Thermal Runaway Tests Research Articles

Model-based thermal runaway prediction of lithium-ion batteries from kinetics analysis of cell components

Thermal runaway (TR) is a major safety concern in lithium-ion batteries. Model-based TR prediction is critically needed to optimize safety designs of cells. This paper presents a novel scheme for developing reliable battery TR model from kinetics analysis of cell components. First, differential scanning calorimetry (DSC) tests on the individual cell components and their mixtures are conducted to reveal the TR mechanism and characterize the exothermic reactions, of which the major six (such as the decomposition of solid electrolyte interface (SEI) film) are determined as the dominant heat sources. The kinetics parameters of each exothermic reactions are identified from the DSC tests results at variant heating rates using Kissinger’s method and nonlinear fitting method. A predictive battery TR model is established by superimposing the chemical kinetics equations of the six exothermic reactions. The model fits well with the adiabatic TR test results and the oven tests results of a 24 Ah lithium-ion battery, indicating that the model can well reflect the battery TR mechanism and be trusted to predict battery safety performance without assembling a real battery.

An Overview on Thermal Safety Issues of Lithium-ion Batteries for Electric Vehicle Application

Lithium-ion batteries (LIBs) are being intensively studied and universally used as power sources for electric vehicle applications. Despite the staggering growth in sales of LIBs worldwide, thermal safety issues still turn out to be the most intolerable pain point, and remain the focus of research for technological improvements. This paper presents a comprehensive overview on thermal safety issues of LIBs, in terms of thermal behavior and thermal runaway modeling and tests for battery cells, and safety management strategies for battery packs. Considering heat generation mechanism and thermal characteristics of LIBs, heat generation, dissipation and accumulation inside a cell are elaborated. The triggering factors leading to thermal runaway are also summarized. Finally, thermal runaway detection and prevention strategies for both cell- and pack-levels are introduced. Different engineering approaches from material refinement and additive adoption to thermal, electrical, and mechanical design are presented for thermal runaway prevention.

Determination of the core temperature of a Li-ion cell during thermal runaway

Safety and performance of Li-ion cells is severely affected by thermal runaway where exothermic processes within the cell cause uncontrolled temperature rise, eventually leading to catastrophic failure. Most past experimental papers on thermal runaway only report surface temperature measurement, while the core temperature of the cell remains largely unknown. This paper presents an experimentally validated method based on thermal conduction analysis to determine the core temperature of a Li-ion cell during thermal runaway using surface temperature and chemical kinetics data. Experiments conducted on a thermal test cell show that core temperature computed using this method is in good agreement with independent thermocouple-based measurements in a wide range of experimental conditions. The validated method is used to predict core temperature as a function of time for several previously reported thermal runaway tests. In each case, the predicted peak core temperature is found to be several hundreds of degrees Celsius higher than the measured surface temperature. This shows that surface temperature alone is not sufficient for thermally characterizing the cell during thermal runaway. Besides providing key insights into the fundamental nature of thermal runaway, the ability to determine the core temperature shown here may lead to practical tools for characterizing and mitigating thermal runaway.

Thermal Behaviour of LixMeO2 (Me=Co or Ni+Mn+Co) Cathode Materials

The main challenge for electric vehicles, smaller portable devices and high capacity stationary storage facilities is their safety behaviour under normal and abusive operation conditions. The most commonly used cathodes in lithium-ion batteries (LIB) for portable applications contain lithium cobalt oxide (LiCoO2) as active material. The susceptibility of LiCoO2 cathodes to thermal runaway was previously reported in the framework of safety studies for energy storage systems [1]. The partial substitution of Co by other transition metals was much exploited. One of the main benefits of cells containing electrodes with new chemistries, such as lithium nickel manganese cobalt oxide (Li(NiMnCo)O2, isostructural with the layered LiCoO2), is the improved thermal stability in the fully charged state (delithiated cathodes). LIB with cathodes containing Li(NiMnCo)O2 perform better during thermal runaway tests than those with LiCoO2 [2,3]. Understanding the heat balance between the amounts of heat generated and dissipated in LIB during operation, when the concentration of Li in the electrode varies, is a critical issue. To improve battery safety, thermal management systems (TMS) were introduced to control the operation of high energy and high power batteries. Therefore, knowledge of bulk electrode thermal properties such as thermal conductivity, thermal diffusivity and specific heat capacity are required to optimize TMS design models and for increasing the predictability of multiscale simulations [4]. The thermodynamic properties of LiMeO2 (Me=Ni+Mn+Co) materials for LIB with layered structure were measured by calorimetry up to 973 K. Heat increment and specific heat capacity of samples with Ni:Mn:Co ratio of 1:1:1 and 4:4:2 were determined by transposed drop calorimetry and differential scanning calorimetry. These studies on active materials were extended to cathode level for samples with 1:1:1 stoichiometry. The cathodes under investigation were tape-casted composite thick films, both containing LiMeO2 active material mixed with additives (binder and carbon black), deposited on aluminium current collector foils. To compare the currently studied alternative material (Me=Ni+Mn+Co and Ni:Mn:Co=1:1:1) with the traditional LiCoO2, cathodes with Me=Co were also prepared using the same method and additionally investigated. Due to the presence of the additives, the thermophysical properties of the cathodes were studied as a function of temperature up to 573 K [5]. Thermal diffusivity was measured directly on cathode samples by laser flash analysis, whereas specific heat capacity measurements were performed using differential scanning calorimetry on samples prepared from the composite contained in the cathode sheet. These heat capacity data, together with those for aluminium, were used to predict the cathodes respective heat capacities. Furthermore, the transport properties were also studied as a function of lithium concentration x in the Li x MeO2 cathodes (0≤x≤1). The compositions, which were investigated in this work, were produced by electrochemical titration. The values of x were determined by laser induced breakdown spectroscopy through surface and bulk analysis for homogeneity in lithium concentration [6]. All cathode samples for the laser flash measurements were used in a dry state, without liquid electrolyte in the pores of the composite. Since most of the cell and battery pack models consider a homogeneously distributed mixture of liquid electrolyte in the porous electrodes, data provided in this study could contribute to the improvement of such models through the implementation of dry areas which coexist within cell layers [7]. These areas represent sources of ageing and degradation and lead to thermal gradients across the cells which are up to now neglected in the state of the art of the TMS. The results presented in this work are the first experimental data of this kind which combine application oriented and fundamental research. Furthermore, our temperature and concentration dependent data are critical for significantly improving simulation studies of the thermal behaviour of LIB, including thermal runaway, since current approaches assume bulk properties to be independent of temperature and lithiation degree due to lack of measured data.

Characterization of penetration induced thermal runaway propagation process within a large format lithium ion battery module

This paper investigates the mechanisms of penetration induced thermal runaway (TR) propagation process within a large format lithium ion battery pack. A 6-battery module is built with 47 thermocouples installed at critical positions to record the temperature profiles. The first battery of the module is penetrated to trigger a TR propagation process. The temperature responses, the voltage responses and the heat transfer through different paths are analyzed and discussed to characterize the underlying physical behavior. The temperature responses show that: 1) Compared with the results of TR tests using accelerating rate calorimetry (ARC) with uniform heating, a lower onset temperature and a shorter TR triggering time are observed in a penetration induced TR propagation test due to side heating. 2) The maximum temperature difference within a battery can be as high as 791.8 °C in a penetration induced TR propagation test. The voltage responses have a 5-stage feature, indicating that the TR happens in sequence for the two pouch cells packed inside a battery. The heat transfer analysis shows that: 1) 12% of the total heat released in TR of a battery is enough to trigger the adjacent battery to TR. 2) The heat transferred through the pole connector is only about 1/10 of that through the battery shell. 3) The fire has little influence on the TR propagation, but may cause significant damage on the accessories located above the battery. The results can enhance our understandings of the mechanisms of TR propagation, and provide important guidelines in pack design for large format lithium ion battery.

Thermal characteristics of lithium ion secondary cells in high temperature environments using an accelerating rate calorimeter

The analysis of the thermal behavior of Li-ion secondary cells in high temperature environments is one of the most important issues for the application of these batteries in electric vehicles. In this study, by using an accelerating rate calorimeter (ARC), we monitored the exothermic and thermal runaway behaviors of two lithium ion secondary cells using different cathode materials, lithium cobalt oxide (LCO) and lithium manganese oxide (LMO). Also, the internal resistance and open circuit voltage of the cells were recorded. As a result of the thermal runaway tests, it was found that the amount of heat released from the cell using LMO as the cathode material was lower when compared to the cell using LCO. In general, LMO exhibits a high thermal stability. This is mainly due to differences between the cathode materials. In addition, a sudden increase in the internal resistance and decrease in the open circuit voltage of the cells were detected, which seemed to be due to the shutting down of the cell separators. As already described, by combining the ARC tests and electrochemical measurements, we were able to identify the thermal and electrochemical characteristics, including the thermal runaway, based on the materials used in the Li-ion secondary cells.

Safety of large-capacity lithium-ion battery and evaluation of battery system for telecommunications

In backup power sources for telecommunications equipment, it is desirable that the lithium-ion (Li-ion) cells have large capacity to minimize installation size of backup systems and to improve reliability of them by reducing a number of cells and accompanying protective devices. On the other hand, large-capacity Li-ion cell is difficult to manage safety problems. Therefore, safety improvement must be done to replace lead-acid batteries in conventional backup power sources. Improvement of lifetime has also to be achieved under the float-charging condition.We have been developing large-capacity Li-ion cells of which safety are improved by adding phosphazene flame retardant. In this work, 200-Ahs cell is fabricated and several safety tests under the assumption of telecommunications backup use are carried out. The results show no explosion, ignition, or thermal runaway. Forced thermal runaway test of a cell in the module which involves 13 cells are also carried out. There is no explosion, ignition, or thermal runaway in other 12 cells. In addition, 36-kW Li-ion battery system consisted of the 200-Ahs cells and battery management system (BMS). The system was operated for about 400 days in a state of floating charge. More than 95% of initial capacity is obtained.

Excitation Tests of Prototype HTS Coil With Bi2212 Cables for Development of High Energy Density SMES

Development of the SMES using high temperature superconducting (HTS) coil has progressed as a Japanese national project since FY 2004. The objective of the project is to obtain around twice the normal energy density via an HTS-LTS coil system compared to an LTS coil system. The HTS coil is composed of sixteen double-pancake coils and the double-pancake coil is wound with a Bi2212 Rutherford-type cable. The HTS coil is operated at 4.2 K in liquid helium bath with the LTS coil, and operated at maximum field of 8.9 T. Before we made a hybrid coil system, we verified the design issues using HTS experimental coils. In this paper mechanical compression tests, DC operation tests and thermal runaway tests using the experimental coils are discussed.