FR3044773A1 - METHOD FOR EVALUATING THE HEALTH CONDITION OF AN ELECTROCHEMICAL BATTERY - Google Patents

Abstract

The present invention relates to a method for evaluating the state of health of an electrochemical battery comprising the following steps: a) a step of charging the battery, in a first state of aging (EV1), to a first state of charge, followed by a relaxation time T1; b) a step of measuring a first voltage across the battery (UEV1); c) a step of charging the battery, at a second state of aging (EV2), to a second state of charge, followed by a relaxation time T2; d) a step of measuring a second voltage across the battery (UEV2); e) a step of estimation of the state of health of the battery (SOHE), the state of health of the battery being estimated from the difference between the first and second voltages (UEV1, UEV2).

Description

The invention relates to the general field of electrochemical batteries, and more particularly rechargeable lithium batteries, and especially lithium-ion (Li-ion) batteries.

More specifically, the invention relates to a method for evaluating the state of health of an electrochemical battery.

Today, major efforts are being made to develop batteries that are increasingly secure and have a longer life span. Indeed, battery technology is the best current solution to meet the needs of electrified vehicles.

Unfortunately, the performance of the batteries deteriorate over time and this degradation is highly dependent on the conditions of use but also on the conditions during periods of storage or non-use. Thus, the capacity of the batteries always ends up decreasing over time until the state of health of said battery is critical. Generally, for car manufacturers, when a Li-ion battery has a state of health of less than 80%, it is replaced by a new battery.

The cost of a battery being high, the precise assessment of the state of health of an electrochemical battery is essential for manufacturers developing activities related to electrified cars to ensure optimized management of their fleet, particularly at the management of battery replacement.

Different approaches related to the assessment of the state of health of an electrochemical battery have been developed.

Electrochemical impedance spectroscopy is used in particular to study the aging of batteries through the monitoring of the parameters of an impedance model, as indicated for example by Hang et al in "Electrochemical impedance spectroscopy analysis for lithium-ion battery using Li4Ti50i2 anode ", Journal of

Power Sources, vol.22, pp. 442-447, 2013. Only the process developed is expensive and complex to implement. Other techniques are based on the identification of parameters of a model, for example by Kalman filtering, as indicated by Wang et al in "Multi-parameter battery state estimator based on the adaptive and direct solution of the differential equations ", Journal of Power Sources, vol. 196, pp. 8735-8741, 201 1. These techniques use complex identification algorithms, requiring heavy digital processing. In addition, their implementation presupposes that a fine and precise model of the battery is available.

Furthermore, the document US 2001/0022518 teaches a method for estimating the state of health of a battery from the time required for the charge current of said battery to be divided by two during the voltage phase. constant of a recharge of the type "constant current - constant voltage". According to the document FR 2 977 678, a similar method is disclosed, wherein the state of health is estimated from the time required for the current to cross two thresholds, defined arbitrarily, during said charging phase. at constant voltage.

Another technique consists of a method comprising a first step of recharging a constant current battery until the voltage at its terminals reaches a limit value, a second step of recharging said constant voltage battery and equal to said limiting value, until the charging current falls below a threshold value, and a third step of estimating the state of health of said battery from said charging current measurements acquired during said second charging step at constant voltage. This process is described in WO 2015/049300 and in "Determination of lithium-ion battery state-of-health based on constant-voltage charge phase", Journal of Power Sources, 258 (2014), 218-227, by Eddahech et al. The disadvantage of this method is related to the need for a relatively accurate current measurement. The invention aims to overcome the aforementioned drawbacks and to provide a method for evaluating the state of health of an electrochemical battery that is both simple to implement, reliable and accurate. The subject of the invention is therefore a method for evaluating the state of health of an electrochemical battery comprising the following steps: a) a step of charging the battery, to a first state of aging (EV1), up to at a first state of charge, followed by a relaxation time Ti; b) a step of measuring a first voltage across the battery (Uevi); c) a step of charging the battery, at a second state of aging (EV2), to a second state of charge, followed by a relaxation time T2; d) a step of measuring a second voltage across the battery (Uev2); e) a step of estimating the state of health of the battery (SOHe), characterized in that the state of health of the battery is estimated from the difference between the first and second voltages (Uevi,

UeV2) ·

This method makes it possible to dispense with the use of a complex algorithm and is simple to implement since the estimation of the state of health of the electrochemical battery is based on the measurement of two voltages at its terminals, respectively at two distinct aging states. Other advantages and features of the invention will appear more clearly on examining the detailed description and the accompanying drawings in which: FIG. 1 represents a graph showing the evolution of the state of health of a first technology lithium battery as a function of time, batteries of said technology having been subjected to different conditions of use; FIG. 2 represents a graph showing the evolution of the state of health of a second lithium battery technology as a function of time, batteries of said technology having been subjected to other conditions of use; FIG. 3 represents a graph showing the evolution of the state of health of a third lithium battery technology as a function of time, batteries of said technology having been subjected to different conditions of use; FIG. 4 represents a graph showing the evolution of the state of health of said first lithium battery technology as a function of time, batteries of said technology having been subjected to different conditions of use.

It is specified that the expressions "from ... to ..." used in the present description must be understood as including each of the mentioned terminals.

In the description of the invention, the term "based on" is synonymous with "comprising predominantly".

In the following description, we will describe an example of implementation of a method for evaluating the state of health of an electrochemical battery.

Such a method can advantageously be implemented to control the state of health of a battery of a motor vehicle.

Advantageously, the state of health of the battery is estimated from a relation of formula (I): SOHe = a * (UEvi-UEV2) + b (I) in which: - SOHe designates the state of health drums (%) ; - Uevi denotes the first voltage across the battery at the first aging state EV1 (V); Uev2 denotes the second voltage across the battery at the second aging state EV2 (Y); a is a constant parameter ranging from -10000 to 10000 (% -V-1); b is a constant parameter ranging from 0 to 100 (%).

Thus, during the aging of a battery, the state of health of said battery can be evaluated using a simple linear model, efficient and accurate.

The first state of aging EV1 may refer to the beginning of the life of a battery or a state of referenced aging, known.

The second state of aging EV2 may designate an unknown state of aging.

Thus, preferably, the state of health of said battery is evaluated when the battery is in the second state of aging EV2.

The parameters a and b are constant parameters that depend on the battery whose health status and temperature conditions are to be known when using said battery or during periods of storage or non-use. Thus, a and b can be determined for each battery by measuring the voltages at two known aging states.

Preferably, a is a constant parameter ranging from -5000 to 3000, preferably from -3500 to 1500, more preferably from -2500 to 1200.

Preferably, b is a constant parameter ranging from 50 to 100, preferably from 80 to 100, more preferably from 95 to 100.

According to an example of implementation of a method according to the invention, a step a) of charging the battery, at a first aging state EV1, to a charging state of at least 95%, preferably 98%, more preferably 100%, followed by a relaxation time Ti less than or equal to 2 hours, preferably less than or equal to 30 minutes.

According to a particular embodiment, the state of charge is 100% and the relaxation time Ti is less than or equal to 30 minutes.

We then proceed to a step b) of measuring the first voltage Uevi across the battery, the first aging state EV1.

In a particularly preferred manner, step a) and step b) are two successive steps.

Advantageously, step a) and step b) take place at a temperature Tpi greater than or equal to -30 ° C and less than or equal to 70 ° C.

Then, a step c) of charging the battery is carried out, in a second state of aging EV2, to a state of charge of at least 95%, preferably 98%, more preferably 100%, followed by a relaxation time T2 less than or equal to 2 hours, preferably less than or equal to 30 minutes.

According to a particular embodiment, the state of charge is 100% and the relaxation time T2 is less than or equal to 30 minutes.

Advantageously, the relaxation time Ti is equal to the relaxation time T2.

Then, we proceed to a step d) of measuring the second voltage Uev2 across the battery, to a second aging state EV2.

In a particularly preferred manner, step c) and step d) are two successive steps.

Advantageously, step c) and step d) proceed at a temperature Tp2 greater than or equal to -30 ° C and less than or equal to 70 ° C.

Preferably, the temperature Tpi is equal to the temperature Tp2

According to a particular embodiment of the invention, the electrochemical battery is a lithium battery, preferably a lithium-ion battery.

The present invention is illustrated in a nonlimiting manner by the following examples.

Examples

In the following examples, batteries from three different Li-ion battery technologies have undergone several aging tests under different conditions. The three tested Li-ion battery technologies are respectively "Nickel Manganese Cobalt Technology" (NMC), "Manganese Oxide Technology" (LMO) and "Iron Phosphate Technology" (LFP).

The "Nickel Manganese Cobalt Technology" battery is a battery comprising a graphite-based negative electrode and a nickel-manganese-cobalt oxide-based positive electrode. An example of such an oxide is a material of the formula LiNi 3, Coo, Mn 3, O 3.

The so-called "manganese oxide technology" battery is a battery comprising a negative electrode based on graphite and a positive electrode based on manganese oxide. A material of formula LiMn 2 O 4 or a material of formula LiNiO 4 Mni; 604 are examples of such an oxide.

The so-called "Iron Phosphate" battery is a battery comprising a graphite negative electrode and a positive iron phosphate electrode. A material of formula LiFePO4 is an example of such an oxide.

Before carrying out the aging tests, the batteries from the three technologies were characterized in exactly the same way and an identical pre-cycling protocol was applied six times to each of them. One of the objectives of this pre-cycling test is to make sure that the batteries are not defective.

The batteries of the three technologies were each loaded according to the PCH method indicated below at 25 ° C. Firstly, a first charging phase is performed during which a constant charging current I = 1C, C designating the rated capacity of the battery (indicated by the manufacturer), is supplied to the battery. The voltage U of the battery increases to a maximum value, indicated by the manufacturer, then a second charging phase, up to a state of charge of 100%, is carried out during which the voltage U is kept constant, while current I decreases until I is less than C / 20.

The experimental capacities of the batteries resulting from the three technologies are determined, each time, according to the PCA method indicated below. First, the battery is charged according to the PCH method. The battery is then discharged, at 25 ° C and constant current I = 1C, until reaching its minimum voltage, indicated by the manufacturer. The capacity of the battery is thus determined by amperometric metering. Before subjecting them to aging tests and after each measurement of their capacity, the batteries of the three technologies are put into the state of charge (SOC in%) desired according to the PSOC method indicated below, at 25 ° C. First, the battery is charged according to the PCH method. Then, the battery is discharged at constant current IC for a time Tsoc, Tsoc being equal to Tsoc = 1 heurex (100-SOC) / 100.

Example 1: Calendar aging tests

Lithium-ion batteries have a deterioration in their performance, especially their capacity, over time during periods of non-use. This is called calendar aging. In Example 1 which follows, the calendar aging of the three battery technologies is studied. Following the protocol mentioned above, the batteries are installed in climatic chambers at a given temperature and at a given state of charge.

A. NMC technology batteries

NMC technology identical batteries were subjected to aging tests under four conditions, one battery for each condition.

In the first case, the test was performed at a temperature of 45 ° C and a first NMC battery was charged to a state of charge of 65%. These conditions are called conditions 1.

In the second case, the test was performed at a temperature of 45 ° C and a second NMC battery was charged to a state of charge of 100%. These conditions are called conditions 2.

In the third case, the test was performed at a temperature of 60 ° C and a third NMC battery was charged to a state of charge of 65%. These conditions are called conditions 3.

In the fourth case, the test was performed at a temperature of 60 ° C and a fourth battery of NMC technology was charged to a state of charge of 100%. These conditions are called conditions 4.

For each test, the capacity of the battery is measured over time according to the PCA method. The state of health of the battery is calculated by making the ratio of the capacity measured at a time t on the initial capacity measured at time t = 0.

Figure 1 shows the evolution of the state of health of NMC batteries over time. The curve A1 represents the evolution of the state of health of the battery subjected to the conditions 1. The curve B1 represents the evolution of the state of health of the battery subjected to conditions 2. The curve C1 represents the evolution of the state of health of the battery subject to the conditions 3. The DI curve represents the evolution of the state of health of the battery subject to the conditions 4.

The method for evaluating the state of health of a battery according to the invention was then applied through the relation represented by the formula (I) as defined above, with a = -1500.V'1 and b = 100.

Thus, in FIG. 1, the curve A2 represents the evolution of the state of health of the battery evaluated from the equation of formula (I), for the battery subjected to the conditions 1. The curve B2 represents the evolution the state of health of the battery evaluated from the equation of formula (I), for the battery subject to the conditions 2. The curve C2 represents the evolution of the state of health of the battery evaluated from the relation of formula (I), for the battery subject to the conditions 3. The curve D2 represents the evolution of the state of health of the battery evaluated from the equation of formula (I), for the battery subjected to the conditions 4 .

It is found that the method of evaluating the state of health of a battery according to the invention, applied to the battery NMC technology, gives good results. Indeed, it is observed that the model follows relatively well the experimental curve, and this for all conditions tested.

B. LMO technology batteries

Identical batteries of LMO technology have been subjected to aging tests under four conditions.

In the first case, the test was carried out at a temperature of 30 ° C and a first battery of LMO technology was charged to a state of charge of 100%. These conditions are called conditions 1.

In the second case, the test was carried out at a temperature of 45 ° C and a second battery of LMO technology was charged to a state of charge of 30%. These conditions are called conditions 2.

In the third case, the test was carried out at a temperature of 45 ° C and a third battery of LMO technology was charged to a state of charge of 100%. These conditions are called conditions 3.

In the fourth case, the test was performed at a temperature of 60 ° C and a fourth battery of LMO technology was charged to a state of charge of 100%. These conditions are called conditions 4.

For each test, the capacity of the battery is measured over time according to the PCA method. The state of health of the battery is calculated by making the ratio of the capacity measured at a time t on the initial capacity measured at time t = 0.

Figure 2 shows the evolution of the state of health of LMO batteries over time. The curve H1 represents the evolution of the state of health of the battery subjected to the conditions 1. The curve II represents the evolution of the state of health of the battery subjected to the conditions 2. The curve Jl represents the evolution of the state of health of the battery subjected to the conditions 3. The curve Kl represents the evolution of the state of health of the battery subjected to the conditions 4.

The method for evaluating the state of health of a battery according to the invention was then applied through the relation of formula (I) as defined above, with a = -2500.V'1, and b = 100.

Thus, in FIG. 2, the curve H2 represents the evolution of the state of health of the battery evaluated from the equation of formula (I), for the battery subjected to conditions 1. Curve 12 represents the evolution the state of health of the battery evaluated from the equation of formula (I), for the battery subject to the conditions 2. The curve J2 represents the evolution of the state of health of the battery evaluated from the relation of formula (I), for the conditioned battery 3. The curve K2 represents the evolution of the state of health of the battery evaluated from the relation of formula (I), for the battery subjected to the conditions 4 .

It is found that the method of evaluating the state of health of a battery according to the invention, applied to the battery LMO technology, gives good results. Indeed, it is observed that the model follows relatively well the experimental curve, and this for all conditions tested. Nevertheless, there may be a discrepancy between the model and the experimental curve when the battery is subject to conditions 3. However, a battery must generally be replaced when it displays a state of health of less than 80%. The discrepancy being observed when the state of health is less than 40%, the user will have replaced the battery before the latter displays a state of health as low.

C. LFP technology batteries

The LFP technology battery was subjected to an aging test performed at a temperature of 45 ° C and the LFP battery was charged to a state of charge of 100%.

The capacity of the battery is measured over time. The state of health of the battery is calculated by making the ratio of the capacity measured at a time t on the initial capacity measured at time t = 0.

Figure 3 shows the evolution of the state of health of the LFP battery over time. The curve L1 represents the evolution of the state of health of the battery subjected to the conditions mentioned above.

The method for evaluating the state of health of a battery according to the invention was then applied through the relation of formula (I) as defined above, with a = + 1200V'1 and b = 100 .

Thus, in FIG. 3, the curve L2 represents the evolution of the state of health of the battery evaluated from the equation of formula (I), for the battery subjected to the conditions mentioned above.

It is found that the method of evaluating the state of health of a battery according to the invention, applied to the battery LFP technology, gives good results. Indeed, it is observed that the model follows relatively well the experimental curve.

Example 2: Aging aging tests NMC technology batteries were studied in power cycling according to a particular PCyC cycling process. The PCyC process is defined according to IEC62660-1 under the name "HEV cycling test" and has been adapted to NMC technology batteries. This PCyC power cycling method has been carried out according to two particular protocols.

According to the first protocol, the first step consists in carrying out the PCyC process for 5 days at a given temperature, followed by a second storage step of the battery for 2 days in a climatic chamber at said temperature. Then, both steps are repeated several times.

According to the second protocol, the PCyC process is carried out continuously.

NMC technology batteries have been subjected to cycling aging tests under three conditions.

In the first case, the test was carried out at a temperature of 55 ° C and the PCyC method according to the second protocol was applied to a first battery of NMC technology. These conditions are called conditions 1.

In the second case, the test was performed at a temperature of 55 ° C and the PCyC method according to the first protocol was applied to a second NMC battery. These conditions are called conditions 2.

In the third case, the test was carried out at a temperature of 45 ° C and the PCyC method according to the first protocol was applied to a third battery NMC technology. These conditions are called conditions 3.

For each test, the capacity of the battery is measured during the charging time and the test temperature. Indeed, the capacity of the battery is measured after having discharged it at IC until its minimum voltage before charging it according to the PCH method, at the test temperature. The state of health of the battery is calculated by making the ratio of the capacity measured at a time t on the initial capacity measured at time t = 0.

Figure 4 shows the evolution of the state of health of NMC batteries over time. The curve El represents the evolution of the state of health of the battery subjected to the conditions 1. The curve Fl represents the evolution of the state of health of the battery subjected to the conditions 2. The curve G1 represents the evolution of state of health of the battery subject to the conditions 3.

The method for evaluating the state of health of a battery according to the invention was then applied through the relation of formula (I) as defined above, with a = -1000.V'1 when the temperature is 45 ° C, -1100 ° V'1 when the temperature is 55 ° C, and b = 97.

Thus, in FIG. 4, the curve E2 represents the evolution of the state of health of the battery evaluated from the relation of formula (I), for the battery subjected to the conditions 1. The curve F2 represents the evolution of the state of health of the battery evaluated from the equation of formula (I), for the battery subject to the conditions 2. The curve G2 represents the evolution of the state of health of the battery evaluated from the relation of formula (I), for the battery subject to the conditions 3.

It is found that the method of evaluating the state of health of a battery according to the invention, applied to the battery NMC technology, gives good results. Indeed, it is observed that the model follows relatively well the experimental curve, and this for all conditions tested.

Thus, it has been shown that a simple and reliable method made it possible to evaluate the state of health of a battery with good accuracy.

Claims (13)

A method for evaluating the state of health of an electrochemical battery comprising the following steps: a) a step of charging the battery, at a first state of aging (EV1), to a first state of charge followed by a relaxation time Ti; b) a step of measuring a first voltage across the battery (Uevi); c) a step of charging the battery, at a second state of aging (EV2), to a second state of charge, followed by a relaxation time T2; d) a step of measuring a second voltage across the battery (Uev2); e) a step of estimation of the state of health of the battery (SOHe), characterized in that the state of health of the battery is estimated from the difference between the first and second voltages (Uevi, UeV2) · 2. Method according to claim 1, characterized in that the state of health of the battery is estimated from a relation of formula (I): SOHe = a * (UEvi-UEv2) + b (I), where: - SOHe is the state of health of the battery (%); - Uevi denotes the first voltage across the battery in the first state of aging (EV1) (V); Uev2 denotes the second voltage at the terminals of the battery at the second aging state (EV2) (V); a is a constant parameter ranging from -10000 to 10000 (% -V1); b is a constant parameter ranging from 0 to 100 (%); 3. Method according to claim 1 or 2, characterized in that a is a constant parameter ranging from -5000 to 3000, preferably from -3500 to 1500, more preferably from -2500 to 1200. 4. Method according to any one of the preceding claims, characterized in that b is a constant parameter ranging from 50 to 100, preferably from 80 to 100, more preferably from 95 to 100. 5. Method according to any one of the preceding claims, characterized in that the charging of the battery, during step a), is carried out to a state of charge of at least 95%, preferably 98 %, more preferably 100%. 6. Method according to any one of the preceding claims, characterized in that the charging of the battery during step c) is carried out to a state of charge of at least 95%, preferably 98%. %, more preferably 100%. 7. Method according to any one of the preceding claims, characterized in that the relaxation time Ti is less than or equal to 2 hours, preferably less than or equal to 30 minutes. 8. Method according to any one of the preceding claims, characterized in that the T2 relaxation time is less than or equal to 2 hours, preferably less than or equal to 30 minutes. 9. Process according to any one of the preceding claims, characterized in that the relaxation time Ti is equal to the relaxation time T2. 10. Method according to any one of the preceding claims, characterized in that step a) and step b) take place at a temperature Tpi greater than or equal to -30 ° C and less than or equal to 70 ° C. 11. Process according to any one of the preceding claims, characterized in that step c) and step d) take place at a temperature Tp2 greater than or equal to -30 ° C and less than or equal to 70 ° C. 12. Method according to any one of the preceding claims, characterized in that the temperature Tpi is equal to the temperature Tp2. 13. Method according to any one of the preceding claims, characterized in that the electrochemical battery is a lithium battery, preferably a lithium-ion battery.