System and method for quantitatively measuring the gases generated by a battery cell or battery cell component as a function of time during testing

Abstract

A method for measuring gases generated by at least a portion of a battery cell comprises placing a test sample in a chamber. The test sample comprises either a battery cell with terminals and a gas port or a test fixture with terminals and a gas port that receives at least a portion of a battery cell. The method comprises connecting the gas port of the test sample to a node; supplying a carrier gas at a known pressure and flow rate to the node; taking gas samples at or downstream of the node using a mass spectrometer and / or a gas analyzer; and determining the concentrations of gases in the test sample using the at least one mass spectrometer and / or the gas analyzer.

Description

INITIATIONThe information provided in this section is intended to generally illustrate the context of the disclosure. Work of the present inventors, insofar as described in this section, as well as aspects of the description that may not be prior art at the time of filing, is neither expressly nor silently recognized as prior art over the present disclosure.The present disclosure relates to battery cells, and more particularly to systems and methods for qualitatively measuring battery cell gases during operation and / or heating of the battery cells.Electric vehicles (EVs), such as battery-powered electric vehicles (BEVs), hybrid vehicles, and / or fuel cell vehicles, include one or more electric machine(s), and a battery system having one or more battery cells, modules, and / or packs. A power control system is used to control the charging and / or discharging operation of the battery system during charging and / or driving.The battery cells include a housing enclosing a battery cell stack with one or more cathode electrodes, anode electrodes, separators, and electrolyte. The cathode electrodes include a cathode active material layer disposed on a cathode current collector. The anode electrodes include an anode active material layer disposed on an anode current collector.When the battery cell is exposed to certain conditions, such as formation change, overcharge, or elevated temperature, reactions that generate gases occur within the battery cell. Since the battery cell stack is disposed in a sealed case, it is difficult to determine the type of gases generated, the gas concentrations, and / or the time of gas generation.SUMMARYA method for measuring gases generated by at least a portion of a battery cell includes disposing a test pattern in a chamber. The test pattern includes either a battery cell having terminals and a gas terminal or a test device having terminals and a gas terminal that receives at least a portion of a battery cell. The method comprises connecting the gas port of the test sample to a node; supplying a carrier gas at a known pressure and flow rate to the node; sampling gas at or downstream of the node using a mass spectrometer and / or a gas analyzer; and determining concentrations of gases in the test sample using the mass spectrometer and / or the gas analyzer.In other features, a check valve includes a first port connected to the battery cell and a second port connected to the node. The carrier gas is supplied at a first flow rate that is greater than or equal to ten times a second flow rate of gases generated from the sample during testing.The carrier gas comprises a mixture of an inert gas and a reference gas having a predetermined concentration.In other features, the mass spectrometer and / or the gas analyzer comprise the mass spectrometer. The mass spectrometer is calibrated with the reference gas as an internal standard. The test specimen is heated to a predetermined temperature during the test. The test sample is heated during the test on the basis of a temperature profile as a function of time.In other features, the method includes charging the test pattern to a predetermined voltage prior to testing. The method comprises supplying current to and / or extracting current from the test pattern during the test. The method includes sensing a voltage of the battery cell as a function of time during the test.In other features, the method includes connecting the mass spectrometer to the node using a capillary. The method includes purging the chamber with a purge gas during testing. The method includes monitoring chamber temperature, battery cell temperature, battery cell pressure, and / or chamber pressure as a function of time during the test.A system for measuring gases in a battery cell includes a chamber having a cavity configured to receive a test pattern, the test pattern including either a battery cell having terminals and a gas terminal or a test device having terminals and a gas terminal and receiving at least a portion of a battery cell. A check valve includes a first port connected to the gas port of the battery cell and a second port connected to a node. A first gas source supplies the junction with a carrier gas comprising an inert gas and a reference gas having a predetermined concentration. A mass spectrometer and / or a gas analyzer are configured to sample gas at the junction and determine a concentration of one or more gases in the battery cell as a function of time using the mass spectrometer.In other features, the carrier gas is supplied at a first flow rate that is greater than or equal to ten times a second flow rate of gases generated from the test sample during testing. The mass spectrometer and / or the gas analyzer comprises the mass spectrometer. The mass spectrometer is calibrated with the reference gas as an internal standard.In other features, a heating element heats the test pattern to a predetermined temperature during testing or heats the test pattern based on a temperature profile as a function of time during testing.In other features, a voltage / current sensor / current source is configured to charge the test pattern to a predetermined voltage prior to testing, supply current to and draw current from the test pattern during testing, and / or monitor current and / or voltage of the test pattern as a function of time during testing.In other features, the system includes a chamber pressure sensor to monitor pressure in the chamber as a function of time during testing and / or a test pattern pressure sensor to monitor pressure in a housing of the battery cell or in the test device.Further areas of applicability of the present disclosure will become apparent from the detailed description, claims and drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.BRIEF DESCRIPTION OF THE DRAWINGSThe present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: FIG. 1A is a side cross-sectional view of an example of a battery cell having a battery cell stack with A anode electrodes, C cathode electrodes, and S separators disposed in a battery case according to the present disclosure; FIG. 1B is a side cross-sectional view of a test device having at least a portion of a battery cell according to the present disclosure; FIGS. 2A and 2B are functional block diagrams and schematics of an example of a gas test system for a battery cell according to the present disclosure; FIG. 3 is a flow diagram of an example of a method of operating the gas test system of FIGS. 2A and 2B, in accordance with the present disclosure; FIG. 4 is a graph illustrating an example of the target temperature and the battery cell temperature versus time according to the present disclosure; and FIG. 5 is a graph depicting an example of gas concentration percentages, voltage, and cell temperature versus time according to the present disclosure.In the drawings, reference numerals may be reused to identify similar and / or identical elements.DETAILED DESCRIPTIONAlthough battery cell inspection according to the present disclosure is described in connection with battery cells for vehicles, the battery cells may also be used in other applications, e.g., stationary applications.The present disclosure relates to a gas test system and method configured to quantitatively measure gas generated in a test pattern that includes either a battery cell or a test device having at least a portion of a battery cell. The test pattern may be tested in real time while the operating parameters are controlled to predetermined operating conditions (e.g., corresponding to heating, forming, and / or changing).For example, the test pattern may be heated to a predetermined temperature based on a time-varying temperature profile or may not be heated during the test. The gases generated by the sample are entrained in a carrier gas. In some examples, the carrier gas comprises an inert gas and a reference gas having a known or predetermined concentration. The gases of the test sample and of the reference gas are measured with a mass spectrometer and / or a gas analyzer. For example, during the test, the mass spectrometer measures one or more gases quantitatively as a function of time, the reference gas concentration serving as a reference.In some examples, the battery cell includes a battery cell stack enclosed in a flexible battery housing, such as a pouch cell. In other examples, the battery cell includes a battery cell stack enclosed in a prismatic, cylindrical, coin-shaped, or other hard metal battery housing with heat resistant gaskets. In still other examples, one or more sets of cathode electrodes, anode electrodes, and / or separators are disposed in the test fixture, including a gas port, ports, and a device for applying pressure to the one or more sets of cathode electrodes, anode electrodes, and / or separators. In further examples, individual components or combinations of components of a battery cell, such as anode electrode, cathode electrode, separator, and / or electrolyte, may be housed in the test device / housing. The components may be preconditioned, e.g., by changing or charging, then disassembled and reassembled in the test fixture.In some examples, the mass spectrometer draws the samples of the carrier gas and the battery cell gases at a location downstream of the test pattern using a mass spectrometer sampling line such as a capillary. The gas mixture with the carrier gas is supplied at a constant flow rate and constant pressure so that the pressure and flow remain almost constant when the gas is generated by the test sample. The precise dosing of the reference gas (in the carrier gas) allows the mass spectrometer to quantify other gases that are taken from the sample, such as hydrogen, carbon dioxide, ethylene, ethane, methane or other gases.The battery test system allows quantitative measurement of calibrated gases in real time, direct comparison from one test to another, and avoidance of electrolyte contamination of the mass spectrometer. For example, gas from the battery cell may be measured in situ during heating, forming, switching, and / or other operating conditions that generate gas within the battery cell. Although any battery cell format with a gas port may be used, hard case battery cells (or test devices) allow exhaust gas analysis at higher battery cell temperatures and pressures.Referring now to FIG. 1A, a battery cell 10 includes C cathode electrodes 20, A anode electrodes 40, and S separators 32 arranged in a predetermined order in a battery cell stack 12, where C, S, and A are integers greater than zero. The battery cell stack 12 is disposed in a case 50. The C cathode electrodes 20- 1, 20- 2,..., and 20- C include cathode active material layers 24 disposed on one or both sides of a cathode current collector 26.The A anode electrodes 40- 1, 40- 2,..., and 40- A include anode active material layers 42 disposed on one or both sides of the anode current collectors 46. In some examples, the A anode electrodes 40 and the C cathode electrodes 20 exchange lithium ions during charging / discharging, although other chemistry may also be used. In some examples, one or both of the cathode active material layers 24 and / or the anode active material layers 42 comprise dry coatings comprising one or more active materials, one or more optional conductive additive(s), and / or one or more optional binder material(s) applied (e.g., cast, laminated, applied, etc.) to the current collectors.In some examples, the cathode current collector 26 and / or the anode current collector 46 include metal foil, metal mesh, perforated metal, three-dimensional metal foam (3D metal foam), and / or expanded metal. In some examples, the current collectors are made of one or more materials selected from the group consisting of copper, stainless steel, brass, bronze, zinc, aluminum, and / or alloys thereof.The outer tabs 28 and 48 are respectively connected to the current collectors of the C cathode electrodes 20 and the A anode electrodes 40, and may be disposed on the same or different sides of the battery cell stack 12. The outer tabs 28 and 48 are connected to the terminals 60 and 62 of the battery cells. In some examples, the housing 50 includes a gas port 64.In FIG. 1B, a test apparatus 80 includes a cover 82 and a bottom portion 84, optional terminals 88 and 90 for providing connections to a portion 91 of a battery cell, and a gas terminal 92 for withdrawing gases during the test. In some examples, the portion 91 of the battery cell is disposed in the bottom portion 84, and the cover 82 optionally applies pressure to the portion 91 of the battery cell (or another pressurizing device is used).Referring now to FIGS. 2A and 2B, a gas test system 100 for a battery cell includes a chamber 110 having a cavity 113 enclosed by a lid 111. In FIG. 2A, a heating element 114 may be used to control the temperature of the chamber 110 and the test pattern 120. A chamber temperature sensor 134 measures the temperature of the chamber 110.A test pattern temperature sensor 138 measures a temperature of the test pattern 120 (e.g., a battery cell or a test device comprising at least a portion of a battery cell). As can be appreciated, the heating element 114 may be controlled in response to feedback from the chamber temperature sensor 134 and / or the test pattern temperature sensor 138.The test pattern 120 is disposed in a cavity of the chamber 110. The test pattern 120 includes a gas terminal 124, and optionally positive and negative terminals 122. In some examples, the gas port 124 may be connected by a gas line to a port 128, e.g., a quick connect coupling.A voltage and current sensor / current source 132 (e.g., a potentiostat) is connected to the positive and negative terminals 122. The voltage and current sensor / current source 132 measures the voltage at the positive and negative terminals 122 of the test pattern 120 (if used). The voltage and current sensor / current source 132 may also apply and / or vary voltage and current across the positive and negative terminals 122 of the test pattern 120 as a function of time (or an event or operating parameter) during the test.In some examples, a purge gas source 150 provides purge gas (e.g., an inert gas such as argon (Ar)) via a pressure regulator 151, a flow regulator 152, and a shut-off valve 154 to purge chamber 110. A shut-off valve 190 is connected to chamber 110 to provide chamber venting for venting the purge gases. A chamber pressure sensor 158 measures the pressure within the chamber 110.In some examples, a check valve 178 is disposed between the test pattern 120 and a node 179. In some examples, the check valve 178 opens when a pressure difference between a battery cell side and a drain side of the check valve 178 is greater than a predetermined pressure difference. In some examples, the predetermined pressure difference is less than or equal to 1 psi (e.g., 1 / 3 psi).A gas source 170 supplies carrier gas. In some examples, the carrier gas comprises a predetermined mixture of an inert gas and a reference gas connected to node 179 via pressure regulator 172 and flow regulator 174. Node 179 is also connected to a sampling line 186 (e.g., a capillary) connected to a vent, a mass spectrometer 188, and an optional gas analyzer 184. In some examples, the gas analyzer 184 includes a Fourier Transform Infrared Spectroscopy (FTIR) gas analyzer, a gas chromatography (GC) gas analyzer, a gas sensor such as a hydrogen sensor, and / or a volatile organic compound (VOC) sensor. As can be appreciated, gas sampling may be performed by the mass spectrometer 188 and / or by one or more of the gas analyzers 184.The mass spectrometer 188 takes samples of the carrier gas (e.g., including the inert gas and reference gas at a known concentration) from the gas source 170 and the gas generated by the test sample (e.g., the battery cell or a portion of a battery cell). The mass spectrometer measures the gas concentrations in the known reference gas and in the gases from the battery cell. Examples of extracted gases include molecular hydrogen (H 2), carbon dioxide (CO 2), methane (CH 4), ethane (C 2 H 6), ethylene (C 2 H 4), molecular oxygen (O 2), carbon monoxide (CO), helium (He), argon (Ar), etc. In some examples, the reference gas includes any gas that does not belong to any of the battery cell gases to be examined by mass spectrometer 188. The reference gas may comprise helium (He), for example. The inert gas may include, for example, argon (Ar).In Figure 2B, the gas streams during the test are shown. The gas source 170 provides the known gas mixture at a controlled pressure and flow rate. The reference gas is supplied in the known gas mixture at a predetermined concentration. In some examples, the known gas mixture has a flow rate that is greater than the flow rate of the gases generated by the battery cell. In some examples, the flow rate of the known gas mixture is at least ten times greater than the flow rate of the gases generated by the battery cell. For uniformity reasons, the flow rate of the carrier gas is maintained constant from one battery cell test to another to allow comparison.The gas from the battery cell is entrained by the known gas mixture. The flow rate of the known gas mixture is significantly greater than the flow rate of the gas from the battery cell. The mass spectrometer 188 uses a vacuum to draw a small amount of the known gas mixture and gas from the battery cell. The purge gas source 150 may be used to source gases from within the chamber 110.The volumetric flow rate of each calibrated gas is calculated using a volumetric gas flow rate (cc / min)=concentration (%)*flow rate of the carrier gas (cc / min). The volumetric flow rate may be integrated to calculate the total volume of each gas generated at a particular time interval.Referring now to FIG. 3, a method for testing a battery cell is shown. At 208, the battery cell is optionally preconditioned and / or a voltage of the battery cell is adjusted to a predetermined voltage. At 210, the chamber is optionally flushed. At 212, the gas mixture comprising an inert gas and a reference gas having a known concentration is supplied.At 214, the method determines whether the test has begun. If 214 is true, the method optionally monitors the voltage of the battery cell. At 222, the gas is optionally removed from the battery cell using a mass spectrometer and / or a gas analyzer. At 230, the battery is optionally heated to a predetermined temperature, heated based on a temperature profile, and / or charged or discharged using a predetermined charge / discharge profile. At 234, the concentrations of the gases from the battery cell are determined using the mass spectrometer and / or the gas analyzer as a function of time. At 238, the method determines whether the test is complete. If false, the method returns to 218.Referring now to FIGS. 4 and 5, examples of heating and gas concentration data collected during testing of a battery cell are shown. FIG. 4 shows a temperature profile of the battery cell during the test. The temperature is increased by the heating element based on a target temperature Ts during the test. The temperature of the battery cell T then rises.In FIG. 5, the battery cell is first charged to a predetermined voltage V. When the temperature T of the battery cell rises, the separator melts and causes a short circuit, whereby the voltage drops to almost zero. Times and concentrations of various gases (e.g., CO 2, CH 4, C 2 H 4 and H 2) are acquired in real time. For example, as the temperature rises, the CO 2- concentration increases significantly. The H 2- concentration also increases.The gas test system for a battery cell according to the present disclosure quantitatively measures the gases generated by the battery cell. The gas test system uses a battery cell having a gas port through which gas flows from the battery cell as the pressure in the battery cell increases. The battery cell may be a pouch battery cell or a hard shell battery cell.The voltage and current sensor / current source (e.g., a potentiostat) monitors the cell voltage and / or charges / discharges the battery cell. The optional check valve prevents the return flow of carrier gas into the battery cell and prevents the electrolyte from drying out. The optional pressure sensor measures the pressure of the gas that exits the gas connection of the battery cell.Upon heating, the heating element heats the chamber and the battery cell. In some examples, the chamber is flushed with an inert gas (e.g., Ar) to entrainment gases / particles in the event of thermal runaway. Testing of hardshell battery cells and gas port is possible to a predetermined temperature (e.g., -3000° C.). A temperature sensor, e.g., a thermocouple, measures cell temperature.The foregoing description is for illustrative purposes only and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure may be embodied in a variety of forms. While this disclosure includes particular examples, the true scope of the disclosure should not be so limited as other modifications will become apparent upon examination of the drawings, the specification, and the following claims. It should be appreciated that one or more steps within a method may be performed in different orders (or concurrently) without changing the principles of the present disclosure. Although each of the embodiments described above has particular features, one or more of these features described with respect to any embodiment of the disclosure may be implemented in any other embodiment and / or combined with features of any other embodiment, even if this combination is not expressly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described with various terms including "connected," "engaged," "coupled," "adjacent," "next to," "top on," "over," "under," and "arranged.". When a relationship between first and second elements is not expressly described as "direct" in the above disclosure, this relationship may be a direct relationship in which no other intervening elements are present between the first and second elements, but may also be an indirect relationship in which one or more intervening elements (either spatially or functionally) is / are present between the first and second elements. As used herein, the phrase "A, B, and / or C" should be construed using a non-exclusive logical OR operation as a logical (A ORed with B ORed with C) rather than as "at least one of A, at least one of B, and at least one of C.".In the figures, the direction of an arrow as indicated by the arrow head generally indicates the flow of information (e.g., data or instructions) of interest for the display. For example, if element A and element B exchange a variety of information, but the information conveyed from element A to element B is relevant to the mapping, the arrow may point from element A to element B. This unidirectional arrow does not mean that no other information is transmitted from element B to element A. In the case of information sent from element A to element B, element B may further send requests for the information to element A or confirm the receipt thereof.LegendIn the drawing figures, N represents No and Y represents Yes.

Claims

A method of measuring gases generated by at least a portion of a battery cell, comprising: disposing a test pattern in a chamber, the test pattern comprising one of: a battery cell having terminals and a gas terminal; and a test fixture having terminals and a gas terminal that receives at least a portion of a battery cell; connecting the gas terminal of the test pattern to a node; supplying a carrier gas of known pressure and flow rate to the node; sampling gas at or downstream of the node using a mass spectrometer and / or a gas analyzer; and determining the concentrations of gases in the test pattern using the mass spectrometer and / or the gas analyzer.The method of claim 1, further comprising a check valve having a first port connected to the battery cell and a second port connected to the node.The method of claim 1, wherein the carrier gas is supplied at a first flow rate that is greater than or equal to ten times a second flow rate of gases generated by the test pattern during the test.The method of claim 1, wherein the carrier gas comprises a mixture of an inert gas and a reference gas having a predetermined concentration.The method of claim 4, wherein: the mass spectrometer and / or the gas analyzer comprises the mass spectrometer, and the mass spectrometer is calibrated with the reference gas as an internal standard.The method of claim 1, wherein the test pattern is heated to a predetermined temperature during the test.The method of claim 1, wherein the test pattern is heated during the test based on a temperature profile as a function of time.The method of claim 1, further comprising charging the test pattern to a predetermined voltage prior to testing.The method of claim 1, further comprising supplying power to the test pattern during testing and / or drawing power from the test pattern during testing.The method of claim 1, further comprising sensing a voltage of the battery cell as a function of time during the test.

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