Method for ultra-fast charging of electrochemical storage cell

Abstract

The invention relates to a method for charging an electrochemical energy storage cell, in which the voltage between the terminals of the cell is kept constant at at least two consecutive predetermined voltage levels, the charging current supplied to the cell is gradually reduced as the cell is charged, the method comprises: a first step of applying a first voltage (V1) to the terminals of the battery cell, the first voltage (V1) being greater than a normal charging voltage (Vbat), the normal charging voltage (Vbat) being defined as a voltage such that if the normal charging voltage is applied over a complete charging cycle of the battery cell, the normal charging voltage does not cause the battery cell to electrochemically degrade; and a second step of applying a normal charging voltage (Vbat) to the charging voltage (E1, E2).

Description

Technical Field

[0001] The present invention relates to a method for charging an electrochemical cell and a system capable of implementing the method. Background Art

[0002] An electrochemically rechargeable battery cell is the basic unit of a battery or an electrochemical accumulator. It consists of two electrodes (an anode and a cathode) and an electrolyte, which enables a chemical reaction for generating electrical energy.

[0003] Depending on the voltage and capacity required for a specific application, the electrochemical battery cells in a battery are connected in series, in parallel, or by a combination of both ways.

[0004] The charging speed of a battery cell depends on many factors, especially the capacity of the battery cell, the technology of the battery cell, the charging current, and the actual safety features.

[0005] There are several documents in the prior art aiming to reduce the charging time of battery cells.

[0006] Document [1] describes an adaptive charging protocol implemented for rapidly charging a rechargeable battery having electrode terminals connected to the terminals of a power supply provided to apply a time-variable voltage to the electrodes. Before starting the charging operation for the battery, the adaptive charging protocol includes the following steps: detecting the presence of historical data regarding a previous charging operation of the battery; if detected, processing the historical data to adjust the charging parameters for the purpose of optimizing the charging operation; if not detected, electrically testing the battery to obtain data regarding the change in the state of charge (SOC) of the battery for the purpose of constructing a training model regarding the SOC change to be used for optimizing the charging operation.

[0007] Document [2] describes a method for rapidly charging a lithium battery, which includes: charging the battery in a first stage while maximizing the charging current; then charging the battery in a second stage while reducing the charging current in response to the anode potential determined by a reference electrode so as to maintain the anode potential at or above a threshold; then charging the battery in a third stage while reducing the charging current in response to the cathode potential determined by a reference electrode such that the cathode potential is maximized without exceeding a cathode potential threshold. The controller can use the battery cell potential signal and the cathode or anode reference electrode signal respectively to determine the anode potential or the cathode potential in real time. The threshold is the anode potential above which lithium plating does not actually occur.

[0008] Document [3] describes a rechargeable battery, which includes an anode, a cathode, an electrolyte disposed between the anode and the cathode, a protective housing at least partially surrounding the anode, the cathode and the electrolyte, and a heat distribution element at least partially disposed inside the protective housing and configured to receive heat from an external heat source at a desired heating temperature Th to heat the battery to a desired temperature Tc for charging the battery. The heat distribution element makes it possible to reduce the charging time.

[0009] In these documents from the prior art, the charging time is still very long relative to the application specifications, reaching dozens of minutes, which increasingly makes the energy density in new batteries tend to increase.

[0010] Therefore, there is a need to provide a method for charging an electrochemical energy storage battery unit, which significantly reduces the charging time compared to the methods known in the prior art. Summary of the Invention

[0011] Therefore, a subject of the present invention is a method for charging an electrochemical energy storage battery unit, in which the voltage between the terminals of the battery unit is kept constant at at least two consecutive predetermined voltage levels, and the charging current supplied to the battery unit gradually decreases as the battery is charged. The method includes:

[0012] E1) A first step of applying a first voltage to the terminals of the battery unit, the first voltage being greater than the normal charging voltage, where the normal charging voltage is defined as such a voltage that if the normal charging voltage is applied during the complete charging cycle of the battery unit, the normal charging voltage will not cause the electrochemical degradation of the battery unit;

[0013] E2) A second step of applying the normal charging voltage.

[0014] Advantageously, the first step is applied to the charging parameters such that the internal resistance of the battery unit does not exceed a predetermined threshold.

[0015] Advantageously, the charging parameters are selected from the charging capacity, the charging current, the charging voltage, and the charging time.

[0016] Advantageously, the first voltage is defined by the following formula:

[0017] V 1 = max(2.5 * V bat or 10.5V),

[0018] where max corresponds to the maximum voltage, and V bat corresponds to the normal charging voltage of the battery unit.

[0019] Advantageously, the charging capacity generated at the normal charging voltage is between 10% and 50% of the total capacity generated at the first charging voltage and at the normal charging voltage.

[0020] Advantageously, the battery cell includes an electrolyte having an electronic conductivity of less than 10 -9 (Ω·m). -1 .

[0021] Advantageously, the battery cell includes a solid electrolyte.

[0022] Advantageously, the electrolyte includes one material selected from the group consisting of LiPoN, Li 3 OCl, LiSiON, LiN, and LATP.

[0023] The present invention also relates to a system for managing the charging of a battery cell, characterized in that the system is configured to implement the above method. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Other features, details, and advantages of the present invention will become apparent upon reading the description given with reference to the accompanying drawings, which are given by way of example.

[0025] Figure 1 Schematically shows the steps of the method according to the present invention.

[0026] Figure 2 Shows the applied voltage and state of charge over time obtained using the method according to the present invention.

[0027] Figure 3 Shows the charging curves of the battery cell at various charging voltage values over time.

[0028] Figure 4 Shows the delivered energy density over the number of charge / discharge cycles.

[0029] Figure 5 Shows the change in the internal resistance of the battery power supply according to the charge.

[0030] Figure 6 Shows the internal resistance for various charging protocols.

[0031] Figure 7 Shows a comparison of the method according to the present invention with charging methods known in the prior art. DETAILED DESCRIPTION

[0032] Figure 1 Shows the method according to the present invention. In an initial step (not shown), the battery cell is connected to a suitable power source, which may be a specific charger designed for the chemistry of the battery cell.

[0033] Optionally, and as not shown in Figure 1 , the method may further include the step of delivering a fast charge current to accelerate charging.

[0034] The method according to the invention comprises applying a constant voltage to the terminals of a battery cell, where the voltage is held constant at at least two successive predetermined voltage levels and the current gradually decreases as the battery cell is charged.

[0035] The method comprises two steps.

[0036] The first step E1 comprises applying a first voltage V 1 to the terminals of the battery cell, the first voltage V 1 being greater than the normal charging voltage V bat . The normal charging voltage V bat is defined as the voltage such that if the normal charging voltage is applied during a complete charging cycle of the battery cell, the normal charging voltage does not cause the battery to deteriorate electrochemically.

[0037] The normal charging voltage V bat (also referred to as the "charge cut-off voltage") also corresponds to the voltage at which the battery cell reaches its maximum capacity at the end of the charging process. Thus, the normal charging voltage is the voltage at which the battery cell must not be further charged in order to avoid problems with safety, performance or battery life.

[0038] For a battery comprising a plurality of battery cells, the normal charging voltage is calculated according to the total number of battery cells and the series / parallel arrangement of the battery cells. Depending on the type of anode and cathode selected, the charging voltage of the battery cell is variable. In the context of the present invention, the normal charging voltage V bat of a lithium-ion battery cell is equal to 4.2 V.

[0039] The method starts in sub-step E10. The state of charge SOC is measured in sub-step E11. If the state of charge is less than the critical state of charge SOC limit (sub-step E12), then the first voltage V 1 is applied (sub-step E13), and then the state of charge SOC is measured (sub-step E14), and so on as long as the state of charge is less than the critical state of charge SOC limit .

[0040] In Figure 2 , the state of charge increases rapidly during the first step E1 (applying the first voltage V 1 ).

[0041] The second step E2 comprises applying the normal charging voltage (Vbat )。

[0042] During Figure 2 this process, during the second step E2, the state of charge increases more slowly and the charging current gradually decreases as the battery is charged.

[0043] When the battery cell is fully charged, the charger can reduce the current to a very low level (charge maintenance) or stop charging completely ( Figure 1 a step not shown in

[0044] During Figure 1 this process, when the state of charge is greater than the critical state of charge SOC limit , a normal charging voltage V bat (sub-step E21)(sub-step E12) is applied. The state of charge SOC is measured (sub-step E22). If the state of charge is greater than the maximum state of charge SOC max (sub-step E23), the method ends (sub-step E24). If not, the normal charging voltage V bat is maintained.

[0045] The maximum state of charge SOC max is defined by the user relative to the characteristics of the battery. The maximum state of charge SOC can be defined and measured in two ways max :

[0046] by the charge capacity (in μAh)

[0047] by measuring the open circuit voltage

[0048] Additionally, when the battery cell has been fully charged, it can be disconnected from the power source to avoid overcharging that may damage the battery cell ( Figure 1 a step not shown in

[0049] Contrary to what those skilled in the art may believe, applying a voltage greater than the normal charging voltage for a specific charge amount relative to the total charge amount has no adverse effect on the operation of the battery cell and makes it possible to greatly reduce the charging time at a constant capacity (from 30 minutes using a conventional charging method to 1 minute and 30 seconds using the method according to the present invention).

[0050] Recall that: charging time (h) = battery capacity (A.h) / charging current (A)

[0051] Figure 3 This effect is shown for a 20-μm thick thin film battery (TFB).

[0052] A thin film battery (also known as a micro battery) can be defined as a battery that exhibits all of the following characteristics:

[0053] All active layers (i.e., the positive electrode, the electrolyte, and the negative electrode) consist only of solid inorganic materials. Generally, this means that there is no liquid or gel polymer electrolyte in the battery and no electrode material containing a polymer binder, as is the case in a "standard" battery.

[0054] The individual thickness of all active layers (i.e., the positive electrode, the electrolyte, and the negative electrode layers) is less than 50 μm. Additionally, the thickness of the electrolyte is generally less than 5 μm. For a standard battery, the thickness of each layer is usually greater than 100 μm.

[0055] The dimensions of the surface area typically vary from several mm 2 to 10 cm 2 and vary.

[0056] In the case of a single constant voltage level (V bat = 4.2 V) at the normal charging voltage, a current equal to approximately 1 mA / cm 2 is achieved in the microbattery. By applying a first voltage V bat greater than the normal charging voltage V 1 , a current greater than ten times can be obtained without having to extend the charging process. For example, the first voltage V 1 can be fixed at 6 V, 7 V, 8 V, 9 V, or 10 V.

[0057] For a battery cell with a reference voltage equal to 4.2 V, the first voltage V 1 can be advantageously defined by the following formula:

[0058] V 1 = max(2.5 * V bat or 10.5 V).

[0059] max corresponds to the maximum function.

[0060] Figure 4 A graph showing the energy delivered according to the number of charge / discharge cycles compares the method according to the invention (Pi) with a conventional constant voltage charging method (Pc) for TFB. Depending on the number of cycles, the energy remains constant, only in that the normal charging voltage (V bat = 4.2 V) is used, or the first voltage (V 1 = 8 V) is used and then the normal charging voltage (V bat = 4.2 V) is used.

[0061] According to an advantageous embodiment, a first step is applied for a charge quantity such that the internal resistance of the battery cell during the first sub-step does not exceed a predetermined threshold.

[0062] In fact, as Figure 5As shown, when the constant voltage step includes only applying the normal charging voltage (V bat = 4.2V), the internal resistance of the battery cell has a tendency to remain substantially constant, as is the case in methods known to those skilled in the art. The end of charging causes very little degradation in the battery cell (about 10 MΩ / cm 2 of internal resistance).

[0063] A constant voltage step that includes only applying a voltage greater than the normal charging voltage (e.g., Figure 5 6V, 8V, or 10V in Figure 5 bat will cause an increase in the internal resistance of the battery cell. Depending on the applied voltage, the increase in internal resistance at the start of charging (region Z1) may be slight and then increase exponentially during charging (region Z2). Therefore, the internal resistance must be prevented from being in region Z2. The method according to the invention is based on the fact that charging can start at a first voltage V 1 greater than the normal charging voltage V bat in order to remain in region Z1 and then, before the internal resistance exceeds a threshold value, bring the charging voltage back to the normal charging voltage V

[0064] One or more intermediate voltages can be used in order to avoid a sudden transition from the first voltage V 1 to the normal charging voltage V bat

[0065] The charging voltage can be switched from the first voltage V 1 to the normal charging voltage V bat without a systematic analysis of the internal resistance. For a type of component, the transition moment can be determined in the first phase using a graph such as that depicted in Figure 5 The switching point can be determined based on the minimum current reached or the charged capacity reached or the measured resistance. When this point has been selected for a configuration, it can be applied systematically.

[0066] In addition, the internal resistance of the battery cell can be determined by various methods, in particular: analyzing the internal voltage drop of the battery cell when a current is applied, sending a pulsed current to the battery cell and measuring the voltage response, or actually analyzing the impedance by applying an AC signal to the battery cell.

[0067] The proportion of the charge at the first voltage V 1 relative to the total charge (i.e., the charge at the first voltage V 1 and the charge at the maximum charging voltage V bat ) is variable. This proportion can be selected before the start of the charging cycle, as described above, or in real time.

[0068] Figure 6 shows the cycling behavior of a battery cell, where the various ratios of the charge at a first voltage V 1 to the total charge. The cycling strength of a battery cell (or, in general, a battery) refers to the capacity of the battery cell to repeatedly and reliably undergo charge and discharge cycles without significantly degrading its performance or its capacity.

[0069] As described above, for a number of charging cycles, fully charging at a first voltage V 1 ( Figure 6 10 V in

[0070] will result in: an increase in the internal resistance value of the battery cell starting from the first charging cycle. bat Apply a first voltage V 1 ( Figure 6 10 V in bat ( Figure 6 4.2 V in bat greater than the normal charging voltage V 1 and then apply the normal charging voltage V bat such that the percentage of the charging capacity generated at the normal charging voltage V Figure 6 to the total capacity generated at the first charging voltage V 2 and at the normal charging voltage V 2 is between 10% and 50%, making it possible to constrain the degradation of the battery cell during charge / discharge cycles, as 2 visible in

[0071] where the values are 14%, 29% and 43%. After about 50 cycles, the internal resistance tends towards threshold values of approximately 16 MΩ / cm

[0072] The following table describes the properties of certain electrolytes for solid electrolyte batteries (also known as all-solid-state batteries):

[0073] Electrolyte <![CDATA[σ el (ohm.m) -1 > LPS <![CDATA[10 -9 > LTP <![CDATA[10 -9 -10 -2 > αLZP <![CDATA[10 -9 > LAGP <![CDATA[10 -9 -10 -8 > LATP <![CDATA[10 -10 > LGPS - LLZO <![CDATA[10 -8 > LLTO <![CDATA[10 -9 > LiPON <![CDATA[10 -15 -10 -9 > LiSiON <![CDATA[10 -13 -10 -8 > <![CDATA[Li 3 OCl]]> <![CDATA[10 -11 > LiN <![CDATA[10 -12 > PEO -

[0074] σ el corresponds to the electronic conductivity, in units of (Ω.m) -1 .

[0075] It is evident from the table that LiPON (lithium phosphorus oxynitride) has a very low electronic conductivity (electronic conductivity σ el between 10 -15 and 10-9 (Ω·m) -1 and can thus be used as an electrolyte in the charging method according to the present invention.

[0076] whose electronic conductivity is less than 10 -9 (Ω·m) -1 exhibits good performance in terms of charging speed. If the electronic conductivity is greater than 10 -9 , the electrolyte becomes a less good electrical insulator. Therefore, the probability of electrons existing in the layer under an electric field is high, and thus the probability of the following reaction is high:

[0077] Li + + e− → Li

[0078] This reaction involves the deterioration of battery performance because the lithium metal in LiPON is not as mobile as Li + ions. It forms dendrites composed of lithium, which leads to a short circuit in the battery.

[0079] Other materials can be used as electrolytes, such as Li 3 OCl, LiSiON, LiN, and LATP (lithium aluminum titanium phosphate).

[0080] LLZTO (lithium lanthanum tantalum zirconium oxide) and LLZO (lithium lanthanum zirconate oxide) have an electronic conductivity that may be greater than 10 -9 (Ω·m) -1 ; thus they are incompatible with fast charging methods, as described in [4], [5], and [6].

[0081] Figure 7 shows the performance of the method according to the present invention compared to the methods of the prior art.

[0082] Figure 7 The methods from the prior art depicted in

[42] can be divided into three groups:

[0083] The first group includes methods

[12] and

[13] , which make it possible to obtain a charged capacity between 0.02 and 0.03 mAh / cm 2 ;

[0084] The second group includes methods [7],

[10] , and

[11] , which make it possible to obtain a charging capacity between 0.2 and 0.3 mAh / cm 2 ;

[0085] The third group includes methods [8] and [9], which make it possible to obtain a charged capacity between 0.7 and 1 mAh / cm 2 ;

[0086] In the third group, which corresponds to the highest charging capacity among the charging capacities from the comparison basis, the method according to the invention makes it possible to obtain the fastest charging time (100 seconds, as opposed to 300 seconds for method [8] and 3000 seconds for method [9]).

[0087] The invention also relates to a system for managing the charging of a battery, which system is configured to implement the above method. As described above, a method for charging an electrochemical energy storage battery cell has been described. It can be extended to charging a battery comprising a plurality of battery cells connected in series and / or in parallel, which presents no difficulty for a person skilled in the art.

[0088] The system for managing the charging of a battery can in particular control the charging of the battery according to the defined parameters in order to avoid overcharging which can easily damage the battery. To this end, the system can comprise a calculation unit which in particular determines the value of the constant current during step E1, the normal charging voltage, the duration of step E1, the value of the first voltage V 1 and the duration of step E2.

[0089] Cited references

[0090] [1] US11,677,102B2.

[0091] [2] US10,446,883B2.

[0092] [3] US11,444,339B2.

[0093] [4] Yaoyu Ren et al. “Direct observation of lithium dendrites inside garnet-type lithium-ion solid electrolyte”. In: Electrochemistry Communications 57 (Aug. 2015), pp. 27 - 30. DOI: 10.1016 / j.elecom.2015.05.001.

[0094] [5] Rachna Khurana et al. “Suppression of Lithium Dendrite Growth Using Cross-Linked Polyethylene / Poly(ethylene oxide) Electrolytes: A New Approach for Practical Lithium-Metal Polymer Batteries”. In: J. Am. Chem. Soc. 136.20 (May 2014), pp. 7395 - 7402. DOI: 10.1021 / ja502133j.

[0095] [6] Till Fuchs et al. “Current-Dependent Lithium Metal Growth Modes in "Anode-Free" Solid-State Batteries at the Cu|LLZO Interface”. In: Advanced Energy Materials 13.1 (Jan. 2023), p. 2203174. DOI: 10.1002 / aenm.202203174.

[0096] [7] N.J. Taylor et al., Journal of Power Sources, vol. 396, pp. 314 - 318, Aug. 2018.

[0097] [8] K. Niitani et al., ACS Energy Lett., vol. 7, no. 1, pp. 145 - 149, Jan. 2022.

[0098] [9] T. Kobayashi et al., Electrochimica Acta, vol. 53, no. 15, pp. 5045 - 5050, Jun. 2008.

[0099]

[10] G.-L. Zhu et al., Energy Storage Materials, vol. 31, pp. 267 - 273, Oct. 2020.

[0100]

[11] H. Yamauchi et al., Sci Rep, vol. 10, no. 1, p. 9453, Jun. 2020.

[0101]

[12] Z. Wang et al., ACS Appl. Mater. Interfaces, vol. 12, no. 43, pp. 48677 - 48683, Oct. 2020.

[0102]

[13] J. Sastre et al., ACS Appl. Mater. Interfaces, vol. 12, no. 32, pp. 36196 - 36207, Aug. 2020.

Claims

1. A method for charging at least one electrochemical storage cell, wherein: The voltage between the terminals of the battery cell is kept constant at at least two consecutive predetermined voltage levels, and the charging current delivered to the battery cell is gradually reduced as the battery is charged, Characterized in that the method comprises: E1) a first step of applying a first voltage (V1) to the terminals of the battery cell, the first voltage (V1) being greater than a normal charging voltage (V bat ), the normal charging voltage (V bat ) is defined as a voltage such that if the normal charging voltage is applied during a complete charging cycle of the battery cell, the normal charging voltage does not cause the battery cell to electrochemically degrade; E2) applies the normal charging voltage (V bat )’s second step.

2. The method according to claim 1, wherein: The first step is applied with respect to charging parameters so that the internal resistance of the battery cell is not higher than a predetermined threshold.

3. The method according to claim 2, wherein: The charging parameter is selected from among charging capacity, charging current, charging voltage and charging time.

4. The method according to claim 1, wherein: The first voltage (V1) is defined by the following formula: V1=max(2.5*V bat or 10.5V), max corresponds to the maximum voltage, and V bat Corresponding to the normal charging voltage of the battery cell.

5. The method according to one of the preceding claims, wherein: The charge capacity generated by the normal charge voltage is relative to the charge capacity generated by the first charge voltage (V1) and the normal charge voltage (V bat )The percentage of total capacity generated is between 10% and 50%.

6. The method according to one of the preceding claims, wherein: The battery cell includes an electrolyte having an electronic conductivity of less than 10 -9 (Ω.m) -1 .

7. The method according to one of the preceding claims, wherein: The battery cell includes a solid electrolyte.

8. The method according to one of the preceding claims, wherein: The electrolyte includes one material selected from among LiPoN, Li3OCl, LiSiON, LiN, and LATP.

9. The method according to one of the preceding claims, wherein: As long as the state of charge of the electrochemical storage cell is less than a predefined critical value (SOC limit ), applying the first voltage (V1).

10. The method according to one of the preceding claims, wherein: As long as the state of charge of the electrochemical storage cell is less than a predefined maximum value (SOC max ), the normal charging voltage (V bat ).

11. A system for managing the charging of at least one battery cell, characterized in that The system is configured to implement the method according to one of the preceding claims.

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