action is 10.

[0062] Preferably, performing DC / IR tests comprises: a) simultaneously performing a DC / IR test on M battery cells; b) simultaneously performing a DC / IR test on further M battery cells; repeating the action b) until DC / IR tests are completed on all the plurality of battery cells.

[0063] The Applicant considers it advantageous, for the following reasons, to simultaneously perform DC / IR tests on a maximum number of battery cells equal to the integer that approximates by defect the ratio between the total number of battery cells and a number P, where P is the ratio, approximated in excess, between the second maximum currents and the first maximum currents.

[0064] The Applicant has found that two plurality of bi-directional power supplies could be provided; a first plurality of bi-directional power supplies sized to deliver said first maximum currents and a second plurality of bi-directional power supplies sized to deliver said second maximum currents.

[0065] However, the Applicant noted that in this way the costs and also the sizes of the electrically active station would be high due to the cost necessary to provide the two different plurality of bi-directional power supplies.

[0066] The Applicant has therefore assumed to provide only bi-directional power supplies of the second plurality of bi-directional power supplies, i.e. sized to deliver said second currents, since these bi-directional power supplies would be able to deliver even lower currents than the second maximum currents and therefore would be able to deliver also said first maximum currents.

[0067] However, the Applicant found that also in this case the cost of the electrically active station would not be optimized, as oversized bi-directional power supplies would be used (and therefore more expensive than necessary) compared to the real needs during the formation of the battery cells. The Applicant has perceived that by conveying more formation currents on a single battery cell one would be able to convey a test current on that battery cell, obtaining a high flexibility that allows to pass quickly and reversibly from a formation current to a test current.

[0068] The Applicant has therefore found that only bi-directional power supplies sized to deliver said first maximum currents could be used, by connecting groups of bidirectional power supplies together to also deliver said second maximum currents.

[0069] In this way, the formation of the battery cells can be performed by connecting each bi-directional power supply to a respective battery cell by delivering to each battery cell said first maximum currents and then performing formation simultaneously on all the battery cells. The DC / IR test action instead requires connecting groups of bi-directional power supplies together in order to be able to deliver said second maximum current, not making a respective group of bidirectional power supplies available for each battery cell and therefore not making it possible to perform DC / IR tests on all battery cells simultaneously.

[0070] Therefore, preferably, providing at least one electrically active station comprises providing said electrically active station with a plurality of bi-directional power supplies.

[0071] Preferably, performing DC / IR tests comprises connecting together in parallel groups of said bi-directional power supplies of said plurality of bi-directional power supplies.

[0072] Preferably, each bi-directional power supply of said plurality of bi-directional power supplies is sized to deliver a maximum current equal to or greater than said first maximum currents and less than said second maximum currents.

[0073] Preferably, connecting together in parallel groups of said bi-directional power supplies comprises connecting together in parallel a number G of bi-directional power supplies to achieve a maximum delivery current equal to or greater than said second maximum currents.

[0074] Preferably, said number G of bi-directional power supplies connected in parallel during the execution of the DC / IR test is equal to the integer that approximates in excess the ratio between said second maximum currents and said first maximum currents. Further characteristics and advantages of the present invention will become clearer from the following detailed description of a preferred embodiment thereof, with reference to the appended drawings and provided by way of indicative and non-limiting example, in which:

[0075] Figure 1 is a schematic view of an electrically active station usable in a method for forming battery cells in accordance with the present invention.

[0076] An implementation example of a method for forming battery cells in accordance with the present invention provides for providing at least one electrically active station 10 configured to apply to battery cells 100 selectively first maximum currents comprised between 0.05 C and 0.4 C or second maximum currents comprised between 0.7 C and 2 C.

[0077] The first maximum currents and the second maximum currents are expressed with the value "C", this value is expressed in Amperes and is numerically equal to the total capacity in Ah of each battery cell 100 that must be formed.

[0078] All battery cells 100 that are subjected from time to time to the formation method in accordance with the present invention have the same capacity expressed in Ah.

[0079] If for example a plurality of 64 battery cells 100 are subjected to the formation method, all 64 battery cells have the same capacity expressed in Ah. In the rest of the present description, a value of 2 Ah will be taken as a numerical example of the capacity of each battery cell. In this numerical example, the battery cells 100 that are processed at each implementation of the formation method have a total capacity of 128 Ah. Clearly, this is just a numerical example to better clarify what will follow.

[0080] In accordance with this numerical example, the first maximum currents are comprised between 0.1 Amperes and 0.8 Amperes. The maximum second currents are comprised between 1.4 Amperes and 4 Amperes. By way of example, the first maximum currents are 0.4 Amperes and the second currents are 3.2 Amperes.

[0081] An embodiment example of the electrically active station 10 provides that the electrically active station 10 comprises a main board 11 and an auxiliary board 12. The main board 11 comprises a plurality of outlet electrical terminals 13.

[0082] The auxiliary board 12 comprises a plurality of outlet electrical connectors 14 each of which is configured to be electrically connected to a respective charging connector 101 of each battery cell 100.

[0083] The outlet electrical terminals 13 of the main board 11 are electrically connected to inlet electrical connectors 14a of the auxiliary board 12.

[0084] In the preferred embodiment of the invention, the auxiliary board 12 further comprises a plurality of bi-directional switches 15 located along electrical conduction paths between the inlet electrical connectors 14a and the outlet electrical connectors 14 of the auxiliary board 12.

[0085] The main board 11 further comprises a plurality of bi-directional power supplies 16 which are powered by inlet terminals 17 of the main board 11 on which a supply voltage is made available, which may be a mains voltage or a regulated direct voltage. Each bi-directional power supply 16 is in electrical connection with a respective outlet electrical terminal 13 of the main board 11 .

[0086] The bi-directional power supplies 16 can be buck converters, or boost converters or still converters that can operate as bucks or as boosts depending on the direction of the current, or still converters of another type, suitable for generating a voltage or a modulated current.

[0087] Each bi-directional power supply 16 is sized to deliver a maximum current substantially equal to said first maximum currents, i.e. comprised between 0.05 C and 0.4 C. In the numerical example mentioned above, each bi-directional power supply 16 is sized to deliver 0.4 Amperes. The number of bi-directional power supplies 16 is preferably equal to the maximum number of battery cells that can be simultaneously associated with the electrically active station. In the numerical example mentioned above, the number of bi-directional power supplies is equal to 64.

[0088] The plurality of bi-directional switches 15 comprises first bi-directional switches 15a and second bi-directional switches 15b. Each first bi-directional switch 15a places in electrical connection an inlet electrical connector 14a with a respective outlet electrical connector 14 of the auxiliary board 12. Each second bi-directional switch 15b places in electrical connection two inlet electrical connectors 14a. In other words, each second bi-directional switch 15b connects two bi-directional power supplies 16 to each other in parallel.

[0089] A control unit 18, which may for example be a microprocessor unit, is mounted on board the main board 11 . The control unit 18 is configured to individually open and close both the first bi-directional switches 15a and the second bi-directional switches 15b.

[0090] The method for forming battery cells in accordance with the present invention provides for electrically coupling a plurality of battery cells 100 to the electrically active station 10. Each battery cell 100 is mechanically coupled to the electrically active station 10 with the charge connectors 101 of the battery cells 100 electrically connected with respective outlet electrical connectors 14 of the auxiliary board 12.

[0091] The formation of the battery cells 100 is then performed by electrically charging and discharging the battery cells 100 by applying the first maximum currents to each battery cell 100.

[0092] This action is implemented by closing the first bi-directional switches 15a and opening the second bi-directional switches 15b. In this way, each battery cell 100 can receive and send first currents to and from a respective bi-directional power supply 16.

[0093] In this regard, the control unit 18 switches the first bi-directional switches 15a into the closed position and the second bi-directional switches 15b into the open position. When the first bi-directional switches 15a are in the closed position, each inlet electrical connector 14a is in electrical connection with the respective outlet electrical connector 14. When the second bi-directional switches 15a are in the open position, each inlet electrical connector 14a is not in electrical connection with any other inlet electrical connector 14a.

[0094] In the numerical example mentioned above, in this configuration each battery cell 100 receives a maximum current of 0.4 Amperes.

[0095] During formation or at the end of the formation, a DC / IR test action is implemented.

[0096] In case the DC / IR test action is implemented during formation, the formation is temporarily interrupted on at least M number of battery cells 100 to be subjected to DC / IR test. The formation action is also necessarily interrupted on a further number K of battery cells 100.

[0097] Said number K of further battery cells 100 is preferably a multiple of the number M of battery cells 100 that have to be subjected to DC / IR test.

[0098] In the preferred embodiment of the invention, the number K = (M * P) - M, where P represents an integer given by the ratio, approximated in excess, between the second maximum currents and the first maximum currents.

[0099] In the numerical example mentioned above, P = 3.2 / 0.4 and is therefore equal to 8. In this numerical example, if the number M of battery cells on which the DC / IR test must be performed is equal to 3, then the formation action on these M = 3 battery cells and on further K = 21 battery cells will be interrupted. The total number of battery cells on which the formation action must necessarily be interrupted is therefore 24.

[0100] The maximum number of battery cells 100 on which the DC / IR test can be performed simultaneously is given by the integer which approximates by defect the ratio between the total number of battery cells 100 and the number K. In the numerical example mentioned above (64 battery cells 100), the maximum number of battery cells 100 on which the DC / IR test can be performed simultaneously is 8.

[0101] When the DC / IR test action is carried out simultaneously on a number of battery cells smaller than the maximum number of battery cells on which the DC / IR test can be carried out simultaneously, the battery cells on which the formation action does not necessarily have to be interrupted may continue to be subjected to the formation action or this formation action may also be temporarily interrupted on them. In the numerical example mentioned above, when it is wished to carry out the DC / IR test on 3 battery cells, formation must necessarily be interrupted on 24 battery cells and formation may or may not be interrupted on 40 battery cells.

[0102] At the end of the DC / IR tests, formation is reactivated on the battery cells that had undergone formation suspension.

[0103] In case the DC / IR test action is implemented after formation, no battery cells are subjected to formation during the DC / IR tests.

[0104] Also in this case, the maximum number of battery cells 100 on which the DC / IR test can be performed simultaneously is given by the integer which approximates by defect the ratio between the total number of battery cells 100 and the number K. In the numerical example mentioned above (64 battery cells 100), the maximum number of battery cells 100 on which the DC / IR test can be performed simultaneously is 8.

[0105] Both whether the DC / IR test is carried out by interrupting the formation action, and whether the DC / IR test is carried out at the end of the formation, in the preferred embodiment of the invention, the DC / IR test on any battery cell is carried out by connecting together in parallel a number G of bi-directional power supplies, wherein the number G is equal to the integer that approximates in excess the ratio between the second maximum currents and the first maximum currents. In this way, the second maximum currents can be delivered. In the numerical example mentioned above, the number G is equal to 8.

[0106] To connect in parallel with each other the bi-directional power supplies 16 necessary to carry out a DC / IR test on a single battery cell, the control unit 18 switches a group of second bi-directional switches 15b into a closed position so as to electrically connect in parallel with each other a number of inlet electrical connectors 14a equal to the number of bi-directional power supplies 16 that must be placed in parallel. The control unit 18 also places in the open position all the first bi-directional switches 15a associated with the inlet electrical connectors 14a placed in parallel except for the first bi-directional switch 15a which places the outlet electrical connector 14 in electrical connection with the battery cell to be subjected to DC / IR test. In this way, the battery cell that must be subjected to DC / IR test receives the second maximum current.

[0107] The battery cells 100 connected to the outlet electrical connectors 14 in which the corresponding first bi-directional switches have been switched into the open position are not subjected to either the formation action or the DC / IR test action while carrying out the DC / IR test of the battery cell subjected to DC / IR test.

[0108] The DC / IR tests can be completed on all battery cells 100 according to the modalities described above.

[0109] Only at the end of the formation action and the DC / IR test action the battery cells 100 are decoupled from the electrically active station 10 to be transferred to other stations, for example to aging stations.

Claims

CLAIMS1. Method for forming battery cells comprising: electrically coupling a plurality of battery cells (100) to an electrically active station (10); providing said electrically active station (10) configured to selectively apply to each battery cell (100) first maximum currents or second maximum currents having intensities at least twice the intensity of said first maximum currents; performing a formation at least partial of said plurality of battery cells (100) by electrically charging and discharging said battery cells (100), wherein performing the formation comprises applying said first maximum currents to each battery cell (100); performing DC / IR tests on said plurality of battery cells (100), wherein performing DC / IR tests comprises applying said second maximum currents to each battery cell (100); removing said plurality of battery cells (100) from the electrically active station (10); wherein performing the formation and performing DC / IR tests are both implemented before removing said plurality of battery cells (100) from the electrically active station (10).

2. Method according to any one of the preceding claims, wherein when the action of performing DC / IR tests on a battery cell (100) is implemented, the action of performing the formation on the same battery cell (100) is not implemented and when the action of performing the formation on a battery cell (100) is implemented, the action of performing DC / IR tests on the same battery cell (100) is not implemented.

3. Method according to claim 1 or 2, wherein performing DC / IR tests is not implemented simultaneously on all battery cells (100) of said plurality of battery cells (100).

4. Method according to claim 3, wherein performing DC / IR tests comprises simultaneously performing DC / IR tests only on a number M of battery cells (100) comprised between 1 and N-1 , where N is equal to the total number of battery cells (100) of said plurality of battery cells (100).

5. Method according to claim 4, wherein the maximum number of battery cells(100) on which a DC / IR test can be performed simultaneously is equal to the integer that approximates by defect the ratio between the total number of battery cells (100) and a number P, where P is the ratio, approximated in excess, between the second maximum currents and the first maximum currents.

6. Method according to claim 4 or 5, wherein performing DC / IR tests comprises: a) simultaneously performing a DC / IR test on M battery cells (100); b) simultaneously performing a DC / IR test on further M battery cells (100); repeating the action b) until DC / IR tests are completed on all the plurality of battery cells (100).

7. Method according to any one of the preceding claims, wherein performing the formation is implemented simultaneously on all the battery cells (100) of said plurality of battery cells (100).

8. Method according to any one of claims 1 to 6, wherein while the action of performing the formation is implemented on one battery cell (100), the DC / IR test action is implemented on another battery cell (100).

9. Method according to any one of the preceding claims, wherein performing DC / IR tests is implemented by interrupting the action of performing the formation.

10. Method according to claim 6 and 9, wherein at the end of action a) and before action b) the action of performing the formation is reactivated.11 . Method according to any one of claims 1 to 7, wherein performing DC / IR tests is implemented at the end of the action of performing the formation.

12. Method according to any one of the preceding claims, wherein providing at least one electrically active station (10) comprises providing said electrically active station with a plurality of bi-directional power supplies (16); wherein performing DC / IR tests comprises connecting together in parallel groups of said bi-directional power supplies (16) of said plurality of bi-directional power supplies (16) such that the battery cell that has to be subjected to DC / IR tests receives said second maximum currents.

13. Method according to claim 12, wherein each bi-directional power supply (16) of said plurality of bi-directional power supplies (16) is sized to deliver a maximumcurrent equal to or greater than said first maximum currents and less than said second maximum currents.

14. Method according to any one of the preceding claims, wherein each battery cell (100) has a total capacity equal to C Ah, said first maximum currents being comprised between 0.05 C and 0.4 C and said second maximum currents being comprised between 0.7 C and 2 C, wherein C indicates a current value expressed in Amperes numerically equal to the capacity in Ah of a battery cell (100).

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