FR3115933A1 - Power supply system - Google Patents

Abstract

The invention relates to an electrical power supply system (4) comprising an electrochemical module (M) and a safety device suitable for monitoring said electrochemical module (M), said safety device comprising: A heat-sensitive composition (5) comprising one or several temperature-sensitive fillers configured to degrade at a temperature below a threshold temperature, said composition being placed on at least part of the electrochemical module, detection means configured to detect degradation of said thermosensitive composition following an increase temperature above said threshold temperature. Figure to be published with abstract: Figure 3

Description

Power supply system

Technical field of the invention

The present invention relates to an electrical power supply system comprising an electrochemical module and a safety device intended to monitor said electrochemical module.

State of the art

In an electrochemical module, an electrochemical cell is capable of producing electricity by implementing chemical reactions. The chemical energy of the reaction is converted into electrical energy.

An electrochemical module can comprise one or more electrochemical cells arranged in the same casing and connected in series/parallel using metal foils.

Currently, the most commonly used electrochemical cells are of the lithium-ion type. One of them is known in particular under the reference 18650, designating its shape (cylindrical) and its size (18mm in diameter and 65mm in length). Such a cell is for example described in patent US8323825B2 . Recently, 21700 standard cells have also been proposed.

These cells of the 18650, 21700 type or other cylindrical formats comprise a container, called a cup, of cylindrical shape, in which is placed a roller, also called a bobbin, bringing together the two electrodes. An electrolyte is then injected into said well. The cup is closed at its lower end and open at its upper end, a cap being affixed to this upper end to close the container hermetically.

Such a lithium cell is waterproof and generally has protective devices on its cap to prevent it from exploding in cases of abusive use (in temperature or in charge). These protective devices include the following:

• A current interrupt device (CiD – for "Current Interrupt Device" ) which interrupts the current in the event of overpressure in the bucket, without affecting this pressure;
• An overpressure vent generally made in the form of a bursting disc which allows gases to be released, in order to prevent an explosion;
• Finally, the bucket itself can also be weakened in order to open in optimal conditions to prevent an excessively violent explosion;

When several cells are grouped together in the same casing to form a module, it has been shown that the presence of a hot spot at the level of a cell, at the level of the foils or the bus bars, could present a risk not negligible for the integrity of the module. This hot spot may for example come from too high a local impedance, following a faulty or degraded weld. Thus during a high current inrush, it is possible to reach a temperature high enough to generate a thermal runaway of the cell adjacent to that which carries the hot spot. The publication entitled "Electrochemical, Post-Mortem, and ARC Analysis of Li-Ion Cell Safety in Second-Life Applications" shows that, in a lithium-ion battery, from 85°C, a chain of exothermic reactions is initiated, which could lead to thermal runaway of the module.

In the presence of too high a local impedance, it is therefore possible to reach a sufficient temperature (>130°C) in a zone close to the faulty cell to initiate an exothermic reaction chain.

Moreover, although the temperature increase induced by the defect can be very significant, it is relatively difficult to detect it because it is often very local. Thus, a particularly fine thermocouple network would be required to identify the fault.

The object of the invention is to provide an electrical power supply system provided with a safety device which makes it possible, at the level of its module, to detect a local temperature increase, said safety device being in particular reliable and easy to install. .

This object is achieved by an electrical power supply system comprising an electrochemical module and a safety device suitable for monitoring said electrochemical module, said safety device comprising:

• A heat-sensitive composition comprising one or more temperature-sensitive fillers configured to degrade at a temperature below a threshold temperature, said composition being placed on at least part of the electrochemical module,
• Detection means configured to detect degradation of said heat-sensitive composition following a temperature increase beyond said threshold temperature.

According to one feature, the heat-sensitive composition comprises one or more temperature-sensitive fillers chosen from:

• Baking soda,
• Azodicarbonamide,
• Hydrazine,
• Sulfur,
• titanium hydride,
• Zirconium(II) hydride,
• Polyvinylpyrrolidone.

According to another feature, the heat-sensitive composition is made from a solvent chosen from xylene, methoxy-propanol or ethylbenzene or a solvent of the aqueous type.

According to another feature, the heat-sensitive composition comprises a filler based on baking soda and in that the detection means comprise a CO2 sensor.

According to another feature, said detection means comprise at least one sensor chosen from among a gas sensor, a temperature sensor and a pressure sensor.

According to another feature, the detection means comprise means for processing the data collected.

According to a particular embodiment, the detection means comprise a gas sensor and the processing means are configured to compare the data collected by the gas sensor with a gas concentration threshold and/or with a concentration variation threshold of said gas.

According to a particular aspect of the invention, the heat-sensitive composition is placed on a wall of at least one electrochemical cell of the electrochemical module, on an internal wall of the electrochemical module, and/or on one or more electrical connection means of the electrochemical module .

Preferably, the heat-sensitive composition is deposited on a wall of an electrochemical cell of the electrochemical module and said heat-sensitive composition is configured to degrade at a temperature below the thermal runaway temperature of said electrochemical cell.

Preferably, the heat-sensitive composition is in the form of a varnish deposited directly on said at least part of the module or in the form of a label applied to said at least part of the module.

According to a variant embodiment, the heat-sensitive composition may comprise heat-degradable capsules enclosing a volatile solvent.

The invention also relates to a method for manufacturing an electrical power supply system as defined above, this method comprising a step of placing the heat-sensitive composition on said at least part of the electrochemical module.

According to one feature, the arrangement step consists of a step of coating or vaporizing said heat-sensitive composition directly on said at least one part of the electrochemical module, or in a step of applying a film or a label carrier of the heat-sensitive composition.

The invention finally relates to a method for monitoring an electrochemical module of an electrical power supply system as defined above, this method comprising steps of:

• Measurement of a parameter using detection means over time,
• Comparison of the data measured by said detection means with a first threshold value and/or of the variation of the data measured with a second threshold value,
• Generation of an alert signal by the detection means in the event of the first threshold value being exceeded and/or the second threshold value being exceeded.

Brief description of figures

Other characteristics and advantages will appear in the detailed description which follows given with regard to the appended drawings in which:

• FIG. 1 schematically represents an electrochemical cell of cylindrical format and of the lithium-ion type.

• FIGS. 2A and 2B represent an electrochemical module formed from the assembly of several electrochemical cells, respectively in side view and in top view.

• FIG. 3 schematically represents the power supply system according to the invention.

• Figure 4 shows a diagram illustrating the evolution of the CO ₂ concentration as a function of temperature.

Detailed description of at least one embodiment

In the rest of the description, the terms "top", "bottom", "lower", "upper", "above", "below" are to be understood with reference to the vertical axis (X) represented on the .

The safety device of the invention is in particular perfect for monitoring the behavior of an electrochemical module, in particular of one or more electrochemical cells within the electrochemical module of an electrical power supply system 4, but also electrical connections such as foils, busbars employed in the module.

An electrochemical module generally comprises a box (called "casing" in English) housing one or more electrochemical cells. The cells can be juxtaposed in the box and arranged in several rows and columns, for example in staggered rows as illustrated by the and the .

In an M module, cells 1 can be connected to each other in series/parallel by using metal foils 3 ( ).

In a non-limiting manner, each electrochemical cell can be of the lithium-ion type.

In a non-limiting manner and in the appended drawings, each electrochemical cell is represented with a cylindrical format of revolution.

Each electrochemical cell is for example of the 18650 or 21700 type.

It should be understood that the safety device of the power supply system of the invention can be adapted to any part of the module, locally or globally, for example on one or more of its cells, on electrical connections of the module, on the inside wall of its case.

With reference to the , in a non-limiting manner, a conventional lithium secondary cell of the 18650 or 21700 type has a cylindrical shape with a circular base, developed around the axis (X). Such a cell is for example described in patent US8323825B2.

In a non-limiting manner, such a lithium cell 1 mainly comprises a container comprising an upper head comprising an upper wall 100 carrying the positive pole, a lower head comprising a lower wall 101 carrying the negative pole and a side wall 102. The container is generally composed of a bucket 10, of cylindrical shape, and a cap 15 fixed on the bucket and closing the latter on its upper part. This cup 10 defines an internal volume 11 in which are placed the two electrodes 12 (represented by a single set on the ). The two electrodes 12 are made on either side of a flexible insulating plate wound to form a cylindrical assembly which is housed in the cup 10 and forming a bobbin. An electrolyte is then injected into the internal volume 11 of the bucket. A central insert 16 can be inserted axially into the cup 10. The cell has two connection tabs 13, 14 each connected to a separate electrode. On its upper part, the cup 10 is hermetically closed by a cap 15. This cap 15 carries a stack located inside the cup 10 and formed of an overpressure vent 150, a current interrupter device 151 , optionally a PTC type thermistor 152 (with a positive temperature coefficient), and an external cover 153 forming a first electrical connection terminal of the cell.

The current switch device 151 is actuated by the vent 150 when the pressure of the gases present inside the bucket 10 becomes too high. In this situation of excessive pressure, the vent 150 deforms until it breaks the current switch device 151 located above, then causing the interruption of the electric current supplied. If the pressure of the gases present inside the cup continues to increase, the vent 150 may deform until it ruptures, so as to allow the gases to be released to the outside.

The main overpressure vent is generally placed on the side of the positive pole of the cell, on its upper part. Optionally, it can be replaced or supplemented by a vent placed on the side of the negative pole.

As indicated above and illustrated by the and the , an electrochemical module M may comprise a casing 2 containing several identical electrochemical cells 1, for example of cylindrical format, arranged in staggered rows ( ).

The principle of the invention consists in using a safety device responsible for detecting a temperature increase at the level of the module M by employing a thermosensitive chemical composition 5 which comprises one or more fillers sensitive to temperature and configured to degrade at a temperature given, defined as a threshold temperature from which a first alert must be issued. It may for example be a temperature which is lower than the thermal runaway temperature (for example 110° C.) of an electrochemical cell in the case where the composition is deposited on the cell or in its environment of immediate thermal conductivity. But this alert threshold temperature can also be a different temperature if the heat-sensitive composition is deposited on another part of the module, for example on the foils or electric bus bars, in order to help identify possible points hot due to electrical conduction (e.g. welding fault).

The heat-sensitive composition 5 is placed on one or more walls in the internal space of the module M. By way of example and in a non-limiting way, this can be a wall of at least one cell 1 of the module, of all the cells of the module or of certain cells of the module only, an internal wall of the module casing, that of one or more foils or of a bus bar.

The composition can in particular be placed on all or part of the wall of the container of the cell 1. On the , the side wall of the container of each cell is for example coated with the heat-sensitive composition 5 (shown in gray on the ). There shows other examples of location of the heat-sensitive composition in the module, for example on the internal wall of its casing 2, or on metal foils 3 connecting the cells together.

The heat-sensitive composition can also be placed over the entire electrochemical module, for example by immersing the latter in a bath containing said composition. This will in particular make it possible to detect faults in the electrical connection between its cells.

The security device further comprises detection means. These detection means are responsible for detecting the increase in temperature.

The detection means may comprise one or more gas, temperature and/or pressure sensors C housed in the module casing. The solution which consists in using at least one gas sensor housed in the housing 2 of the module M to detect the presence of a gas generated by the degradation of the heat-sensitive composition is particularly advantageous, because it is reliable.

The detection means comprise processing means UC configured to process the data collected by the sensor(s) C.

These processing means can be those already present for the management of the module. These may be the processing means of the BMS (for "Battery Management System"). They can be located outside the M module box.

The C sensor can be placed in the internal space of the module casing, close to cells 1. The same C sensor can be dedicated to several cells. The detection means can also comprise several sensors distributed inside the housing of the module to make the detection more reliable. In this case, the sensors may all be identical. It is also possible to use sensors of different types (gas sensor and temperature sensor for example). The processing means can then be required to correlate the data collected by each of the sensors to better monitor the module. As a variant, the sensor(s) can also be deported in a circuit used by the atmosphere circulating in the module (e.g. closed loop cooling circuit).

The processing means UC can be configured to send an alert signal S1 to alert means 6 in the event of detection of a fault.

The detection means can be configured to detect a threshold overrun of the concentration and/or of the variation of the concentration (measurement of the slope of the curve of variation of the concentration of the gas for example).

The heat-sensitive composition 5 can be in the form of a varnish, a film or a label.

The heat-sensitive composition 5 can also be in the form of capsules enclosing a volatile solvent, said capsule degrading at a given temperature to release said solvent. By way of example, the solvent can be an alcohol or water and the encapsulation could be carried out using a polymer of the polyethylene type or a gelatin. The sensor C will then be suitable for detecting the volatile solvent used (humidity sensor for example).

The heat-sensitive composition 5 can be applied directly to the chosen wall of the module by any known method.

In a non-limiting manner, it may be an application by dipping, by vaporizing a spray or by localized deposition. Any other solution can be considered.

In the form of a film or a label, it can be fixed to the chosen wall, for example by gluing (patch type).

The heat-sensitive composition 5 can be applied before or after assembly of the cells in the module.

In a non-limiting manner, the heat-sensitive composition 5 may for example comprise baking soda (NaHCO ₃ ). Baking soda begins to degrade from 120°C into sodium hydroxide (NaOH) and carbon dioxide (CO ₂ ). Thus, thanks to a CO ₂ sensor C housed in the module casing, it is possible to detect the presence of gas and to alert on the presence of a hot spot.

Of course, it is possible to use compounds other than sodium bicarbonate. In a non-limiting manner, the heat-sensitive composition 5 used can be produced based on one of the following fillers:

• Azodicarbonamide
• Hydrazine
• Sulfur
• titanium hydride
• Zirconium(II) hydride
• Polyvinylpyrrolidone

Depending on the filler used in the heat-sensitive composition 5, the gas released during degradation may be different and the gas sensor used must be adapted to detect the presence of this gas.

For example, with a homogeneous deposit of 1mg/cm² of sodium bicarbonate, a hot spot of 1cm² would produce 2.4E-5 mol of CO2 which represents in a volume of approximately 1 liter, a quantity of 600ppm of CO ₂ , a quantity greater than that of CO ₂ in the air (400ppm). It is understood that it is therefore relatively easy to detect this variation and thus to propose an action aimed at securing the module, for example by cutting off the current demand or the charger of the module in the event of detection of an abnormal quantity of CO ₂ .

Tests on a varnish formulated from sodium carbonate are presented in the graph of the . The test consisted of increasing the temperature in stages of 6°C. On this graph, we see that we can easily correlate an increase in CO2 to an increase in temperature.

As indicated above, the detection means can be configured to detect a threshold overrun of the concentration and/or of the variation of the concentration (measurement of the slope of the curve of variation of the concentration of the gas). For CO2, the concentration threshold can be set for example at around 450ppm and the variation threshold can be set at 10ppm.

Advantageously, in order to avoid risks during the application of the varnish, solvents stable at the potential of the module can be used. By way of example, mention may be made of xylene, methoxy-propanol or ethylbenzene.

As indicated above, the heat-sensitive composition 5 can also be in the form of capsules enclosing, for example, a volatile solvent and degrading at a given temperature.

Example :

An example of mass formulation of a varnish applicable in the form of a spray is as follows:

• Dimethyl ether: 20%
• Sodium carbonate: 20%
• Xylene: 30%
• Cyclohexane: 30%

The manufacturing protocol is for example the following:

• Dissolve the dimethyl ether in the solvents (Xylene and Cyclohexane) using a "disperser" (for example 20 min at 1000 rpm).
• Add the sodium carbonate and disperse for 15 min at 2000 rpm.

The varnish thus formulated can also be used as an electrical insulator.

If it is desired to treat the means of electrical connection (for example of the bus bar type) or the cells before assembly of the module, it is possible to use water as a solvent with more standard binders, of the type polyurethane, acrylic or styrene butadiene. In these compositions, the formulations the dry ratios will then be:

• 60% sodium carbonate
• 40% binder

The dry extract of these formulations will be adjusted according to the application device and may vary between 15 and 35%.

When the heat-sensitive composition 5 is in the form of a film, an aqueous solvent can be used.

Of course, depending on the form of the heat-sensitive composition envisaged, the intended application, the environment of the module, different formulations could be envisaged.

The invention thus has many advantages, including:

• An easy-to-implement solution for detecting the presence of a hot spot within a module;
• A particularly reliable solution. The detection of the presence of gas in particular has an interesting level of reliability.
• A low cost solution thanks to the use of standard compounds and a sensor.

Claims (14)

Power supply system (4) comprising an electrochemical module (M) and a safety device suitable for monitoring said electrochemical module (M), characterized in that said safety device comprises:

• A heat-sensitive composition (5) comprising one or more temperature-sensitive fillers configured to degrade at a temperature below a threshold temperature, said composition being placed on at least part of the electrochemical module,
• Detection means configured to detect degradation of said heat-sensitive composition following a temperature increase beyond said threshold temperature.

System according to Claim 1, characterized in that the heat-sensitive composition (5) comprises one or more temperature-sensitive fillers chosen from:

• Baking soda,
• Azodicarbonamide,
• Hydrazine,
• Sulfur,
• titanium hydride,
• Zirconium(II) hydride,
• Polyvinylpyrrolidone.

System according to Claim 1 or 2, characterized in that the heat-sensitive composition (5) is produced from a solvent chosen from xylene, methoxy-propanol or ethylbenzene or a solvent of the aqueous type. System according to Claim 1, characterized in that the heat-sensitive composition (5) comprises a filler based on sodium bicarbonate and in that the detection means comprise a CO2 sensor (C). System according to one of Claims 1 to 4, characterized in that the said detection means comprise at least one sensor (C) chosen from among a gas sensor, a temperature sensor and a pressure sensor. System according to one of Claims 1 to 5, characterized in that the detection means comprise means (UC) for processing the data collected. System according to Claim 6, characterized in that the detection means comprise a gas sensor (C) and in that the processing means comprise means for comparing the data collected by the gas sensor with a gas concentration threshold and/or with a variation threshold of the concentration of said gas. System according to one of Claims 1 to 7, characterized in that the heat-sensitive composition (5) is placed on a wall of at least one electrochemical cell (1) of the electrochemical module, on an internal wall of the electrochemical module, and/or on one or more electrical connection means of the electrochemical module. System according to Claim 8, characterized in that the heat-sensitive composition (5) is deposited on a wall of an electrochemical cell (1) of the electrochemical module and in that the said heat-sensitive composition (5) is configured to degrade at a temperature below the thermal runaway temperature of said electrochemical cell. System according to one of Claims 1 to 9, characterized in that the heat-sensitive composition (5) is in the form of a varnish deposited directly on the said at least part of the module or in the form of a label applied to said at least part of the module. System according to one of Claims 1 to 9, characterized in that the heat-sensitive composition comprises heat-degradable capsules enclosing a volatile solvent. Method of manufacturing an electrical power supply system as defined in one of Claims 1 to 11, characterized in that it comprises a step of placing the heat-sensitive composition (5) on the said at least part of the module electrochemical (M). Method according to Claim 12, characterized in that the step of disposing consists of a step of coating or of vaporization of the said heat-sensitive composition directly on the said at least part of the electrochemical module, or in a step of applying a film or label bearing the heat-sensitive composition. Method for monitoring an electrochemical module (M) of an electrical power supply system as defined in one of Claims 1 to 11, characterized in that it comprises steps of:

• Measurement of a parameter using detection means over time,
• Comparison of the data measured by said detection means with a first threshold value and/or of the variation of the data measured with a second threshold value,
• Generation of an alert signal (S1) by the detection means in the event of the first threshold value being exceeded and/or the second threshold value being exceeded.