Battery test device and method for battery testing

Abstract

Battery test device (10, 10'), with the following features: a centrifuge (20, 20') with a centrifuge arm (22, 22') having a holding device (24, 24a, 24b) for a battery (15) to be tested at one end of the centrifuge arm (22, 22'), wherein the centrifuge (20, 20') is designed to apply a centrifugal force (Fz) to the battery (15) to be tested; a housing (30, 30') inside which the centrifugal alarm (22, 22') is arranged together with the holding device (24, 24a, 24b), wherein the housing (30, 30') is hermetically sealed; wherein the battery test device (10, 10') includes means for evacuating the housing (30, 30') and / or means for generating a vacuum; wherein the battery test device (10, 10') comprises monitoring means for monitoring the battery (15) under test in the form of a gas sensor designed for the detection and composition analysis of a gas emitted by the battery (15).

Description

[0001] Embodiments of the present invention relate to a battery testing device and a method for battery testing. Preferred embodiments relate to a method for simulating the internal short circuit in lithium-ion batteries.

[0002] Due to their relatively high energy density, lithium-ion batteries have become indispensable as energy storage devices, whether in portable devices, electromobility, or stationary energy storage systems. This exceptional prevalence makes safety aspects all the more important. A defective cell can trigger various reactions, from the activation of an internal cell protective function (pressure valve, melting of the separator) to electrolyte leakage and even thermal runaway. Thermal runaway describes the self-reinforcing process of a battery cell heating above a critical threshold, which leads to gas emission and ignition (thermal runaway). Such thermal runaway can be triggered by external or internal influences. External influences include external short circuits, overcharging, and overheating. All of these external causes can be eliminated by implementing appropriate control mechanisms in the system.In contrast, the internal cause, an intrinsic fault, is difficult to detect and therefore cannot be ruled out. In contrast to an external short circuit, with an internal short circuit, the entire current flows through a small area, causing significant heating. In such isolated events, cell surface temperatures of over 600°C have been measured. The emission of hot, toxic gases (Co, HF, etc.) poses a further problem. The risk increases significantly, especially in battery systems with a large number of installed cells, as the probability of a single event is higher in this case and the proximity to other cells can trigger a chain reaction, known as propagation. This causes neighboring cells to ignite. This can lead to catastrophic consequences such as fire or explosion.

[0003] To reduce the risks to a battery system, propagation tests are conducted. The goal of these tests is to demonstrate that, through design measures, the faulty cell does not infect neighboring cells, or that the process is slowed down, and that the fault does not leave the system enclosure. For this purpose, standards require testing of entire battery systems and the use of tests on modules, module segments, and individual cells as preparatory steps. In this process, all conceivable causes of failure are initiated individually. Reproducing the internal short circuit poses a serious challenge.

[0004] Currently, two types of tests are used: mechanical and thermal influences. Mechanical tests include nail and crush tests. These attempt to simulate an internal cell event through an external destructive intervention that short-circuits the layers over a large area and attacks the entire cell surface. This supports heat transfer to the outside (especially in the nail test), promotes gas pressure relief, and enables the escape of the electrolyte. The gas and electrolyte escape points, escape paths, and escape speed are therefore no longer meaningful. Furthermore, the test results are often ambiguous, as they depend heavily on the test conditions. For example, in the nail test, the speed and depth of penetration, the material, geometry, and the finish of the nail surface are decisive. In the crush test, for example, the surface of the cell also plays a role in deformation.

[0005] During thermal destruction tests, the cell is usually heated to a critical temperature by the heating foils (conductive heat conduction). This procedure only partially simulates the real process. For example, after the safety valve is opened, the cell is further heated to force an explosion. In reality, the cell will be electrically isolated at the latest when the valve opens and, depending on the residual chemical activity, has the opportunity to cool down without extreme behavior. Even more importantly, the cell as a whole is preconditioned to the critical temperature (150-200°C depending on the cell type). This supports the chemical chain reaction in the cell and creates a virtually simultaneous, large-scale thermal runaway. In an internal short circuit, on the other hand, the incident initially affects a small area, and the effect gradually spreads to the entire volume.Furthermore, in experiments on modules or module sections, the uniform heating also increases the temperature of neighboring cells, which in turn promotes propagation. In addition to the heating foil, other thermal methods can be found in the literature: laser heating, radiant heating, the use of external thermite reactions, and the integration of microheaters into the electrode.

[0006] A third method that has been frequently discussed in scientific literature in recent years is to conduct the test on a prefabricated cell whose electrode is provided with a copper tab (internal short circuit implant) (see US 8 421 469 B2 and EP 3 316 352 A1). The following disadvantages are obvious with this method: the internal short circuit occurs at the predefined location, the test can only be carried out on new cells, and the manufacturer's involvement is essential. Safe transport presents an additional challenge. Therefore, this procedure is only used in cell research and is correspondingly less widespread. Alternatively, the cell is prepared with a nickel particle. For this purpose, it must be opened, unwound, and rewound under laboratory conditions.

[0007] Battery testing devices exist in the prior art that test batteries using centrifugal acceleration. The document entitled "A Method for Centrifuge Acceleration Testing of Batteries" by Ren Hongqiu is worthy of mention here. Reference is also made to the patent publications and patent applications US 4 553 438 A, WO 2014 / 131 062 A1, US 2002 / 0 086 191 A1, and DE 10 2014 210 656 A1.

[0008] There are already some, partly standardized, approaches to testing batteries and / or accumulators in the state of the art.

[0009] A detailed overview of relevant testing standards and regulations for the automotive sector can be found, for example, in V. Ruiz, A. Pfrang, A. Kriston, N. Omar, P. Van den Bossche, L. Boon-Brett, A review of international abuse testing standards and regulations for lithium ion batteries in electric and hybrid electric vehicles; Renewable and Sustainable Energy Reviews 81 (2018) 1427-1452: 3.1.3 for nail test; 3.1.5 for crush test; 3.2.2.1 and 3.3 for heating test; 3.2.2.2 for nickel particles 3.2.2.3 for implant testing.

[0010] The object of the present invention is to provide a method for battery testing which makes it possible to test batteries without special preparation in such a way that a reliable statement can be made about the quality and / or the age in conjunction with the quality.

[0011] Further features are contained in the independent patent claims.

[0012] The problem is solved by the independent patent claims.

[0013] Embodiments of the present invention provide a battery testing device with a centrifuge. The centrifuge comprises a centrifuge arm having a holding device for a battery to be tested at one end of the centrifuge arm. The centrifuge is configured to apply a centrifugal force to the battery to be tested.

[0014] According to embodiments, the battery testing device may comprise a housing, e.g., in the form of a test bench hood. The housing houses the centrifuge. It should be noted that this housing / hood is optional; e.g., if the tests are conducted in a room designed for this purpose or the test bench is placed in a fire chamber, and the gases emitted by the cell are not to be analyzed, the hood is not required. There are also advantages to controlling the temperature of the test environment for the battery, particularly with regard to efficiency.

[0015] Embodiments of the present invention are therefore based on the finding that applying a centrifugal force to a battery, such as a lithium-ion battery, makes it possible to test the battery, e.g., by first pressing the active material layers in the cell against the cell casing and then pressing them together to cause internal damage. Depending on the quality and age, the runaway of the individual cells will occur at higher or lower angular velocities, ensuring a random location of the internal short circuit. Furthermore, there is no influence between neighboring cells before thermal runaway.

[0016] Another embodiment relates to the use of a centrifuge for testing batteries.

[0017] According to embodiments, the battery test device housing is hermetically sealed, with the centrifugal alarm, for example, being arranged together with the holding device inside the battery test device housing. According to embodiments, the housing is also designed to be fire-resistant. This is intended to prevent the battery from being destroyed inside the housing, while preventing the danger from existing outside the battery test device.

[0018] According to one implementation, the centrifuge may be driven by a motor, e.g., an electric motor, which is arranged, for example, external to the battery testing device housing.

[0019] According to embodiments, means for monitoring the battery to be tested are provided. These monitoring means can, for example, comprise a temperature sensor for measuring the temperature inside the housing of the battery testing device or a temperature sensor for measuring the temperature of the cell to be tested. In general, the temperature sensors can either be attached to the cell to monitor the cell surface temperature or placed somewhere under the hood to measure the ambient temperature and / or the temperature of emitted gases. A pressure sensor (measuring the interior of the battery testing device housing), a gas sensor (to detect any escaping gas), and / or a camera for optically monitoring the battery to be tested can additionally be used as monitoring means. It would also be conceivable for the battery to be electrically contacted in order to perform measurements.

[0020] According to further embodiments, the battery testing device can additionally comprise means for evacuating the battery testing device housing and / or means for generating a negative pressure in the housing and / or for introducing gas (e.g., a noble gas for fire suppression). Furthermore, it would also be conceivable that, according to embodiments, coolants (means for controlling the temperature of the housing interior, e.g., in the battery testing device housing for ambient temperature control) or means for controlling the temperature of the battery to be tested (battery cooling, e.g., via air or coolant) could be arranged on the holding device. Alternatively or additionally, it would also be conceivable to use ignition means (spark ignition) in the housing or in the region of the battery to force a controlled combustion of the emitted gases.

[0021] Regarding the tension arm, it should be noted that, in preferred but not required embodiments, it has a counterweight to prevent imbalance. Regarding the holding device, it should be noted that this is adaptable to the test specimen geometry. For example, it could be interchangeable or an adjustment mechanism could be provided.

[0022] According to embodiments, the centrifuge is designed to apply the centrifugal force according to a braking and / or acceleration profile or according to a braking and / or acceleration profile with at least two maxima or at least two minima of the centrifugal force. Another variant for such a braking and / or acceleration profile would be a stepped profile.

[0023] Another embodiment relates to a method for battery testing. The method comprises the step of applying a centrifugal force to a battery to be tested. The application is carried out using a centrifuge comprising a centrifugal alarm arm, which has a holding device for the battery at one end of the centrifugal alarm arm. Furthermore, the method comprises the further step of observing a destruction situation. According to embodiments, the destruction situation can be detected using monitoring means (e.g., sensors from the group comprising temperature sensors, pressure sensors, gas sensors, or cameras).

[0024] According to one embodiment, the braking and / or acceleration profile mentioned above can be applied to vary the centrifugal force accordingly. This can be achieved, for example, by means of a speed / angular velocity / frequency control. It would also be conceivable to vary ambient conditions, for example, by reducing or increasing the temperature, or by changing the pressure.

[0025] Further developments are defined in the subclaims. Embodiments of the present invention are explained with reference to the accompanying figures. They show: Fig. 1a is a schematic representation of a battery testing device according to a basic embodiment; and Fig. 1b a schematic representation of a battery testing device according to an extended embodiment.

[0026] Before exemplary embodiments of the present invention are explained below with reference to the accompanying drawings, it should be noted that elements and structures with the same function are provided with the same reference numerals, so that the description of them is applicable to one another or interchangeable.

[0027] Fig. 1a shows a battery testing device 10 for testing a battery 15 or generally a unit to be tested with a centrifuge 20.

[0028] The centrifuge 20 can, for example, have a drive means (not shown) and a centrifuge arm 22 with a holding device 24. The holding device 24 serves to hold the battery 15 and is arranged eccentrically to the centrifuge. The centrifuge enables rotation of the arm about the rotation axis 20r, so that an angular velocity φ for the arm 22 can be set for this purpose. As a result, a battery 15 to be tested, arranged in the holding means 24, experiences a centrifugal force Fz. Due to the centrifugal force, the elements of the battery 15 to be tested are mechanically stressed as a result of the centrifugal force Fz.

[0029] For example, during rotation, the active material layers of the cell / battery 15 are deformed. Due to the different elasticity of the layers, the critical approach can occur before the cells are pressed against the cell housing. The cells and the time of the internal short circuit depend only on the homogeneity and quality of the layers. The angular velocity φ or the frequency represents a control parameter that directly influences the exerted force Fz. φ is therefore a control parameter based on which the load on the battery is determined. The load test can be carried out, for example, with increasing φ. With the ageing of the cells and the corresponding formation of dendrites, a faster triggering of thermal runaway is expected. The aim of this load test is, for example, to define and verify the quality limits of batteries.

[0030] Referring to Fig. 1b another embodiment is now explained. Fig. Figure 1b shows a battery testing device 10' with a hermetically sealed, fire-resistant battery testing device housing 30', a centrifuge 20', and a centrifuge arm 22' with two mounts 24a' and 24b'. The centrifuge arm is driven by a drive 26', e.g., an electric motor, which in this embodiment is located outside the housing 30'.

[0031] The battery 15 can be accommodated in the holder 24a', while the holder 24b' accommodates a counterweight 17.

[0032] The method used here can be described as follows. The method is based on the application of centrifugal force. A cell 15 or a module segment is placed on the holder 24a' in the hermetically sealed and fire-resistant battery test device housing 30'. According to optional embodiments, the holder can adapt to the test object geometry. The holders 24a', 24b', or even the holding arm 22 can be quickly exchanged. This is advantageous because it allows for rapid test changes and adaptation to the test object. For example, it would be conceivable for the holders to be designed for all commercially available cells and module segments, either through adjustment options or through various suitable geometries.

[0033] The support arms 24 are driven by an electric motor 26' located outside the enclosed volume 30'. Imbalance can be avoided by using the counterweight 17.

[0034] In the event of a destructive situation (thermal runaway), the housing 30' acts as external protection. According to exemplary embodiments, protective gases such as noble gases can also be used inside the battery test device housing 30', for example, to prevent a fire.

[0035] According to exemplary embodiments, the battery testing device 10' comprises a monitoring device 40, e.g., a camera for video surveillance. This can be provided on the outside of the housing 30' and is designed to observe the interior of the housing 30', or in particular the battery 15, via a transparent area of ​​the housing 30' of the battery testing device 10' (cf. window in the kiln). Additionally or alternatively, monitoring can also be carried out using pressure, temperature, and / or gas sensors (detection and composition analysis). Video surveillance can be carried out, for example, by providing the camera 40 inside or by making part of the housing 30' transparent. Connections for the sensors or cable guides for passing the sensors through the housing 30' can be provided to record the temperature and pressure profiles (not set).

[0036] According to a further embodiment, it would be conceivable for the ambient conditions to be adaptable in terms of the gas provided inside the housing 30' or the pressure or temperature prevailing inside the housing. It would be conceivable for noble gases to be used for fire retardant purposes, and for a corresponding connection to be provided in the housing 30' for this purpose. Evacuation for fire retardant purposes and / or for generating a negative pressure would also be conceivable via this connection. It would also be conceivable for the ambient conditions to be changed by means of coolants or ignition agents.

[0037] Another embodiment relates to the control of the drive 26'. A suitable controller 42' is used to increase or decrease the angular velocity in small steps, thereby allowing a precise determination of the critical value. For this purpose, 42' controls the rotational speed, angular velocity, and / or frequency of the motor 26' or the centrifuge 20'. This has the advantage that statements about the vulnerability (due to manufacturing) and the condition (due to aging) of the cell can be made based on the angular velocity. If necessary, according to further embodiments, braking force can be utilized to amplify the effect, e.g., by rapidly braking the holding arms 22' after thermal runaway or already after the valve opens. Furthermore, rapid braking supports the determination of the measurement parameters.

[0038] For effective observation, monitoring devices can be integrated according to the exemplary embodiments. Temperature, pressure, and gas sensors (detection and composition analysis), as well as video surveillance, are minimum requirements. The use of noble gases for fire suppression must be possible. A corresponding connection should be provided on the device. Furthermore, the device can be expanded with steam or spark-generating (spark igniter) devices or ambient temperature control. Evacuation can be provided as an alternative to noble gases. Speed-coupled video surveillance makes a freeze frame of the test specimen possible. Sensors to be positioned are connected, for example, via bore slip rings. Attaching active cooling to the test specimens is possible. It should be noted that if a test specimen with active cooling is to be tested, a connection (through the hood) to the tempered air or coolant can be provided.

[0039] The combination of precise detection of the angular velocity and the corresponding monitoring or observation of the ambient parameters makes it possible to clearly determine the process time sequences. For example, this can provide information about the process progression of thermal runaway, and a relationship to the distance or change in distance between layers, rotational speed, rotation frequency, or similar can demonstrate the quality of a cell. The process sequence refers to all important process parameters such as irreversibility temperature, transition temperature, maximum temperature, gas ejection velocity, gas ejection direction, etc. According to exemplary embodiments, the gas ejection velocity and direction, which are distorted by rotation, can be computationally corrected.

[0040] The preferred application is the safety testing of lithium-ion batteries, e.g., carried out by cell manufacturers, end-product manufacturers, or certifiers, or in research and development at chemical and cell manufacturers. In general, it can be stated that the proposed test procedure applies at least ten times less energy to the test specimen than the use of heating foils, which corresponds to approximately 1% or less of the energy stored in the cell. Furthermore, there is no material wear, as compared to, for example, the nail test. This method is superior not only for economic reasons, but also from the perspective of mutual influence between neighboring cells before thermal runaway.

[0041] Although some aspects have been described in the context of a device, it should be understood that these aspects also represent a description of the corresponding method, so that a block or component of a device can also be understood as a corresponding method step or as a feature of a method step. Analogously, aspects described in the context of or as a method step also represent a description of a corresponding block, detail, or feature of a corresponding device. Some or all of the method steps may be performed by (or using) a hardware apparatus, such as a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, some or more of the key method steps may be performed by such an apparatus.

[0042] The above-described embodiments are merely illustrative of the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be apparent to others skilled in the art. Therefore, it is intended that the invention be limited only by the scope of the following claims and not by the specific details presented in the description and explanation of the embodiments herein. List of reference symbols 10, 10' battery test device 20, 20' centrifuge 22, 22' centrifuge alarm 24, 24a, 24b Holding device 15 Battery Fz centrifugal force 30, 30' housing 26' engine 40 Monitoring device

Claims

[1] Battery testing device (10, 10'), having the following features: a centrifuge (20, 20') with a centrifuge arm (22, 22') having a holding device (24, 24a, 24b) for a battery (15) to be tested at one end of the centrifuge arm (22, 22'), wherein the centrifuge (20, 20') is designed to apply a centrifugal force (Fz) to the battery (15) to be tested; a housing (30, 30') in the interior of which the centrifugal arm (22, 22') is arranged together with the holding device (24, 24a, 24b), the housing (30, 30') being hermetically sealed; wherein the battery testing device (10, 10') comprises means for evacuating the housing (30, 30') and / or means for generating a negative pressure; wherein the battery testing device (10, 10') comprises monitoring means for monitoring the battery (15) to be tested in the form of a gas sensor which is designed to detect and analyze the composition of a gas emitted by the battery (15). [2] Battery testing device (10, 10') according to claim 1, wherein the centrifuge (20, 20') comprises a motor (26') or electric motor arranged externally to the housing (30, 30') of the battery testing device (10, 10'). [3] Battery testing device (10, 10') according to one of the preceding claims, wherein the battery testing device (10, 10') comprises further monitoring means for monitoring the battery (15) to be tested. [4] Battery testing device (10, 10') according to claim 3, wherein the further monitoring means comprises at least one sensor from the group of the following sensors: a temperature sensor, a pressure sensor and / or a camera. [5] Battery testing device (10, 10') according to one of claims 1-4, wherein the battery testing device (10, 10') comprises means for introducing gas into the housing (30, 30'). [6] Battery testing device (10, 10') according to one of the preceding claims, wherein a counterweight is provided at another end of the centrifugal arm (22, 22'). [7] Battery testing device (10, 10') according to one of the preceding claims, wherein the holding device (24, 24a, 24b) is adjustable. [8] Battery testing device (10, 10') according to one of the preceding claims, wherein the battery testing device comprises ignition means arranged in the housing (30, 30') of the battery testing device (10, 10') and / or on the holding device (24, 24a, 24b), and / or coolants arranged in the housing (30, 30') of the battery testing device (10, 10') and / or on the holding device (24, 24a, 24b). [9] Battery testing device (10, 10') according to one of the preceding claims, wherein the centrifuge (20, 20') is designed to apply the centrifugal force (Fz) according to a braking and / or acceleration profile or according to a braking and / or acceleration profile with at least two maxima of the centrifugal force (Fz). [10] Battery testing device (10, 10') according to one of the preceding claims, comprising a control (42') of the centrifuge (20, 20') or a drive of the centrifuge (20, 20'). [11] Battery testing procedure, comprising the following steps: Applying a centrifugal force (Fz) by means of a centrifuge (20, 20') which is housed in a hermetically sealed housing (30, 30') and comprises a centrifuge arm (22, 22') which has a holding device (24, 24a, 24b) for a battery (15) to be tested at one end of the centrifuge arm (22, 22'); and Evacuating the housing (30, 30') and / or generating a negative pressure in the housing (30, 30'); Observation of a battery destruction situation (15); Monitoring the battery (15) to be tested by means of a gas sensor designed to detect and analyze the composition of a gas emitted by the battery (15). [12] Method according to claim 11, wherein the observation of the destruction situation is carried out by means of monitoring means for monitoring the battery (15) to be tested; or wherein the observation of the destruction situation is carried out by means of monitoring means for monitoring the battery (15) to be tested, wherein the monitoring means comprises at least one further sensor from the group of the following sensors: a temperature sensor, a pressure sensor and / or a camera. [13] Method according to claim 11 or 12, wherein the application of the centrifugal force (Fz) takes place according to a braking and / or acceleration profile or according to a braking and / or acceleration profile with at least two maxima of the centrifugal force (Fz). [14] Method according to claim 11, 12 or 13, with the additional step of externally loading the battery (15) to be tested by means of a temperature reduction, a temperature increase, an ignition, an ambient gas and / or a negative pressure.

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