Ultra-fast charging process for an electrochemical accumulator cell

Abstract

The invention relates to a method for charging an electrochemical accumulator cell, in which the voltage across the terminals of the cell is kept constant at at least two successive predefined voltage levels, the charging current supplied to the cell gradually decreasing as the battery charges, the method comprising: E1) a first step of applying a first voltage (V1) across the terminals of the cell, the first voltage (V1) being greater than a usual charging voltage (Vbat), the usual charging voltage (Vbat) being defined as being a voltage such that it would not cause electrochemical degradation of the cell if it were applied over a complete charging cycle of the cell; E2) a second step of applying the usual charging voltage (Vbat). Figure for abstract: Fig. 1

Description

Title of the invention: Method for ultra-rapid charging of an electrochemical accumulator cell Technical field

[0001] The present invention relates to a method for charging an electrochemical accumulator cell, as well as to a system capable of implementing the method.

[0002] An electrochemical storage cell is the basic unit of a battery or electrochemical accumulator. It is composed of two electrodes (an anode and a cathode) and an electrolyte which enables the chemical reactions that generate electrical energy.

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

[0004] The charging speed of a battery depends on many factors, including the capacity of the battery, the battery technology, the charging current, or the safety characteristics.

[0005] There are several state-of-the-art documents aiming to reduce the charging time of a battery.

[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 intended to apply time-varying voltages to the electrodes, comprising, before starting a charging operation for the battery, the steps of: detecting the existence of historical data on previous charging operations of the battery; if detected, processing the historical data to adjust the charging parameters to optimize the charging operation; if not detected, electrically testing the battery to obtain data on the variations in the state of charge (SOC) of the battery, with a view to building a learning model on the SOC variations to be used to optimize the charging operation.

[0007] Document [2] describes a method for fast charging lithium batteries which consists of charging the battery in a first phase by maximizing the charging current, then charging the battery in a second phase by decreasing the charging current in response to an anode potential determined by a reference electrode to maintain the anode potential at or above a threshold, then charging the battery in a third phase by decreasing the charging current in response to the cathodic potential determined by the reference electrode such that the cathodic potential is maximized without exceeding the cathodic potential threshold. A controller can determine an anodic potential or a cathodic potential in real time using a cell potential signal and an anodic cathodic reference electrode signal, respectively. The threshold is the anode potential above which essentially no lithium plating occurs.

[0008] Document [3] describes a rechargeable battery comprising an anode, a cathode, an electrolyte disposed between the anode and the cathode, a protective housing which at least partially surrounds the anode, the cathode and the electrolyte, a heat distributing element disposed at least partially inside the protective housing and configured to receive heat from an external heat source at a desired heating temperature Th in order to heat the battery to a desired temperature Te for charging the battery, thereby reducing the charging time.

[0009] In these prior art documents, the charging time remains very long, several tens of minutes, compared to the application specifications, especially since the energy density tends to increase in new batteries.

[0010] There is therefore a need to provide a method for charging an electrochemical accumulator cell, which significantly reduces the charging time compared to the methods known from the prior art. Summary of the invention

[0011] An object of the invention is therefore a method of charging an electrochemical accumulator cell, in which the voltage across the terminals of the cell is kept constant at at least two successive predefined voltage levels, the charging current supplied to the cell gradually decreasing as the battery charges, the method comprising: El) a first step of applying a first voltage to the terminals of the cell, the first voltage being higher than a usual charging voltage, the usual charging voltage being defined as being a voltage such that it would not cause electrochemical degradation of the cell if it were applied over a complete charging cycle of the cell; E2) a second step of applying the usual charging voltage.

[0012] Advantageously, the first step is applied for a charging parameter such that the internal resistance of the cell is not greater than a predetermined threshold.

[0013] Advantageously, the charging parameter is selected from a charging capacity, a charging current, a charging voltage, or a charging time.

[0014] Advantageously, the first voltage is defined by the formula: Vi=max (2.5*Vbat or 10.5 V) Max corresponding to the maximum voltage, and Vbat corresponding to the usual charging voltage of the cell.

[0015] Advantageously, the percentage of charge capacity generated at the usual charge voltage out of the total capacity generated at the first charge voltage and at the usual charge voltage is between 10% and 50%.

[0016] Advantageously, the cell comprises an electrolyte whose electronic conductivity is less than 109 (Qm) '.

[0017] Advantageously, the cell comprises a solid electrolyte.

[0018] Advantageously, the electrolyte comprises one of the materials selected from LiPoN, Li3OCl, LiSiON, LiN, LATP.

[0019] The invention also relates to a system for managing the charge of a cell, characterized in that it is configured to implement the aforementioned method. Description of the figures

[0020] Other characteristics, details and advantages of the invention will emerge on reading the description given with reference to the appended drawings given by way of example.

[0021] [Fig.l] schematically illustrates the steps of the method according to the invention.

[0022] [Fig.2] illustrates the charge curve of a cell at different charge voltage values, as a function of time.

[0023] [Fig.3] illustrates the energy density supplied as a function of the number of charge / discharge cycles.

[0024] [Fig.4] illustrates the evolution of the internal resistance of the cell as a function of the load.

[0025] [Fig.5] illustrates the internal resistance, for different charging protocols.

[0026] [Fig.6] illustrates a comparison of the method according to the invention with methods known loads from the state of the art.

[0027] The method according to the invention is illustrated by [Fig.l]. In an initial step (not shown), the cell is connected to a suitable power source, which may be a specific charger designed for the chemistry of the cell.

[0028] Optionally, and not shown in [Fig.l], the method may also comprise a step of supplying a fast charging current in order to accelerate charging.

[0029] The method according to the invention comprises an application of a constant voltage across the terminals of the cell, in which the voltage is kept constant at at least two successive predefined voltage levels, the current gradually decreasing as the cell charges.

[0030] The method comprises two steps.

[0031] The first step E1 consists of applying a first voltage Vi to the terminals of the cell, the first voltage Vi being greater than a usual charging voltage Vbat. The usual charging voltage Vbat is defined as being a voltage such that it would not cause electrochemical degradation of the cell if it were applied over a complete charging cycle of the cell.

[0032] The usual charging voltage Vbat, also called "charge cut-off voltage", also corresponds to the voltage at which the cell reaches its maximum capacity at the end of the charging process. It is thus the voltage at which the cell should not be charged beyond this to avoid safety, performance or battery life problems.

[0033] For a battery comprising a plurality of cells, the usual charging voltage is calculated as a function of the total number of cells and the series / parallel arrangement of the cells. The charging voltage of a cell is variable depending on the type of anode and cathode chosen. In the context of the present invention, the usual charging voltage V bat of a lithium-ion cell is 4.2 V.

[0034] The second step E2 consists of applying the usual charging voltage Vbat.

[0035] When the cell is fully charged, the charger can either reduce the current to a very low level (maintenance charge) or stop charging completely (step not shown in [Fig.l]).

[0036] Additionally, once the cell is fully charged, it can be disconnected from the power source to avoid overcharging which could damage the cell (step not shown in [Fig.l]).

[0037] Contrary to what a person skilled in the art might believe, the fact of applying, for a certain quantity of charge relative to the total quantity of charge, a voltage higher than the usual charge voltage, has no harmful influence on the operation of the cell, and makes it possible to drastically reduce the charging time, at constant capacity (from 30 minutes with a conventional charging method to 1 minute 30 with the method according to the invention).

[0038] It is recalled that: Charging time (h) = Battery capacity (Ah) / Charging current (A)

[0039] [Fig.2] illustrates this effect, for a thin-film battery (TFB) 20 pm thick.

[0040] A thin film battery, also called a micro-battery, can be defined as a battery having all of the following characteristics:

[0041] - All active layers (i.e., the positive electrode, the electrolyte and the negative electrode) are made entirely of inorganic material in the solid state. Generally, this means no liquid or gel polymer electrolyte, and no electrode material containing polymer binders as is the case in “standard” batteries are not found in the battery.

[0042] - The individual thickness of all active layers (i.e. the electrode positive, electrolyte and negative layer) electrode) is less than 50 pm In addition, the thickness of the electrolyte is generally less than 5 pm. For standard batteries, the thickness of each layer is generally greater than 100 pm

[0043] - The surface dimensions generally vary from a few mm2 to 10 cm2.

[0044] With a single constant voltage level at the usual charging voltage (Vbat = 4.2 V), a current equal to about 1 mA / cm2 is achieved in a micro-battery. By applying a first voltage V) higher than the usual charging voltage Vbat, a current more than ten times higher can be obtained, without having to extend the charging process. For example, the first voltage Vi can be set to 6 V, 7 V, 8 V, 9 V or 10 V.

[0045] For a cell whose reference voltage is equal to 4.2 V, the first voltage V) can advantageously be defined by the formula:

[0046] Vi=max (2.5*Vbat or 10.5 V)

[0047] Max corresponds to the maximum function.

[0048] [Fig. 3] illustrates a graph of the energy supplied as a function of the number of charge / discharge cycles, in comparison with the method according to the invention (Pi) with a conventional method (Pc) of constant voltage charging, for a TFB battery. The energy remains constant as a function of the number of cycles, whether with only the usual charge voltage (Vbat = 4.2 V), or with a first voltage (Vi = 8 V) then with the usual charge voltage (Vbat = 4.2 V).

[0049] According to an advantageous embodiment, the first step is applied for a quantity of charge such that the internal resistance of the cell is not greater than a predetermined threshold during the first sub-step.

[0050] Indeed, as illustrated in [Fig.4], the internal resistance of the cell tends to remain substantially constant when the constant voltage step comprises only the application of the usual charging voltage (Vbat = 4.2 V), as is the case in the methods known to those skilled in the art. The end of charging causes very little damage to the cell (internal resistance around 10 MΩ / cm2).

[0051] A constant voltage step that would only include the application of a voltage higher than the usual charging voltage (for example 6 V, 8 V or 10 V in [Fig.4]) would cause an increase in the internal resistance of the cell. Depending on the voltage applied, the increase in internal resistance may be slight at the start of charging (zone Z1), then exponential during charging (zone Z2). Thus, it is necessary to avoid the internal resistance being in zone Z2. The method according to the invention is based on the fact that the start of charging can be carried out with a first voltage Vi higher than the usual charging voltage Vbat, so as to remain in zone Zl, then, before the internal resistance exceeds a threshold value, the charging voltage is brought back to the usual charging voltage Vbat.

[0052] One or more intermediate voltages can be used, to avoid abruptly switching from the first voltage Vi to the usual charging voltage Vbat.

[0053] The charging voltage can switch from the first voltage VI to the usual charging voltage Vbat without systematic analysis of the internal resistance. For a type of component, the transition moment can be determined initially using a graph such as that shown in [Fig.4]. The switching point can be determined from a minimum current reached or a charged capacity reached or a measured resistance. Once this point is selected for a configuration, it can be imposed systematically.

[0054] In addition, the internal resistance of the cell can be determined by various methods, including: analyzing the internal voltage drop of the cell when a current is applied, sending a pulsed current to the cell and measuring the voltage response, or impedance analysis by applying an alternating signal to the cell.

[0055] The proportion of charge at the first voltage Vb relative to the total charge quantity (i.e. charge at the first voltage Vi and charge at the maximum charge voltage Vbat) is variable. It can be chosen prior to the start of the charge cycle, as indicated previously, or in real time.

[0056] [Fig.5] illustrates the cycling performance of a cell, with different proportions of the charge at the first voltage Vi compared to the total charge. The cycle life of a cell (or a battery, by extension) refers to its ability to repeatedly and reliably undergo charge and discharge cycles without significant degradation in its performance or capacity.

[0057] As indicated previously, a complete charge at the first voltage Vi (10 V in [Fig.5]), for several charge cycles, would result in a significant increase, from the first charge cycles, in the value of the internal resistance of the cell.

[0058] The application of a first voltage Vi (10 V in [Fig.5]) higher than the usual charging voltage Vbat, then the application of the usual charging voltage Vbat (4.2 V in [Fig.5]), with a percentage of charging capacity generated at the usual charging voltage Vbat on the total capacity generated at the first charging voltage Vi and at the usual charging voltage Vbat between 10% and 50%, makes it possible to contain the degradation of the cell over the charge / discharge cycles. As can be seen in [Fig.5], with values ​​of 14%, 29% and 43%. After about fifty cycles, the internal resistance tends towards a threshold value, respectively of approximately 16 MΩ / cm2, 15 MΩ / cm2 and 14 MΩ / cm2.

[0059] Advantageously, the cell comprises a solid electrolyte, which allows to improve the energy density of the cell. This allows the cell to store more energy for a given size. Solid electrolyte cells are particularly suitable for portable devices such as phones or other connected electronic devices.

[0060] The following table describes the properties of some electrolytes used in solid-state batteries (also called all-solid-state batteries): Electrolyte oei(Qm)1 LPS 109 LTP 109-102 aLZP 109 LAGP 109 - 108 LATP 1010 LGPS — LLZO 108 LLTO 109 LiPON 10 15 - 109 LiSiON 10 13 - 108 Li3OCl 1011 LiN 1012 PEO —

[0061] oei corresponds to the electronic conductivity, in (Qm)1.

[0062] It is clear from the table that LiPON (“Lithium Phosphorus OxyNitride” or lithium phosphorus oxynitride) has a very low electronic conductivity (the electronic conductivity (¾ is between 10 15 and 109 (Qm) *), and can therefore be used as an electrolyte in the charging method according to the invention.

[0063] Electrolytes with an electronic conductivity of less than 109 (Qm)1 have good performance in terms of charging speed. If the electronic conductivity is greater than 109, the electrolyte becomes a less good electrical insulator. Thus, the probability of having electrons in this layer under an electric field is greater, therefore the probability of having the following reaction is higher:

[0064] LC+e^Li

[0065] Such a reaction involves a degradation of the battery performance, because the metallic lithium in LiPON is not mobile like the Li+ ion. It forms dendrites composed of lithium, which lead to a short circuit in the battery.

[0066] Other materials can be used as electrolyte, such as Li3OCl, LiSiON, LiN, LATP (Lithium Aluminum Titanium Phosphate).

[0067] LLZTO (“Lithium Lanthanum Tantalum Zirconia Oxide”) and LLZO (Lithium Lanthanum Zirconate Oxide) have an electronic conductivity which can be higher than 109 (Qm)1; they are therefore incompatible with a fast charging process, as described in [4], [5] or [6].

[0068] [Fig.6] illustrates the performance of the method according to the invention, in comparison with methods of the state of the art.

[0069] The state-of-the-art methods shown in [Fig.6] can be divided into three groups:

[0070] - A first group comprises the methods

[12] and

[13] , which make it possible to obtain a charged capacity between 0.02 and 0.03 mAh / cm2.

[0071] - A second group includes methods [7],

[10] and

[11] , which allow to obtain a charged capacity between 0.2 and 0.3 mAh / cm2.

[0072] - A third group includes methods [8] and [9], which make it possible to obtain a charged capacity between 0.7 and 1 mAh / cm2.

[0073] In the third group, which corresponds to the highest charging capacities among those of the comparative base, the method according to the invention makes it possible to obtain the fastest charging time (100 seconds against 300 seconds for method [8] and 3000 seconds for method [9]).

[0074] The invention also relates to a system for managing the charging of a battery, configured to implement the aforementioned method. As indicated previously, the method has been described for the charging of an electrochemical accumulator cell. It can be extended to the charging of a battery comprising a plurality of cells connected in series and / or in parallel, without this posing any difficulty for those skilled in the art.

[0075] The battery charge management system may in particular control the charge of the battery according to the parameters defined to avoid excessive overcharging, likely to damage the battery. For this, it may comprise a calculation unit which determines in particular the value of the constant current during step E1, the usual charging voltage, the duration of step E1, the value of the first voltage Vb and the duration of step E2.

[0076] References cited

[0077] [1] US 11,677,102 B2

[0078] [2] US 10,446,883 B2

[0079] [3] US 11,444,339 B2

[0080] [4] Yaoyu Ren et al. “Direct observation of lithium dendrites inside gamet-type lithium-ion solid electrolyte”. en. In: Electrochemistry Communications 57 (Aug. 2015), pp. 27-30. DOI: 10.1016 / j.elecom.2015.05.001.

[0081] [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”, en. In: J. Am. Chem. Soc. 136.20 (May 2014), pp. 7395-7402. DOI: 10.1021 / ja502133j.

[0082] [6] Till Fuchs et al. “Current Dépendent Lithium Métal Growth Modes in “AnodeFree” SolidState Batteries at the CuILLZO Interface”, en. In: Advanced Energy Materials 13.1 (Jan. 2023), p. 2203174. DOI: 10.1002 / aenm.202203174.

[0083] [7] N. J. Taylor et al., Journal of Power Sources, vol. 396, pp. 314-318, Aug. 2018.

[0084] [8] K. Niitani et al., ACS Energy Lett., vol. 7, no. 1, pp. 145-149, Jan. 2022.

[0085] [9] T. Kobayashi et al., Electrochimica Acta, vol. 53, no. 15, pp. 5045-5050, Jun. 2008.

[0086]

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

[0087]

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

[0088]

[12] Z. Wang et al., ACS Appl. Mater. Interfaces, vol. 12, no. 43, pp. 48 677-48 683, Oct. 2020.

[0089]

[13] J. Sastre et al., ACS Appl. Mater. Interfaces, vol. 12, no. 32, pp. 36 196-36 207, Aug. 2020.

Claims

Claims

1. A method of charging at least one electrochemical accumulator cell, wherein the voltage across the terminals of the cell is kept constant at at least two successive predefined voltage levels, the charging current supplied to the cell gradually decreasing as the battery charges, characterized in that the method comprises: E1) a first step of applying a first voltage (Vi) across the terminals of the cell, the first voltage (Vi) being greater than a usual charging voltage (Vbat), the usual charging voltage (Vbat) being defined as being a voltage such that it would not cause electrochemical degradation of the cell if it were applied over a complete charging cycle of the cell; E2) a second step of applying the usual charging voltage (V but)*

2. A method according to claim 1, wherein the first step is applied for a charging parameter such that the internal resistance of the cell is not greater than a predetermined threshold.

3. The method of claim 2, wherein the charging parameter is selected from a charging capacity, a charging current, a charging voltage, or a charging time.

4. Method according to one of the preceding claims, in which the first voltage (VJ is defined by the formula: Vi=max (2.5*Vbat or 10.5 V) Max corresponding to the maximum voltage, and Vbat corresponding to the usual charging voltage of the cell.

5. Method according to one of the preceding claims, in which the percentage of charge capacity generated at the usual charge voltage on the total capacity generated at the first charge voltage (VJ and at the usual charge voltage (Vbat) is between 10% and 50%.

6. Method according to one of the preceding claims, in which the cell comprises an electrolyte whose electronic conductivity is less than 109 (Qm) '.

7. A method according to any preceding claim, wherein the cell comprises a solid electrolyte.

8. A method according to one of the preceding claims, wherein the electrolyte comprises one of the materials selected from LiPoN, Li3OCl, LiSiON, LiN, LATP.

9. System for managing the charge of at least one cell, characterized in that it is configured to implement the method according to one of the preceding claims.

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