Method for determining the chemistry type of a rechargeable electric battery.

Abstract

The invention relates to a method for determining the electrochemical type of a Li-ion cell, comprising the steps of: - measuring the terminal voltage, and if this is between two predetermined values, then: - measuring the cell mass, - injecting a current normalized with respect to ground, between a low and a high voltage value, - determining the charge acceptance value between said low and high values, - comparing the determined charge acceptance value to a predetermined value, and o if this value is greater than the predetermined value, then declaring the cell as belonging to a type NMC or NCA group, suitable for reuse, o if this value is less than the predetermined value, then declaring the cell as belonging to a type LFP group, suitable for reuse. Figure for the abstract: Fig. 6

Description

Title of the invention: Method for determining the chemistry type of a rechargeable electric battery.

[0001] The present invention relates to the field of rechargeable electric batteries, in particular Li-ion.

[0002] Li-ion electric batteries are rechargeable. They use different constituent materials for their anode and cathode. Depending on the choice of these materials, the batteries have different operating voltages.

[0003] We currently distinguish the following 3 families of Li-ion technologies. 1. High voltage or high energy density batteries, which include graphite-based anodes and cobalt-based cathodes, particularly those based on nickel-cobalt-manganese oxide or NMC, or nickel-cobalt-aluminum oxide, or NCA, or LMO for lithium manganese oxide or LiMnO2.

[0004] These batteries have a usage voltage generally between 2.5V and 4.2V, with a nominal voltage generally between 3.6V and 3.7V; 1. Medium voltage, or medium energy density, batteries, which include graphite-based anodes and LiFePO4, or LFP, based cathodes.

[0005] These batteries have a usage voltage generally between 2.0V and 3.6V, with a nominal voltage generally between 3.2V and 3.3V; 1. Low voltage, or low energy density, batteries, which include titanium-based anodes, or LTO, and LFP, NCA or NMC cathodes.

[0006] These batteries have an operating voltage generally between 1.5V and 2.7V, with a nominal voltage generally between 1.9V (with an LFP cathode) and 2.3V (with an NCA cathode).

[0007] Throughout the remainder of the application, the focus is more particularly on distinguishing between high voltage and medium voltage battery chemistries. As such, the names NMC / NCA / LMO / LFP batteries in the description will relate to batteries with an anode based on graphite or carbon, and not titanium.

[0008] The correspondence between the OCV voltage (in V) at the terminals of a Li-ion battery and its state of charge SOC is illustrated in [Fig.5] under charge (curve C) and under discharge (curve D).

[0009] It is clear from [Fig.5] that the sole measurement of OCV voltage at the terminals of a Li-ion battery does not allow to distinguish a NMC / NCA / LMO type cell from an LFP type cell in particular in the area below approximately 3.6 V.

[0010] By simplification, we mean indistinctly the terms “technology”, “chemistry” and “electrochemistry” of a battery.

[0011] By conciseness, we mean indistinctly “battery” and “cell”. Similarly, we use indistinctly the sign “.” and the sign “,” for decimal values.

[0012] Some of the above Li-ion batteries have a similar appearance: similar or even identical shape, similar or even identical volume.

[0013] Thus, typically when they are used or at the end of their life, it can be very difficult to distinguish the different batteries, in particular high voltage / medium voltage, particularly for LFP and NMC / NCA / LMO batteries; in particular in the absence of a label on them, which can happen with used batteries, and which can in fact pose problems of recycling or reuse.

[0014] Furthermore, simply measuring the voltage at the terminals of a battery may be insufficient to determine its chemistry, particularly if the battery is discharged, i.e. has a low state of charge, SOC.

[0015] Typically, if a battery has a voltage greater than or equal to 3.6V, it is very likely that its chemistry is NMC, NCA or LMO. On the other hand, when a battery has a voltage lower than 3.6V, it is possible that its chemistry is LFP, NMC, NCA, LMO...

[0016] Measurements of real and imaginary impedance spectra for different charge states also do not allow for discrimination between technologies.

[0017] In this context, the present invention relates, according to a first of its objects, to a method for determining the electrochemical type of a Li-ion battery cell whose electrochemical type is unknown, with a view to assigning a predetermined group to the cell, each group corresponding to a given electrochemical type of cell and a possible destination of the cells of said group with a view to their recycling or reuse, the method comprising a step consisting of:

[0018] - measure the voltage value across the cell terminals.

[0019] It is essentially characterized in that:

[0020] o if the value of the voltage of the measured voltage is between a first predetermined value and a second predetermined value,

[0021] o then the method further comprises steps consisting of:

[0022] - inject into the cell a predetermined current, between a predetermined low value voltage termination and a predetermined high voltage value,

[0023] - determine the cell charge acceptance value between the low value predetermined voltage value and the predetermined high voltage value,

[0024] - compare the determined load acceptance value to an acceptance value of predetermined load and,

[0025] o if the determined charge acceptance value is greater than the predetermined charge acceptance value, then declare the cell as being of a fourth predetermined group (G4), of type NMC, NCA or LMO, suitable for reuse,

[0026] o if the determined charge acceptance value is less than the predetermined charge acceptance value, then declare the cell as being of a fifth predetermined group (G5), of LFP type, suitable for reuse.

[0027] It is also possible to provide a step consisting of:

[0028] - measure the mass or volume of the cell, and

[0029] - normalize the current injected into the cell relative to the mass or volume of the cell.

[0030] It is also possible to provide steps consisting of:

[0031] - determine the value of the inverse of the internal resistance (RinO of the cell, and if the value of the inverse of the internal resistance of the cell (Rint ') is less than a predetermined threshold value (Rint_ref '), then

[0032] - declare the cell as being of a second predetermined group (G2), of type Degraded Li-ion, suitable for recycling.

[0033] It can be provided that if the value of the voltage of the measured voltage is lower than the first predetermined value, the method then comprises a step consisting of declaring the cell as being of a first predetermined group (Gl), of degraded Li-ion type, capable of being recycled, or of low voltage type.

[0034] It can be provided that if the value of the voltage of the measured voltage is greater than the second predetermined value, the method then comprises a step consisting of declaring the cell as being of the NMC, NCA or LMO type.

[0035] A step can be provided consisting of:

[0036] - determine the value of the inverse of the internal resistance (RinO of the cell, and

[0037] o if the value of the inverse of the internal resistance of the cell (RinO is less than a predetermined threshold value (Rint_ref *), then declare the cell as being of a third predetermined group (G3), of degraded NMC, NCA or LMO type, and suitable for recycling,

[0038] o if the value of the inverse of the internal resistance of the cell (Rint-1) is greater than the predetermined threshold value (Rint_ref'), then declare the cell as being of a fourth predetermined group (G4), of type NMC, NCA or LMO suitable for reuse.

[0039] It is also possible to provide, prior to determining the charge acceptance value, steps for reconditioning the cell consisting of:

[0040] - discharging the cell below a first predetermined threshold value;

[0041] - then recharge the cell at constant current until a second value is reached predetermined threshold;

[0042] - maintain this voltage by gradually lowering the value of the injected current;

[0043] - stop charging when the current value becomes lower than a threshold value predetermined.

[0044] It is also possible to provide, after reconditioning and prior to determining the charge acceptance value, a voltage relaxation step.

[0045] It can be provided that the step of determining the value of the load acceptance comprises a step consisting of:

[0046] - measure the time required for the voltage across the cell to change from predetermined low voltage value to the predetermined high voltage value upon injection of a predetermined current, possibly normalized to the mass or volume of the cell.

[0047] It can be predicted that:

[0048] - the predetermined low voltage value is between 3.55 V and 3.65 V;

[0049] - the predetermined high voltage value is between 3.65 V and 3.8 V;

[0050] - the first predetermined voltage value is 2.3V; and

[0051] - the second predetermined voltage value is 3.6 V.

[0052] It can be expected that the current injected into the cell normalized with respect to the cell mass is equal to 12 mA / g, plus or minus 10%.

[0053] It can be provided that the predetermined charge acceptance value is 0.2 mAh / g, between 3.65 V and 3.7 V and at 12 mA / g of charge current.

[0054] Other characteristics and advantages of the present invention will appear more clearly on reading the following description given by way of illustrative and non-limiting example and made with reference to the appended figures.

[0055] Figures are not to scale.

[0056] DESCRIPTION OF THE DRAWINGS

[0057] [Fig. 1] illustrates a discharge phase, a stabilization phase and a constant current charging phase, applied to an NMC type battery and an LFP type battery,

[0058] [Fig.2] illustrates synchronously with [Fig.l], the voltage response of the NMC type battery and the LFP type battery,

[0059] [Fig.3] illustrates the current applied to the terminals of a cell during a reconditioning phase followed by a charge acceptance phase according to the invention,

[0060] [Fig.4] illustrates, synchronously with [Fig.3], the voltage at the terminals of the cell during the reconditioning phase A followed by the charge acceptance phase B according to the invention,

[0061] [Fig.5] illustrates the correspondence, in charge and in discharge, between the voltage at the terminals of a cell and the state of charge of the cell, for NMC type cells / NCA / LMO and LFP type,

[0062] [Fig.6] illustrates a diagram of an embodiment of the method according to the invention. Detailed description

[0063] [Fig.l] and [Fig.2] are synchronous. As illustrated in [Fig.l] and [Fig.2], which are results of tests carried out by the applicant, the voltage response of an NMC cell during a discharge has a profile similar to the profile of an LFP cell during a discharge (intensity I < 0 in Figures 1 and 2).

[0064] During these tests, after a discharge, the LFP and NMC cells were allowed a resting, relaxation time (intensity 1 = 0 in Figures 1 and 2).

[0065] After the relaxation phase, the LFP and NMC cells were charged with constant current (intensity I > 0 in Figures 1 and 2).

[0066] During charging, the profile of an LFP cell is comparable to the profile of an NMC cell until the maximum charge of the LFP cell is reached, in dotted lines in [Fig.2],

[0067] The present invention cleverly takes advantage of this voltage response characteristic to distinguish and characterize LFP type batteries from NMC, NCA, LMO type batteries.

[0068] A block diagram of one embodiment of the invention is illustrated in [Fig.6].

[0069] It comprises a set of steps which are detailed below.

[0070] First of all, a measurement step 10 is provided. It includes in particular the measurement of the value of the voltage at the terminals of the cell, and the measurement of the mass of the cell.

[0071] A step 20 is then provided for comparing the value of the measured voltage with two reference voltage values: a first predetermined voltage value, and a second predetermined voltage value, different from the first.

[0072] In this case, it is provided that the first predetermined voltage value is equal to 2.3 V plus or minus 10%, and that the second predetermined voltage value is equal to 3.6 V plus or minus 10%.

[0073] 1. If the voltage value of the measured voltage is lower than the first value predetermined (2.3 V), the method then comprises a step of declaring the cell as being of a first predetermined group Gl. In this case, the first predetermined group Gl means that the cell is of the degraded Li-ion type or of the low voltage type, suitable for recycling.

[0074] 2. If the voltage value of the measured voltage is greater than the second value predetermined (3.6 V), the method then comprises a step consisting of declaring the cell as being of the NMC, NCA or LMO type.

[0075] In this case, a step 70 is preferably provided consisting of determining the value of the internal resistance of the cell.

[0076] If the value of the inverse of the internal resistance Rint 1 of the cell is lower than a predetermined threshold value Rint_ref1, then it is possible to declare the cell as being of a third predetermined group G3. In this case, the third group G3 means that the cell is of the degraded NMC, NCA or LMO type and therefore suitable for recycling.

[0077] If the value of the inverse of the internal resistance Rint 1 of the cell is greater than the predetermined threshold value Rint_ref1, then it is possible to declare the cell as being of a fourth predetermined group G4. In this case, the fourth group G4 means that the cell is of the NMC, NCA or LMO type suitable for reuse.

[0078] In this case, it is expected that the predetermined threshold internal resistance threshold value is such that Rint_ref1 = 0.22 S / g, plus or minus 10%.

[0079] 3. If the value of the voltage of the measured voltage is between a first predetermined value and a second predetermined value, then after step 20 of comparing the voltage value, a step 30 can be provided consisting of determining the value of the internal resistance of the cell. Step 30 of determining the value of the internal resistance of the cell is similar, and in this case identical, to step 70 of determining the value of the internal resistance of the cell. In this way, step 30 and step 70 can be a single step, implemented only once, possibly upstream or in parallel with step 10 of measurements.

[0080] In this case, depending on the result of step 30 consisting of determining the value of the internal resistance of the cell:

[0081] If the value of the inverse of the internal resistance Rint 1 of the cell is lower than a predetermined threshold value Rint_ref1, then it is possible to declare the cell as being of a second predetermined group G2. In this case, the second group G2 means that the cell is of the degraded Li-ion type, suitable for recycling.

[0082] In this case, it is expected that the predetermined threshold internal resistance threshold value is such that Rint_ref1 = 0.22 S / g, plus or minus 10%.

[0083] If the value of the inverse of the internal resistance Rint 1 of the cell is greater than the predetermined threshold value Rint_ref1, then it is possible to continue the method according to the invention with a reconditioning step as described below. Reconditioning

[0084] When the value of the inverse of the internal resistance Rint 1 of the cell is greater than the predetermined threshold value Rint_ref1, a step 40 of reconditioning the cell is advantageously provided, illustrated by the dotted zone referenced A in [Fig.4],

[0085] For this purpose, it is first planned to discharge the cell below a first predetermined threshold value.

[0086] The discharge step consists of discharging the cell: - either totally, - either partially, that is to say below a predetermined value, in this case below the low voltage value (2.3 V).

[0087] After discharging, it is planned to recharge the cell at constant current, as illustrated in [Fig.3], until a predetermined threshold voltage value is reached, in this case between 3.6 V and 3.8 V, and preferably equal to 3.7 V, represented by point A1 in [Fig.3] and in [Fig.4].

[0088] It is then planned to maintain this voltage by gradually lowering the value of the injected current, as illustrated between points A1 and A2 in [Fig.3].

[0089] This voltage maintenance step is illustrated by the voltage plateau U between points A1 and A2 in [Fig.4], the plateau corresponding to a constant voltage over time. To maintain the voltage, the battery is charged at a constant voltage, by gradually lowering the value of the current injected during charging, as illustrated between points A1 and A2 in [Fig.3].

[0090] When the current value becomes lower than a predetermined threshold value, it is then planned to stop charging the cell, as illustrated by point A2 in [Fig.3] and [Fig.4].

[0091] When the current value becomes lower than the predetermined threshold value, the battery is considered to be fully charged, and the battery management system (BMS) stops charging it.

[0092] After stopping the charge, there is then a phenomenon of voltage relaxation, as illustrated between points A2 and B1 in [Fig.4].

[0093] The voltage relaxation is such that the voltage at the terminals of the battery decreases naturally to reach a relaxation voltage, which is substantially stable over time.

[0094] A load acceptance step can then be implemented. Load acceptance

[0095] Charge acceptance is defined as the ability of a cell to accept a current between two predetermined voltage values: a low voltage value, in this case the relaxation voltage, and a high voltage value, in this case a target value.

[0096] A step 50 of cell charge acceptance, indistinctly called charge acceptance test, can be provided, illustrated by the dotted zone referenced B in [Fig.4].

[0097] From the voltage relaxation, the charge acceptance measurement allows the characterization of the battery chemistry.

[0098] The tension relaxation time is variable and can range from a few minutes to a few hours. In this case, a relaxation time (between points A2 and B1 in [Fig.4]) greater than or equal to 10 minutes is expected. A predetermined relaxation time or a relaxation time corresponding to a predetermined relaxation voltage, or even to a stabilization of the voltage, can be expected. In this case, a relaxation voltage between 3.55 V and 3.65 V is expected, and more particularly equal to 3.6 V.

[0099] After the voltage relaxation, a predetermined current is injected into the battery, in this case normalized in relation to the weight of the battery.

[0100] The applied current is normalized to the mass of the cell (mA / g), or normalized to the volume of the cell (mA / cm3), the relationship between the mass and volume of a cell being substantially linear.

[0101] Preferably, the current injected for charge acceptance is the same as the current injected for battery charging. Preferably, the standardized injected current is expected to be between 5 mA / g and 15 mA / g, and in this case equal to 12 mA / g with a margin of error of 10%.

[0102] The time required for the voltage at the battery terminals to reach a predetermined target value is then measured, illustrated by point B2 in [Fig.4].

[0103] Preferably, the predetermined target value is between 3.6V and 3.8V, and in this case between 3.65V and 3.7V, so that it does not damage the cell.

[0104] By multiplying the time value by the current value, the charge acceptance of the battery, i.e. the number of Coulombs or mAh / g, can be determined between two voltage values, in this case to go from the relaxation voltage to the target voltage.

[0105] The increase in the voltage at the terminals of the cell, which corresponds to a number of Coulons or mAh / g, i.e. to the value of the charge acceptance of the battery, makes it possible to distinguish 2 electrochemistries, therefore to characterize it, i.e. to determine the electrochemistry of the battery.

[0106] To this end, a step 60 can be implemented consisting of comparing the determined charge acceptance value with a predetermined charge acceptance value, in this case equal to 0.2 mAh / g, plus or minus 10%.

[0107] If the determined charge acceptance value is greater than the predetermined charge acceptance value, then provision is made to declare the cell as being of the fourth predetermined group G4, of type NMC, NCA or LMO, suitable for reuse, as seen previously.

[0108] If the determined charge acceptance value is lower than the predetermined charge acceptance value, then provision is made to declare the cell as being of a fifth predetermined group G5, of LFP type, suitable for reuse.

[0109] Thus, the determination of load acceptance through reconditioning with a current normalized to the mass of the cell makes it possible to distinguish the type of cell when the voltage value at the terminals of the cell is between the first predetermined voltage value (in this case 2.3 V plus or minus 10%), and the second predetermined voltage value (in this case 3.6 V plus or minus 10%).

Claims

Claims

1. Method for determining the electrochemical type of a Li-ion battery cell whose electrochemical type is unknown, with a view to assigning a predetermined group to the cell, each group corresponding to a given electrochemical type of cells and a possible destination of the cells of said group with a view to their recycling or reuse, the method comprising a step consisting of: - measuring the value of the voltage across the terminals of the cell, characterized in that: • if the value of the voltage of the measured voltage is between a first predetermined value and a second predetermined value, • then the method further comprises steps consisting of: • injecting into the cell a predetermined current, between a predetermined low voltage value and a predetermined high voltage value,• determining the charge acceptance value of the cell between the predetermined low voltage value and the predetermined high voltage value, • comparing the determined charge acceptance value with a predetermined charge acceptance value and, • if the determined charge acceptance value is greater than the predetermined charge acceptance value, then declaring the cell as being of a fourth predetermined group (G4), of type NMC, NCA or LMO, suitable for reuse, • if the determined charge acceptance value is less than the predetermined charge acceptance value, then declaring the cell as being of a fifth predetermined group (G5), of type LFP, suitable for reuse.,

2. The method of claim 1, further comprising a step of: measure the mass or volume of the cell, and - normalize the current injected into the cell relative to the mass or volume of the cell.

3. Method according to claim 1 or 2, further comprising steps consisting in: - determining the value of the inverse of the internal resistance (Rint *) of the cell, and if the value of the inverse of the internal resistance of the cell (Rint1) is lower than a predetermined threshold value (Rint_ref *), then - declaring the cell as being of a second predetermined group (G2), of degraded Li-ion type, suitable for recycling.

4. A method according to any preceding claim, wherein if the measured voltage value is lower than the first predetermined value, the method then comprises a step of declaring the cell as being of a first predetermined group (Gl), of degraded Li-ion type, suitable for recycling, or of low voltage type.

5. A method according to any preceding claim, wherein if the voltage value of the measured voltage is greater than the second predetermined value, the method then comprises a step of declaring the cell as being of type NMC, NCA or LMO.

6. Method according to claim 5, further comprising a step consisting of: - determining the value of the inverse of the internal resistance (Rint1) of the cell, and • if the value of the inverse of the internal resistance of the cell (Rint1) is less than a predetermined threshold value (Rint_ref1), then declaring the cell as being of a third predetermined group (G3), of degraded NMC, NCA or LMO type, and capable of being recycled, • if the value of the inverse of the internal resistance of the cell (Rint1) is greater than the predetermined threshold value (Rint_ref *), then declaring the cell as being of a fourth predetermined group (G4), of NMC, NCA or LMO type capable of being reused.

7. Method according to any one of the preceding claims, further comprising, prior to determining the charge acceptance value, steps of reconditioning the cell consisting of: - discharging the cell below a first predetermined threshold value; - then recharging the cell at constant current until a second predetermined threshold value is reached; - maintaining this voltage by gradually lowering the value of the injected current; - stopping the charging when the value of the current becomes lower than a predetermined threshold value.

8. A method according to claim 7, further comprising, after reconditioning and prior to determining the charge acceptance value, a voltage relaxation step.

9. Method according to any one of the preceding claims, in which the step of determining the value of the charge acceptance comprises a step consisting of: - measuring the time necessary for the voltage at the terminals of the cell to change from the predetermined low voltage value to the predetermined high voltage value during the injection of a predetermined current, possibly normalized with respect to the mass or volume of the cell.

10. A method according to any preceding claim, wherein: - the predetermined low voltage value is between 3.55 V and 3.65 V; - the predetermined high voltage value is between 3.65 V and 3.8 V; - the first predetermined voltage value is 2.3 V; and - the second predetermined voltage value is 3.6 V.

11. A method according to any preceding claim, wherein the current injected into the cell normalized to the mass of the cell is equal to 12 mA / g, plus or minus 10%.

12. A method according to any preceding claim, wherein the predetermined charge acceptance value is 0.2 mAh / g, between 3.65 V and 3.7 V and at 12 mA / g of charge current.

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