Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
  • G01R31/392—Determining battery ageing or deterioration, e.g. state of health
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
  • G01R31/3644—Constructional arrangements
  • G01R31/3648—Constructional arrangements comprising digital calculation means, e.g. for performing an algorithm
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
  • G01R31/367—Software therefor, e.g. for battery testing using modelling or look-up tables
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
  • G01R31/382—Arrangements for monitoring battery or accumulator variables, e.g. SoC
  • G01R31/3835—Arrangements for monitoring battery or accumulator variables, e.g. SoC involving only voltage measurements
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
  • H01M10/44—Methods for charging or discharging
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
  • H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
  • H02J7/0047—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with monitoring or indicating devices or circuits
  • H02J7/005—Detection of state of health [SOH]
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
  • H02J7/007—Regulation of charging or discharging current or voltage
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/027—Negative electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
  • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
  • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• TITLE Method for determining the state of health of a lithium-ion battery.
• the invention relates to a method for determining the state of health of a lithium-ion battery.
• the invention also relates to a method for determining a formula for calculating the state of health of a lithium-ion battery.
• the invention also relates to diagnostic equipment comprising hardware and software means capable of implementing such a method for determining the state of health of a lithium-ion battery.
• Lithium-ion batteries are used in many technical fields such as, for example, mobile telephony or the automotive industry. These batteries have a limited lifespan.
• the lifespan of a battery may vary according to its conditions of use, in particular according to its frequency of use and / or according to the charge and discharge currents applied and / or according to its temperatures. 'use.
• the aging of a battery is characterized in particular by a loss of capacity of the battery compared to its new state.
• the state of health of a battery also called SOH according to the Anglicism "State of health" is defined by the ratio of the current capacity of a battery to its nominal capacity, that is to say its capacity. in new condition.
• the state of health of a battery gradually degrades from a value of 100% to a point where it is no longer usable in the given application.
• a commonly used method is to fully charge a battery and then fully discharge it to a zero state of charge. By counting the charges discharged by the battery (that is to say by integrating the discharge current over the entire discharge period) it is possible to calculate the current capacity of the battery.
• This method nevertheless has drawbacks. In particular, it requires a full charge followed by a complete discharge of the battery. However, during its usual use, a battery is rarely fully charged and then discharged before being recharged again. A specific cycle is therefore necessary to calculate the state of health of the battery.
• the aim of the invention is to provide a method for determining the state of health of a lithium-ion battery which overcomes the above drawbacks and improves the determination methods known from the prior art.
• a first object of the invention is a method for determining the state of health of a lithium-ion battery which does not require a complete charge / discharge cycle of the battery.
• a second object of the invention is a method for determining the state of health of a lithium-ion battery which also makes it possible to determine a degradation mode of the battery without damaging it.
• the invention relates to a method for determining the state of health of a lithium-ion battery, the method comprising:
• a fourth step of determining the amplitudes of said peaks - a fifth step of determining a degradation mode of the battery on the basis of the voltages determined during the third step, and on the basis of the amplitudes determined during the fourth,
• the incremental capacity of a battery can be defined by a ratio of a differential of the charge amount of the battery to a voltage differential across the battery terminals.
• the amplitude of one of said peaks determined during the fourth step may be equal to an integral of the incremental capacitance over a voltage range defined around one of the voltages determined during the third step, in particular said voltage range being lower or equal to 50mV and / or greater than or equal to 20mV.
• the second step can comprise the identification of a first peak obtained with a first voltage at the terminals of the battery, of a second peak obtained with a second voltage at the terminals of the battery, and of a third peak obtained with a third voltage at the battery terminals, the first voltage being strictly higher than the second voltage and strictly lower than the third voltage.
• the first step can be carried out by charging the battery with a charging rate less than or equal to C / 5, in particular less than or equal to C / 10, in particular less than or equal to C / 25.
• the battery may include a negative electrode based on graphite or based on lithium titanate, and / or the battery may include a positive electrode based on one of the following materials: - Lithium Iron Phosphate
• the sixth step may comprise a sub-step of selecting a formula for calculating the state of health of the battery on the basis of the degradation mode determined during the fifth step, then a sub-step for calculating the state of health of the battery. state of health of the battery with the selected formula and with an amplitude determined in the fourth step.
• Said formula can be an affine function dependent on an amplitude determined during the fourth step.
• the invention also relates to a method for determining a formula for calculating the state of health of a battery of a lithium-ion battery, the formula being capable of being used in a method of determination such as defined above, the method comprising:
• a battery aging step of a lithium-ion battery - a step of measuring a state of health of the battery by a coulometric analysis
• the invention also relates to diagnostic equipment comprising hardware and software means capable of implementing the determination method as defined above.
• the invention also relates to a computer program product which can be downloaded from a communication network and / or recorded on a data medium readable by a computer and / or executable by a computer, comprising instructions which, when the program is executed by the computer, lead the latter to implement the method as defined above.
• the invention also relates to a computer-readable recording medium comprising instructions which, when they are executed by a computer, lead the latter to implement the method as defined above.
• the invention also relates to a signal from a data medium, carrying the computer program product as defined above.
• FIG. 1 is a schematic view of a lithium-ion battery connected to diagnostic equipment according to one embodiment of the invention.
• FIG. 2 is a block diagram showing the steps of a method for determining the state of health of a battery according to one embodiment of the invention.
• FIG. 3 is a graph showing the evolution of the voltage at the terminals of a lithium-ion cell as a function of its charge, the voltage being expressed in volts and the charge being expressed in ampere-hours.
• FIG. 4 is a graph showing the evolution of the voltage at the terminals of a cell of a lithium-ion battery as a function of an incremental capacity of the cell.
• FIG. 5 is a first graph showing the evolution of the incremental capacity of a cell of a lithium-ion battery as a function of the voltage at the terminals of the cell.
• FIG. 6 is a second graph representing the evolution of the incremental capacity of a cell of a lithium-ion battery as a function of the voltage at the terminals of the cell, the y-axis being normalized.
• FIG. 7 is a graph showing the evolution of the incremental capacity of a cell of a lithium-ion battery as a function of the voltage at the terminals of the cell for different states of health of the cell, the cell undergoing a degradation by loss of active material on a positive electrode.
• FIG. 8 is a graph showing the evolution of the incremental capacity of a cell of a lithium-ion battery as a function of the voltage at the terminals of the cell for different states of health of the cell, the cell undergoing a degradation by loss of active material on a negative electrode.
• FIG. 9 is a graph showing the evolution of the incremental capacity of a cell of a lithium-ion battery as a function of the voltage at the terminals of the cell for different states of health of the cell, the cell undergoing a degradation by loss of active material on the two electrodes.
• FIG. 10 is a graph showing the evolution of the incremental capacity of a cell of a lithium-ion battery as a function of the voltage at the terminals of the cell for different states of health of the cell, the cell undergoing a degradation by loss of cyclable lithium.
• FIG. 11 is a block diagram showing the steps of a method for determining a formula for calculating the state of health of a lithium-ion battery. detailed description
• FIG. 1 schematically illustrates a lithium-ion battery 1.
• the battery 1 can comprise a set of cells 2, also called “accumulators” or “rechargeable batteries”, connected together so as to form an electric voltage generator.
• Each cell 2 comprises a positive electrode, or cathode C, and a negative electrode, or anode A.
• the cathodes C of the different cells are connected directly or indirectly to a positive terminal of the battery.
• the anodes A of the various cells are connected directly or indirectly to a negative terminal of the battery.
• a lithium-ion battery is a battery in which lithium ions can be exchanged reversibly between the positive electrode and the negative electrode.
• the negative electrode can be graphite (LixC6) or lithium titanate (LTO) based.
• the negative electrode therefore comprises an active material which may consist of graphite (LixC6) or consist of lithium (LTO).
• the positive electrode can be based on one of the following materials: - Lithium Iron Phosphate (LFP),
• NMC Nickel Manganese Cobalt Oxide
• NCA Nickel Cobalt Aluminum Oxide
• Battery 1 is connected via its positive terminal and via its negative terminal to diagnostic equipment 3 according to one embodiment of the invention.
• the diagnostic equipment 3 comprises a memory 31 and a microprocessor 32.
• the memory 31 is a computer readable recording medium comprising instructions which, when they are executed by the microprocessor 32, lead the latter to implement a method for determining the state of health of the battery according to one embodiment of the invention.
• the diagnostic equipment 3 is also a battery charger. It is therefore used both to recharge the battery 1 when it is discharged but also to determine its state of health.
• a method for determining the state of health of battery 1 is now described.
• the determination method can be broken down into six steps E1, E2, E3, E4, E5, E6 represented diagrammatically in FIG. 2. These six steps can be carried out successively, that is to say that step is carried out. E1, then step E2, then step E3, then step E4, then step E5 and finally step E6.
• the process can be repeated as often as necessary to update the value of the health condition.
• the state of health of a cell can be defined as the ratio of the current capacity of the cell to its nominal capacity, that is to say its capacity in new condition.
• SOH state of health
• the state of health of a battery comprising several cells can be defined as a function of the state of health of the cells which compose it.
• the method according to the invention can equally well be implemented to directly determine the state of health of a battery comprising several cells or to determine the state of health of an individual cell.
• a function f is determined defining a relationship between an incremental capacitance of the cell and a voltage at the terminals of the cell.
• the incremental capacitance of the cell can be defined as the ratio of a charge quantity differential dQ of the cell to a voltage differential dU across the cell.
• the incremental capacitance can be defined as the derivative of an amount of charge of the cell with respect to a voltage across the cell.
• the function f is the function satisfying the following equation:
• FIG. 3 illustrates a charge curve for cell 2.
• cell 2 is an NMC type cell.
• Such a curve can be established during a full charge of the cell by memorizing the voltage at the terminals of the cell and the charge current.
• the voltage at the terminals of the cell is expressed in volts and is represented on the ordinate.
• the battery charge is expressed in ampere-hours (Ah) and is shown on the abscissa.
• the voltage across the cell is an increasing function of its charge.
• the voltage at the terminals of the battery is between 2.7V (when the battery is completely discharged) and approximately 4.2V ( when the battery is fully charged).
• the battery capacity here is around 16Ah. This curve is therefore obtained by carrying out a full charge of the cell.
• the invention could be adapted to any other type of cell, in particular a cell having a different nominal voltage, and / or a different capacity, and / or a different internal chemical composition.
• FIG. 4 represents the voltage U (expressed in volts) at the terminals of the cell as a function of the incremental capacitance dQ / dll of the cell.
• the curve of Figure 4 can be obtained by performing a derivation operation from the load curve shown in Figure 2.
• FIG. 5 represents the incremental capacitance dQ / dU of the cell as a function of the voltage U (expressed in volts) at the terminals of the cell.
• the curve of FIG. 5 can be obtained by permuting the abscissa axis and the ordinate axis of FIG. 4.
• the curve illustrated in FIG. 5, which can also be called the incremental capacity curve, has a particular shape. , specific to cell 2.
• the incremental capacity curve therefore forms a signature of cell 2.
• the shape of this curve depends on the chemical nature of the cell but also on its state of health.
• step E1 the function f defining the relationship between the incremental capacitance of the cell and the voltage at the terminals of the cell could be established not during a charge of the cell but during its discharge.
• peaks on the function determined during the first step are identified.
• the lithium-ion battery cell incremental capacity curves generally comprise five peaks P1, P2, P3, P4 and P5.
• they include in particular three upward peaks P1, P2, P3, otherwise referred to as “high points” and two downward peaks P4, P5, otherwise referred to as "low points”.
• peak P4 is positioned between peak P1 and peak P2 along the abscissa axis
• peak P5 is positioned between peak P1 and peak P3 along the abscissa axis.
• the three peaks P1, P2 and P3 are identified in particular during this first step.
• the peaks P4 and P5 are not used in the remainder of the process.
• the method could be adapted to exploit other peaks of the function f: for example only one peak or only two peaks among the three peaks P1, P2 and P3.
• the method could also be adapted to exploit the identification of peaks P4 and P5 in addition to or as a replacement for the exploitation of peaks P1, P2 and P3.
• a charge rate equal to C / 5, or slower makes it possible to obtain a good identification of the peaks and subsequently a reliable determination of a mode of degradation of the cell and a reliable determination of the state of health of the cell. the cell.
• the charging rate can thus be less than or equal to C / 5, in particular less than or equal to C / 10, or even less than or equal to C / 25. It is specified that C designates the charge rate necessary to fully charge the cell in one hour. A charge rate of C / N therefore designates a rate which allows the battery to be fully recharged in N hours.
• a full charge of the cell is not necessary, since it is sufficient to cover only the three peaks P1, P2 and P3.
• a load of the cell making it possible to increase the voltage at its terminals from approximately 3.4 volts to approximately 3.9 volts is sufficient.
• a load of about 12 ampere-hours is sufficient to carry out the method when the capacity of the cell is 16 ampere-hours.
• One load corresponds to about 75% of the total capacity of the cell may therefore be sufficient to determine its state of health.
• the amount of charge needed to determine the state of health of the cell can be further reduced from this value of 75% by covering only two peaks, or even one peak among the three peaks. P1, P2 and P3.
• the peak P1 corresponds to the maximum value of the function f. It is reached for a first voltage U1 at the terminals of the cell. According to the example illustrated in Figures 5 and 6, this first voltage is between 3.6 and 3.8 volts.
• the peak P2 corresponds to a local maximum of the function f. It is reached for a second voltage U2 at the terminals of the cell. According to the example illustrated in Figures 5 and 6, this second voltage U2 is between 3.4 and 3.6 volts.
• the peak P3 also corresponds to a local maximum of the function f. It is reached for a third voltage U3 at the terminals of the cell. According to the example illustrated in Figures 5 and 6, this third voltage U3 is between 3.8 and 4.0 volts.
• the first voltage U1 is strictly greater than the second voltage U2 and strictly less than the third voltage U3.
• the peak P4 corresponds to a local minimum of the function f. It is reached for a fourth voltage U4 at the terminals of the cell. According to the example illustrated in Figures 5 and 6, this fourth voltage U4 is between 3.4 and 3.6 volts.
• the fourth voltage U4 is strictly greater than the second voltage U2 and strictly less than the first voltage U1.
• the peak P5 also corresponds to a local minimum of the function f. It is reached for a fifth voltage U5 at the terminals of the cell. According to the example illustrated in Figures 5 and 6, this fifth voltage U5 is close to 3.8 volts.
• the fifth voltage U5 is strictly greater than the first voltage U1 and strictly less than the third voltage U3.
• the function f could include more peaks, in particular in the case where the acquisition of the points of this function would be noisy or disturbed by an external cause.
• Mathematical algorithms such as noise reduction algorithms can be used to identify the peaks P1, P2, and P3 and clearly distinguish them from other local maxima linked to noise or to a disturbance of the function f.
• the abscissa (the voltage U at the terminals of the cell) and the ordinate (the incremental capacitance) of the three peaks P1, P2 and P3 are used to determine a degradation mode of the cell, then for the determination of the state of health of the battery.
• other mathematical methods can be applied to identify peaks.
• a third step E3 three voltages U1, U2, U3 are determined at the terminals of the cell for which the peaks P1, P2, P3 are respectively obtained.
• the three voltages U1, U2 and U3 correspond to the abscissa of the peaks P1, P2 and P3 on the graph shown in Figures 5 and 6.
• a fourth step E4 the amplitudes of the peaks P1, P2 and P3 are determined.
• the amplitude of a peak can be calculated in different ways. According to a first approach, the amplitude of one of said peaks can simply be equal to the value of the incremental capacitance at the level of the peak considered. With reference to the graphs shown in Figures 4 and 5, the amplitude can then simply be read on the ordinate of the graph. In other words, the amplitude of the peaks P1, P2, P3, can be respectively equal to f (U1), f (U2), f (U3). These values are denoted respectively by y1, y2 and y3 in Figure 5.
• the amplitude of one of said peaks can be calculated with an integral of the incremental capacitance over a voltage range PT defined around one of the voltages determined during the third step, c 'that is to say the voltages U1, U2, U3.
• the voltage range PT is advantageously centered on the voltage considered.
• the result of this integral calculation can therefore be equal to the area under the incremental capacitance curve, respectively identified by z1, z2 and z3.
• This calculation method can be both simpler to implement than the method for determining the ordinate of the peaks described above. In addition, this method makes it possible to obtain a result which is less sensitive to possible singular outliers.
• the extent of the voltage range PT considered is advantageously less than or equal to 50 mV and / or greater than or equal to 20 mV. In fact, it has been observed that when the extent of the voltage range is between these two values, the result is a determination of a mode of degradation of the cell and of the state of health of the cell which is particularly reliable.
• a degradation mode of the cell is determined as a function of a comparison of the voltages U1, U2, U3 determined during the third step with first values of reference, and as a function of a comparison of the amplitudes determined during the fourth step with second reference values.
• the mode of degradation of the cell can be identified from a set of previously characterized degradation modes. In the present case, the degradation mode is determined from among four possible degradation modes. These four degradation modes cover a major part of the known aging mechanisms of a cell or a battery.
• FIGS. 7, 8, 9 and 10 illustrate the evolution of the function f characterizing the cell when the latter undergoes a particular mode of degradation. In each of these four figures, several curves have been shown corresponding to several states of health of the cells.
• each of the figures shows four curves corresponding respectively to a state of health equal to 100%, 95%, 90%, 85%.
• the mode of degradation considered the more the state of health of a cell decreases, the more its incremental capacity decreases.
• Each degradation mode corresponds to a scenario of displacement of the incremental capacity peaks and therefore a mathematical law of evolution of the state of health associated either with the height of the peaks or with the regional capacity around them, which gradually decreases. as aging increases.
• FIG. 7 represents the evolution of the incremental capacity of the cell when the cell undergoes degradation by loss of active material on the positive electrode. This mode of degradation can occur in particular in the event of dissolution of transition metals within the cell.
• the state of health of the cell decreases, we see that the amplitude of the peak P1 decreases but the voltage U1 associated with the first peak remains substantially stable.
• the amplitude of the second peak P2 and the voltage U2 associated with the second peak remain globally unchanged.
• the amplitude of the third peak P3 and the voltage U3 associated with the third peak both decrease (the third peak P3 moves down and to the left in the graph of Figure 7).
• FIG. 8 represents the evolution of the incremental capacity of the cell when the cell undergoes degradation by loss of active material on the negative electrode. This degradation mode can in particular occur with one of the following degradation mechanisms:
• the amplitude of the first peak P1 decreases and that the voltage U1 associated with the first peak increases (the first peak P1 moves down and to the right on the graph of figure 8).
• the amplitude of the second peak P2 and the voltage U2 associated with the second peak both decrease.
• the amplitude of the third peak P3 remains substantially stable but the voltage U3 associated with the third peak decreases.
• FIG. 9 represents the evolution of the incremental capacity of the cell when the cell undergoes degradation by loss of active material on the two electrodes.
• the state of health of the cell decreases, it is noted that the amplitude of the first peak P1 decreases and that the voltage U1 associated with the first peak remains stable.
• the amplitude of the second peak P2 decreases and the voltage U2 associated with the second peak remains stable.
• the amplitude of the third peak P3 decreases but the voltage U3 associated with the remainder remains stable.
• FIG. 10 represents the evolution of the incremental capacity of the cell when the cell undergoes degradation by loss of cyclable lithium.
• This mode of degradation can occur in particular in the event of growth or dissolution of the SEI (acronym for the anglicism “Solid Electrolyte Interphase” or passivation film between negative electrode and electrolyte).
• the state of health of the cell decreases, it is observed that the amplitude of the first peak P1 decreases and that the voltage U1 associated with the first peak increases.
• the amplitude of the second peak P2 remains globally stable but the voltage U2 associated with the second increases.
• the amplitude of the third peak P3 remains stable but the voltage U3 associated with the third peak P3 decreases.
• the degradation mode it is possible for example to compare the voltage U 1 corresponding to the peak P1 with a first reference value V1. If the voltage U1 is greater than or equal to the reference value V1, the amplitude of the second peak P2 can be compared with a second reference value V2. If the amplitude of the second peak P2 is greater than or equal to the second reference value V2, it can be deduced that the cell is degraded by loss of cyclable lithium. If the amplitude of the second peak P2 is strictly less than the second reference value V2, it can be deduced that the cell is degraded by loss of active material on the negative electrode.
• the voltage U1 is strictly lower than the first value of reference V1
• the determination of the degradation mode can be based on the comparison of the voltages U1, and / or U2, and / or U3 with first reference values and / or on the comparison of the amplitudes of the peaks P1, and / or P2, and / or P3 (calculated with the first or the second method exposed above) with second reference values.
• a mode of degradation of the cell has therefore been determined. This determination does not require an expertise of the electrodes but only the analysis of the incremental capacity of the cell. It is therefore a non-destructive method of determining the mode of degradation of a cell.
• a sixth step E6 the state of health SOH of the cell is determined as a function of the degradation mode determined during the fifth step and as a function of the amplitudes determined during the fourth step.
• the sixth step E6 can comprise a first sub-step E61 of selecting a formula for calculating the state of health of the cell as a function of the degradation mode determined during the fifth step.
• the sixth step can comprise a second sub-step E62 of calculating the state of health SOH of the cell with the selected formula and with an amplitude determined during the fourth step.
• the formula could be more complex. It could for example be a polynomial function of any order. It could also use the amplitude of two distinct peaks, for example peak P1 and peak P2, or peak P1 and peak P3, or even peak P2 and peak P3. The formula could also use the amplitude of the three peaks P1, P2 and P3.
• the method of determining the state of health of the cell has the advantage of requiring only a partial charge of the cell since it is sufficient that the charge of the cell makes it possible to identify the three peaks P1, P2 and P3. .
• the method could thus be adapted to determine the state of health of the cell based on the use of only two peaks (for example peaks P1 and P2 or peaks P1 and P3), or even of only one of the three. peaks P1, P2, P3.
• the load necessary to implement the invention could be further reduced and could then be less or equal to 50% or even less than or equal to 25% of the total battery capacity.
• formula g could be selected not only as a function of the degradation mode identified but also as a function of the peaks P1, P2 and P3 detected during charging.
• an adequate formula could be used.
• Table 1 illustrates by way of example the calculation formulas used to determine the SOH state of health of cells with different types of positive electrode (Lithium Iron Phosphate (LFP), Lithium Nickel Manganese Cobalt Oxide (NMC) , a mixture of Lithium Cobalt Oxide and Lithium Nickel Cobalt Aluminum Oxide (Blend LCO)).
• LFP Lithium Iron Phosphate
• NMC Lithium Nickel Manganese Cobalt Oxide
• Blend LCO Lithium Nickel Cobalt Aluminum Oxide
• the fourth column are formulas whose variable z is equal to the amplitude of peaks calculated according to the second method exposed above (by calculation of an integral of the incremental capacitance over a voltage range PT around the peak P1, P2 or P3, the voltage range considered, namely 20mV, 30mV or 50mV being indicated in brackets).
• the peak considered (P1, P2 or P3) is indicated in front of the formula.
• Some formulas can be based on the amplitude of the first peak P1.
• Other formulas can be based on the amplitude of the third peak P3.
• Some formulas can include polynomial functions of order two.
• FIG. 11 now illustrates a method for determining a formula g for calculating the state of health of a cell 2 according to one embodiment of the invention. Once determined, this formula g can be recorded in the memory 31 of the diagnostic equipment 3 with a view to implementing the method for determining the state of health of a cell as described above.
• a first step E11 it is possible to determine the function fO defining the relation between the incremental capacitance of the cell and the voltage at the terminals of the cell, when the cell is in the new state, that is to say that is, with 100% health.
• the cell can be aged.
• This aging can be achieved by repeating cycles of charging and discharging the battery under specific conditions. For example, the temperature and / or humidity surrounding the cell, the electric charge and discharge currents of the cell can be adapted in order to cause a particular degradation mode.
• a third step E13 it is possible in a third step E13 to measure the state of health of the cell.
• a method known from the state of the art can then be used, in particular a coulometric analysis. By coulometric analysis, it is understood that the capacity of the battery is calculated by integrating the electric discharge current over the entire discharge period, the cell then being discharged from 100% to 0%.
• a function f1 is again determined defining the relationship between the incremental capacitance of the cell and the voltage at the terminals of the cell.
• the cell therefore has a state of health strictly less than 100%.
• This step can be carried out in parallel with the third step or else during a charging phase of the dedicated cell.
• the temperature and charging speed conditions which are applied during the fourth step E14 are the same as those which will be applied during the first step E1 of the method for determining the state of health of a cell.
• the temperature can be for example fixed at 25 ° C and the charging speed can be for example fixed at C / 25.
• Steps E12, E13 and E14 can then be repeated several times to define the relationship between the incremental capacitance of the cell and the voltage across the cell for different state of health values.
• N a number of functions f 1, f2, ... fN, for as many state of health of the battery.
• the greater the number N the more precise the formula for calculating the state of health that will be determined.
• a fifth step E15 it is possible to identify the peaks P1, P2, P3 on each of the functions fO to fN previously determined. For each of the functions, the voltages U1, U2, U3 for which the peaks are reached are identified, as well as the amplitudes of these peaks according to the first method, according to the second method or even according to the two methods described previously.
• a sixth step E16 it is possible to determine the function g defining the relationship between the state of health of the cell and one or more amplitudes of the peaks P1, P2 and P3.
• a method such as the least squares method could be used.
• the state of health can then be calculated using the following formula [Math 3]
• a physicochemical expertise of the cell is carried out to confirm the mode of degradation that it has undergone.
• a physicochemical expertise of the cell consists in disassembling it and inspecting each of the electrodes.
• a visual analysis or a chemical analysis of the electrodes can then be performed to determine the mode of degradation of the cell.
• different conditions of aging of the cell, during the second step E12 make it possible to cover all the possible modes of degradation of the cell. The determination method which has just been described therefore makes it possible to determine a formula making it possible to simply calculate the state of health.
• This formula is specific to a particular cell design i.e. one type of positive electrode and one type of negative electrode. Preferably, this method is repeated to determine formulas for calculating the state of health of cells having a different design.

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• 2019
  • 2019-10-01 FR FR1910857A patent/FR3101429B1/fr active Active
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