Battery charging method and system

Abstract

The present invention relates to a method for charging a battery (BAT), comprising the following steps: charging the battery (BAT) by applying a charging voltage (Vmax) to the terminals of the battery (BAT); interrupting the charge when the difference between the charging voltage and the open-circuit voltage (VOCV) of the battery (BAT) is less than a margin ( ) so as to protect the internal resistance of the battery. 2.A method according to claim 1, comprising the following steps, carried out after a first full charge of the battery (BAT): obtaining a measurement of the current (Is) flowing through the battery (BAT) during the application of the charging voltage (Vmax); determining the differential between the charging voltage (Vmax) and the open-circuit voltage (VOCV) of the battery as a function of the measured current (Is) and the internal resistance (λ) of the battery; interrupting the charge as soon as the determined differential is less than the margin (λ) ensuring an open-circuit voltage (VOCV) of the battery (BAT) lower than the charging voltage (Vmax). Figure 1.

Description

Title of the invention: Method and system for charging a battery FIELD OF INVENTION

[0001] The invention relates to monitoring the charge of a battery in order to prevent its degradation over time through charge and discharge cycles. PRIOR TECHNOLOGY

[0002] A battery, in particular of the Lithium-ion type, comprises several cells including a rechargeable electrochemical system to provide a nominal voltage.

[0003] With the development of electrical systems operating by means of a rechargeable battery, in particular electric vehicles, the battery charging time needs to be optimized.

[0004] To charge a battery quickly, high charging voltages must be used. However, the higher the voltages used, the faster the battery degrades during battery usage cycles.

[0005] There is a need to optimize a battery charge that optimizes a compromise between battery life and charging time. Description of the invention

[0006] The invention makes it possible to monitor the charge of a battery in order to prevent its rapid degradation.

[0007] To this end, the invention proposes, according to a first aspect, a method for charging a battery, comprising the following steps:

[0008] charging the battery by applying a charging voltage to the battery terminals;

[0009] interruption of charging when the differential between the charging voltage and the open-circuit voltage of the battery is less than a margin so as to protect the internal resistance of the battery.

[0010] The method according to the first aspect is complemented by the following features alone or in combination:

[0011] - after an initial full charge of the battery, the process includes the steps following: obtaining a measurement of the current flowing in the battery during the application of the charging voltage; determining the differential between the charging voltage and the open-circuit voltage of the battery as a function of the measured current and the internal resistance of the battery; interrupting the charge as soon as the determined differential is less than the margin guaranteeing an open-circuit voltage of the battery lower than the charging voltage;

[0012] - the difference between the charging voltage and the open-circuit voltage of the battery is determined by Riat^s with Is the measured current and R-mt the internal resistance of the battery.

[0013] - the internal resistance of the battery is measured at the first full charge, the battery being fully charged on the first charge when the difference between the charging voltage and the open-circuit voltage of the battery is less than the margin protecting the internal resistance of the battery.

[0014] - the internal resistance of the battery is measured before the application of the voltage of charge, preferably every 10 to 100 charges.

[0015] - the margin is between 10 mV and 250 mV, preferably 100 mV;

[0016] - before charging the battery, a step of measuring the open-circuit voltage at the terminals of the battery, charging begins if the measured voltage is below a threshold from which the internal resistance of the battery is no longer protected.

[0017] - at the first charge, the process comprises the following steps: a) charging of the battery for a maximum duration, preferably between 10 seconds and 100 seconds, typically 60 seconds; b) measurement of the internal resistance of the battery;

[0018] c) measurement of the open-circuit voltage at the terminals at the end of the determined time; d) determination of a differential between the charging voltage and the open-circuit voltage; repetition of steps a) to d) as long as the differential between the charging voltage and the open-circuit voltage of the battery is less than the margin protecting the internal resistance of the battery, the method comprising during step a): e) measurement of the current flowing through the battery during charging; f) determination of the differential between the charging voltage and the open-circuit voltage of the battery as a function of the measured current and the internal resistance of the battery; g) interruption of the charge if the determined differential is less than the margin.

[0019] The invention proposes, according to a second aspect, a charging system comprising a processor for implementing the process according to the first aspect of the invention.

[0020] The invention proposes, according to a third aspect, a computer program product comprising program code instructions for executing the steps of the process according to the first aspect of the invention when the program is executed on a computer. DESCRIPTION OF THE FIGURES

[0021] Other features, objectives and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which:

[0022] Fig. 1 represents an equivalent diagram of a battery and a battery charging system.

[0023] Fig. 2 represents curves of the evolution of the internal resistance of several batteries as a function of an open circuit voltage (or open circuit voltage) measured at the terminals of the battery for different battery charging voltages.

[0024] Figure 3 illustrates a loading method according to a first embodiment of the invention.

[0025] Figure 4 illustrates a loading method according to a second embodiment of the invention.

[0026] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

[0027] Figure 1 illustrates a rechargeable battery BAT (e.g., Lithium-Ion) using a battery charging system 1 comprising a processor 2 configured to implement a charging process described below. The charging system 1 is preferably integrated within a battery charger, for example, a battery charger for an electric vehicle. The charging system 1 also includes a memory 3 for storing various values ​​used during the charging process. The processor 2 is configured to obtain several measurements, including a measurement of the open-circuit voltage VOcv (i.e., the voltage when the battery is disconnected from any circuit) across the battery terminals, characteristic of the state of charge of the battery BAT, and a measurement of the current Is flowing through the battery BAT.Processor 2 is also configured to control the application of a Vmax charging voltage to the terminals of battery BAT, and to process the various measurements and more generally to control the charging of battery BAT.

[0028] The idea of ​​the method of the invention is to protect the battery BAT to prevent its internal resistance, denoted Rint, from degrading during charging. Indeed, it has been observed that when the open-circuit voltage VOcv across the battery terminals approaches the charging voltage Vmax (or setpoint), the internal resistance Rint degrades, impacting the battery's lifespan. This phenomenon is illustrated in [Fig. 2], which shows curves of the evolution of the internal resistance Rint as a function of the open-circuit voltage Vocv measured across the battery terminals for several batteries. Each curve corresponds to a charging voltage Vmax (4.1 V, 4.2 V, 4.3 V) for different batteries. According to these curves, it can be seen that the internal resistance Rint increases almost exponentially as the open-circuit voltage VOcv approaches the charging voltage Vmax. The more this internal resistance increases, the faster the battery degrades.

[0029] Consequently, it is proposed to prevent the open-circuit voltage Vocv from reaching the charging voltage Vmax during battery charging. Thus, a margin 7 = Vmax ■ Vocv guarantees an open-circuit voltage VOcv measured at the battery terminals. A margin of error lower than the maximum charging voltage (Vmax) is defined. This margin depends on the battery and is typically < 100 mV for a solid-state battery. Monitoring the open-circuit voltage (Vocv) is therefore relevant for optimizing battery charging. This open-circuit voltage can be monitored either by direct measurement or by measuring the current, according to one of the embodiments described below.

[0030] According to a first embodiment, illustrated in Figure 3, at the beginning of the process, the system measures the open-circuit voltage VOcv across the battery terminals (step E0). If the potential difference between the charging voltage Vmax and the open-circuit voltage VOcv is less than the margin % (step E01), then charging begins by applying the charging voltage Vmax (step E02) for a predetermined duration (X s), typically between 10 and 100 seconds, preferably 60 seconds. The charging voltage Vmax is typically between 4.1 V and 10 V but may vary depending on the battery type. At the end of this duration, the open-circuit voltage VOcv across the battery terminals (step E0) is measured, and charging continues as long as the potential difference between the charging voltage Vmax and the open-circuit voltage VOcv is less than the margin; otherwise, it terminates.According to this first embodiment, the internal resistance of the battery is protected and it is necessary to interrupt the charge to measure the open-circuit voltage Voev-.

[0031] According to a second embodiment, illustrated in [Fig.4], to improve the charging time, the current flowing in the battery is measured to avoid having to interrupt the charge in normal use after the first charge.

[0032] According to this second embodiment, at the beginning of the process, the system detects (step E1) whether it is the first charge of the battery (i.e., that it has never been charged) and measures the open-circuit voltage VOcv across the battery terminals (step E0). The detection of the first charge depends on the type of battery. Upon the first charge, the battery undergoes conditioning (step E2), which consists of fully charging the battery, i.e., up to the charge limit such that the potential difference between the charging voltage and the open-circuit voltage VOcv is less than the margin. To do this, the charging voltage is applied (step E21) to the battery for a maximum duration (X s), for example, between 10 and 100 seconds, preferably 60 seconds. At the end of this period, the application of the charging voltage Vmax is interrupted and the internal resistance Rint of the battery is measured as well as the open-circuit voltage VOcv (step E22 and E23).These periods of charging and measuring resistance and voltage are repeated as long as the potential difference between the charging voltage and the open-circuit voltage is less than the margin \ this difference being . calculated and compared to the margin (step E24). As soon as this potential difference exceeds the margin, the conditioning stops.

[0033] During charging, the current Is flowing through the battery is also measured (step E25), and the ratio of the measured current to the last measured internal resistance Rint of the battery is determined (step E26). If this ratio is less than the margin 7, then charging at the maximum voltage Vmax is stopped; otherwise, it continues as long as this ratio remains less than the margin 7 and as long as the time X s has not elapsed (step E27). This protects the internal resistance Rint of the battery during the charging period.

[0034] During the subsequent charging steps (step E3), the state of charge is first checked by measuring the open-circuit voltage VOcv (step E31). If the potential difference between the charging voltage and the open-circuit voltage VOcv is less than the margin, then charging starts; otherwise, charging does not proceed, and the process is interrupted.

[0035] Before starting the charging process, a measurement of the battery's internal resistance is taken and this value is stored (step E32). This measurement is not always necessary because the charging system can use the measurement of the battery's internal resistance after the first charge. This is particularly true if this resistance does not change over time. Of course, if this measurement is not available, then the internal resistance is measured. This measurement can be taken periodically every N charging cycles, where N is between 10 and 100.

[0036] Next, the charging voltage is applied (step E33) and during charging the current Is flowing through the battery is measured (step E34). Then, the ratio of the measured current to the internal resistance of the battery is determined (step E35), and if this ratio is less than the margin, then charging is stopped; otherwise, it continues as long as this ratio is less than the margin.

[0037] In other words, it is verified if Is < ylRint- Indeed, when a voltage is applied to a battery, which has a certain open-circuit voltage VOcv, it is the difference between VOcv and Vmax that determines the current and not directly Vmax. Consequently, the ratio between the internal resistance Rint of the battery and the current Is flowing in the battery is given by the margin 7. This is also because the open-circuit voltage VOcv is measured with respect to ground and not with respect to the battery potential. The open-circuit voltage VOcv and the voltage Vmax are referenced with respect to ground and not to each other (V (is not a potential difference, but an absolute value).

Claims

Demands

1. Method of charging a battery (BAT), comprising the following steps: charging (E01, E21, E33) the battery (BAT) by applying (E02, E21, E33) a charging voltage (Vmax) to the terminals of the battery (BAT); interrupting (E01, E31, E35) the charging when the differential between the charging voltage and the open-circuit voltage (VOcv) of the battery (BAT) is less than a margin (^) so as to protect the internal resistance of the battery.

2. A method according to claim 1, comprising the following steps, carried out after a first full charge (E2) of the battery (BAT): obtaining (E34) a measurement of the current (Is) flowing in the battery (BAT) during the application of the charging voltage (Vmax); determining (E35) the differential between the charging voltage (Vmax) and the open-circuit voltage (VOcv) of the battery (BAT) as a function of the measured current (Is) and the internal resistance (Rmt) of the battery (BAT); interrupting (E36) the charge as soon as the determined differential is less than the margin (^) guaranteeing an open-circuit voltage (VOcv) of the battery (BAT) less than the charging voltage (Vmax).

3. Method according to claim 2, wherein the differential between the charging voltage and the open-circuit voltage (VOcv) of the battery (BAT) is determined (E35) by Rint^s with Is the measured current and Rint the internal resistance of the battery.

4. Method according to claim 3, wherein the internal resistance (Rint) of the battery is measured (E22) at the first full charge, the battery being fully charged at the first charge (E2) when the differential between the charging voltage and the open-circuit voltage (Vocv) of the battery is less than the margin (^) protecting the internal resistance of the battery.

5. Method according to claim 3, wherein the internal resistance (Rint) of the battery is measured (E32) before the application of the charging voltage, preferably every 10 to 100 charges.

6. A method according to any one of the preceding claims, wherein the margin (7) is between 10 mV and 250 mV, preferably 100 mV.

7. A method according to any one of the preceding claims, comprising, before charging the battery, a measurement step (E0) of the open-circuit voltage (Vocv) across the battery terminals, charging starting if the measured voltage is below a threshold from which the internal resistance of the battery is no longer protected.

8. A method according to any one of the preceding claims, wherein at the first charge (E2), the method comprises the following steps: a) charging (E21) the battery for a maximum duration (X), preferably between 10 seconds and 100 seconds, typically 60 seconds; b) measuring (E22) the internal resistance of the battery; c) measuring (E23) the open-circuit voltage (VOcv) across the terminals at the end of the determined duration; d) determining (E24) a differential between the charging voltage and the open-circuit voltage (Vmax - VOcv); repeating steps a) to d) as long as the differential between the charging voltage and the open-circuit voltage (Vocv) of the battery is less than the margin (7) protecting the internal resistance of the battery, the method comprising during step a) e) measuring (E25) the current (Is) flowing through the battery (BAT) during charging;f) determination (E26) of the differential between the charging voltage (Vmax) and the open-circuit voltage (VOcv) of the battery (BAT) as a function of the measured current (Is) and the internal resistance of the battery (BAT); g) interruption (E26) of the first charge if the determined differential is less than the margin (7).

9. Battery charging system (1) comprising a processor (1) for implementing a method according to any one of the preceding claims.

10. Product computer program comprising program code instructions for carrying out the steps of the process according to any one of claims 1 to 8, when the program is run on a computer.

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