Safety Of Li-ion Batteries Research Articles

Comparison of Model-Based and Sensor-Based Detection of Thermal Runaway in Li-Ion Battery Modules for Automotive Application

In recent years, research on lithium–ion (Li-ion) battery safety and fault detection has become an important topic, providing a broad range of methods for evaluating the cell state based on voltage and temperature measurements. However, other measurement quantities and close-to-application test setups have only been sparsely considered, and there has been no comparison in between methods. In this work, the feasibility of a multi-sensor setup for the detection of Thermal Runaway failure of automotive-size Li-ion battery modules have been investigated in comparison to a model-based approach. For experimental validation, Thermal Runaway tests were conducted in a close-to-application configuration of module and battery case—triggered by external heating with two different heating rates. By two repetitions of each experiment, a high accordance of characteristics and results has been achieved and the signal feasibility for fault detection has been discussed. The model-based method, that had previously been published, recognised the thermal fault in the fastest way—significantly prior to the required 5 min pre-warning time. This requirement was also achieved with smoke and gas sensors in most test runs. Additional criteria for evaluating detection approaches besides detection time have been discussed to provide a good starting point for choosing a suitable approach that is dependent on application defined requirements, e.g., acceptable complexity.

Polyether sulfone and Li6.4La3Zr1.4Ta0.6O12 based polymer-in-ceramic electrolyte with enhanced conductivity at low temperature for solid state lithium batteries

Developing solid state lithium batteries (SSLBs) is an essential step to overcome current safety and energy density issues of traditional Li-ion batteries. As the core component of SSLBs, a solid electrolyte with high ionic conductivity, great physical and chemical properties is still under exploration. Herein, a novel “polymer in ceramic” composite polymer-ceramic electrolytes (CPEs) is reported, which is composed of a polyether sulfone (PESF) polymer and cubic Li6.4La3Zr1.4Ta0.6O12 (LLZTO) ceramic with high contents (up to 80 wt. %). The as-prepared PESF-LLZTO CPEs possess good heat resistance and high mechanical strength to maintain structural integrity. The optimized 0.2PESF-0.8LLZTO CPEs exhibits an excellent ionic conductivity of 4.13×10−4 S cm−1 with a tLi+value as high as 0.64 at 20 °C after wetted by trace wetting agent (6.0 ul cm−2). More impressively, the ionic conductivity is still reached 1.49×10−4 S cm−1 at -10 °C and 9.42×10−4 S cm−1 at 80oC. Meanwhile, the 0.2PESF-0.8LLZTO CPEs shows a broad electrochemical window (≤4.8 V vs. Li+/Li) and an excellent compatibility with Li metal. Density functional theory calculations and 6Li solid-state NMR characterizations suggest that strong interactions among LLZTO, PESF and wetting agents contribute to the enhanced conductivity. As a proof for practical application, the Li||0.2PESF-0.8LLZTO CPEs||LiFePO4 full cells deliver a specific discharge capacity of 133.2 mAh g−1 at 2.0 C, and successfully run over 80 cycles at 0.5 C without capacity attenuation at 20 °C. The full cell also demonstrates a possibility for the application at low temperature down to -10oC and high temperature up to 60oC. This work brings a new perspective for high-performance SSLBs.

A highly ionic conductive succinonitrile-based composite solid electrolyte for lithium metal batteries

Solid-state Li metal batteries with solid electrolytes have built a potential way to solve the safety and low energy density problems of current commercial Li-ion batteries with liquid electrolyte. As a key component of solid-state Li metal batteries, solid electrolytes require high ionic conductivities and good mechanical properties. We have designed a composite solid electrolyte (CSE) consisting of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)-Li6.5La3Zr1.5Ta0.5O12 (LLZTO)-succinonitrile (SN) and Li bis(trifluoromethylsulphonyl)imide (LiTFSI). The PVDF-HFP-based porous matrix made by electrospinning ensures good mechanical properties of the electrolyte membrane, and the large proportion of SN filling material makes the electrolyte membrane have an ionic conductivity of 1.11 mS·cm−1 without the addition of liquid electrolyte. The symmetric battery assembled with CSE can be cycled stably for more than 600 h, and the LiFePO4∣CSE∣Li full battery can also be cycled stably for more than 200 cycles. In addition to Li metal batteries, Li-O2 and Li-CO2 batteries that use CSE as electrolytes also have good performances, reflecting the universality of CSE. CSE does not only guarantee good mechanical properties but also obtain a high ionic conductivity. This design provides a new idea for the commercial application of polymer-based solid batteries.

Toward High-Voltage Solid-State Li-Metal Batteries with Double-Layer Polymer Electrolytes

Solid polymer electrolyte batteries with a Li-metal anode and high-voltage active materials hold promising prospects to increase the energy density and improve the safety of conventional Li-ion batteries. An adequate choice of the polymers used for the cathode (catholyte) and for the separator (electrolyte) to create a sufficient energy gap and improve the chemical compatibility at both the positive electrode and Li-metal anode is required. The present work highlights the advantages of the double-layer polymer electrolyte approach in cells with a LiNixMnyCozO2 active material, a poly(propylene carbonate) (PPC) catholyte, and a poly(ethylene oxide) (PEO) electrolyte. Replacing PEO in the catholyte with PPC results in a remarkably improved cycling performance. In addition, the higher lithium transference number of electrolytes with single lithium ion conductors leads to a smooth cycling of solid-state batteries. Cells with 1 mAh cm–2 deliver 160 mAh g–1, with a capacity retention above 80% over 80 cycles and a Coulombic efficiency close to 100%.

Modeling the effect of electrolyte microstructure on conductivity and solid-state Li-ion battery performance

Solid-state batteries offer the potential to improve safety, cyclability, and energy density of Li-ion batteries. However, their conductivity, stability, and processing limit their use. To this end, the effects of solid electrolyte microstructure on overall battery performance are determined. The conductivities of Al-doped Li7La3Zr2O12 (Al-LLZO), with a range of microstructures, are found using a resistor network model. Varying electrolyte properties are combined with a Li-metal negative electrode and LiCoO2 positive electrode in a 1-D continuum model to predict the effects on performance. Simulations suggest that the ratio of electrolyte conductivity to electrolyte thickness must remain above 10 S m−2 to maintain high energy and power output, particularly at C-rates greater than 10. To maintain conductivity near the grain interior conductivity, a grain size at least 10,000 times larger than grain boundary thickness is needed. Further improvements in grain size, grain boundary thickness, and void fraction beyond typical Al-LLZO microstructures, with the goal of higher conductivities, are predicted to have diminishing returns in overall battery performance, even at more sensitive high C-rates up to 100.

Performance comparison between straight channel cold plate and inclined channel cold plate for thermal management of a prismatic LiFePO4 battery

An efficient battery thermal management system is indispensable for ensuring the safety and stability of Li-ion batteries. In this work, for applications of a prismatic LiFePO4 battery in electric vehicle, an inclined channel cold plate is designed based on the straight channel cold plate. The performance of the straight channel cold plate and the inclined channel cold plate are numerically investigated and compared under different coolants, channel numbers and mass flow rates. The j/f factor considering the fluid flow and heat transfer characteristics is employed to judge the comprehensive performances of cold plates. Results show that the performance of inclined channel cold plate is much better than that of straight channel cold plate. The j/f factor of the straight channel cold plate is improved by 79.64% when the coolant is water, the mass flow rate is 0.6 g s−1, the channel number is 5 and the inclined angle is 15°. Furthermore, effects of inclined angle are investigated. It is found that the larger the inclined angle the better the performance of the inclined channel cold plate. This work suggests that the inclined channel cold plate is more suitable for applying in the battery thermal management system.

Combining Deformation, Heat, and Ionic Conductivity to Improve the Electrochemical Performance and Safety of Li-Ion Batteries under Extreme Conditions

Combining Deformation, Heat, and Ionic Conductivity to Improve the Electrochemical Performance and Safety of Li-Ion Batteries under Extreme Conditions

Thermodynamics analysis and performance enhancement of battery thermal management system with suitable variations in operating parameters

Electric Vehicles (EVs) will be a major mode of road transportation in short period of time. Batteries are the major source of energy storage for propulsion of EVs in which Li-ion batteries are currently the most suitable option. A suitable temperature range of 15-400C must be maintained for optimal performance and safety of Li-ion batteries, which can be achieve through battery thermal management system. In this study, a PCM based thermal management system has been drafted by considering the heat dissipation rate for 1C, 2C and 3C discharge rate of Li-ion batteries and simulated in ANSYS FLUENT 19.2 software. Suitable alternatives are suggested for the efficient performance of battery thermal management and the effects are also discussed. The result shows that PCM based system was able to hold the battery temperature below 400C with 1C, 2C and 3C discharge rate for time interval of more than 3600 seconds. PCM based system with thickness 10mm shows better result when compared with 6mm and 8mm while the couple PCM based system performs better than PCM with capsule system.

Physical properties and compatibility with graphite and lithium metal anodes of non-flammable deep eutectic solvent as a safe electrolyte for high temperature Li-ion batteries

In this study we present the original formulation of a deep eutectic mixture based on lithium imide salt as an electrolyte for Li-ion batteries. The non-flammable liquid mixture obtained by mixing asymmetric lithium (fluorosulfonyl) (trifluoromethanesulfonyl) imide (LiFTFSI) with ethylene carbonate (EC) demonstrates its applicability as a safer electrolyte for Li-ion batteries. By comparison with conventional electrolytes containing the same salt, in 3EC/7EMC and EC/PC/3DMC, the volumetric properties of (EC-LiTFSI, 3/1, w), abbreviated EC-LiTFSI31, reveal the strong nature of the FTFSI−—EC coordination and the non-solvation of Li+, explaining the "stacking" effect observed. Transport properties (viscosity, conductivity and ionicity) are discussed and compared to those of conventional electrolytes, demonstrating that eutectic EC-LiTFSI31 has the typical ionicity of organized media such as ionic liquids or DESs, even if its concentration in salt is similar to that of the conventional electrolyte of 1 mol L−1.The electrochemical evaluation of the compatibility of this original electrolyte with lithium metal and with graphite in Li//Li and Gr//Li half-cells shows that EC-LiTFSI31 does not cause any erratic or asymmetric polarization over time in lithium metal and that it demonstrates very good intercalation and stability during the charge/discharge of graphite. The thermal and electrochemical stability of EC-LiTFSI31 gives a good performance and an outstanding stability of Gr//Li cell cycling at C/20 or C/10 up to 80 °C, during 5 months (100 cycles) without any damage to the battery. This original formulation could prove to be a promising electrolyte for Li-ion battery safety, which remains the main concern of industrialists in the field.

Free carbonate-based molecules in the electrolyte leading to severe safety concerns of Ni-rich Li-ion batteries.

The safety of Li-ion batteries is one of the most important factors, if not the most, determining their practical applications. We have found that free carbonate-based solvent molecules in the hybrid electrolyte system can cause severe safety concerns. Mixing ionic liquids with a carbonate-based solvent as the co-solvent at a fixed salt concentration of 1 M LiPF6 can lead to free carbonate-based molecules causing poor charge storage performance and safety concerns.

Anchoring Porous F-Tio2 Particles by Directed-Assembly on Pmia Separators for Enhancing Safety and Electrochemical Performances of Li-Ion Batteries

Anchoring Porous F-Tio2 Particles by Directed-Assembly on Pmia Separators for Enhancing Safety and Electrochemical Performances of Li-Ion Batteries

Stable Long Cycling of Small Molecular Organic Acid Electrode Materials Enabled by Nonflammable Eutectic Electrolyte.

Small molecule organic acids as electrode materials possess the advantages of high theoretical capacity, low cost, and good processability. However, these electrode materials suffer from poor cycling stability due to the inevitable dissolution of organic molecules in the electrolytes. Here, a eutectic mixture of lithium bis(trifluoromethanesulfonyl)imide and N-methylamine is employed as a eutectic electrolyte in Li-ion batteries with small molecule organic acids as electrodes. To enhance the cycling stability of the electrolyte, fluoroethylene carbonate is used as an additive. The electrolyte exhibits nonflammability, high ionic conductivity, and good electrochemical stability. Molecular dynamics simulations and density functional theory are performed to further investigate the solvation chemistry of the eutectic electrolyte. The well-designed eutectic electrolyte inhibits the dissolution of terephthalic acid effectively and displays superior performance with a capacity retention of ≈84% after 2000 cycles at a high current density of 1 A g-1 . It also enables stable cycling of more than 900 cycles at a high current density of 2 A g-1 at 60°C. This study provides a strategy to enhance the cycling stability and safety of Li-ion batteries with organic electrode materials.

Modelling of battery thermal management: A new concept of cooling using fuel

Battery thermal management system (BTMS) design is crucial for its performance, which can be associated with extra costs and system complexity. Most of the current studies are focused on the BTMS design but with a little focus on the improvement of coolants. In this work, the feasibility of using combustion engine fuel for the LIB thermal management of hybrid electric vehicles is investigated. N-heptane is used as a dielectric hydrocarbon coolant in the introduced system. The thermal performance of the proposed system is investigated numerically using the CFD software ANSYS-Fluent. To benchmark and validate the system performance, a comparative study is made among other common approaches, including the use of air and 3M-Novec 7200. A variety of input parameters are accounted for, including inlet velocities and discharge rates. The results show that air cooling is the least effective method to control the battery module temperature uniformity and the Li-ion battery safety limit. At the same time, n-heptane and 3M-Novec 7200 have shown good control of the module temperature range (20 °C–40 °C) at various discharge rates and different inlet velocities. However, using n-heptane is a considerable improvement to the cost of the system and reduction in its weight and maximum temperature, compared to that using 3M-Novec 7200 coolant. For instance, at 0.1 m·s-1, n-heptane has reduced the Li-ion battery maximum temperature at 1C and 2C discharge rates by more than 7.9 °C (2.6%) and 17.9 °C (5.65%), respectively, compared to those predicted using the same battery module without cooling.

A numerical analysis on multi-stage Tesla valve based cold plate for cooling of pouch type Li-ion batteries

The operating temperature can significantly influence the performance, cycle life, and safety of Li-ion batteries used in electric vehicles. One of the critical factors is to assess the temperature distribution within the battery pack when operated under extreme conditions and choosing an appropriate cooling method. Concerning this, a liquid cooling plate comprising Tesla valve configuration with high recognition in microfluidic applications is proposed to provide a safer temperature range for pouch type Li-ion batteries. A multi-stage Tesla valve with forward and reverse flow configuration is designed and analysed to improve a conventional rectangular channel's intrinsic temperature gradient issues for turbulent flow conditions. Moreover, the influence of various parameters such as channel number, the distance between two consecutive valves, coolant temperature, and heat flux applied on the cold plate's top and bottom surfaces are numerically investigated for varying Reynold's number using COMSOL Multiphysics software. An enhancement in heat transfer with the reverse flow in multi-stage Tesla valve is seen, mainly caused by flow bifurcation and mixing mechanisms, at the cost of pressure drop. A cold plate with 4 channels and valve to valve distance of 8.82 mm exhibits the most effective cooling performance.

Numerical study of scale effects on self-heating ignition of lithium-ion batteries stored in boxes, shelves and racks

Abstract The fire safety of Lithium-ion batteries (LIBs) during their storage and transport is becoming of prime importance for the industry, with a number of such fires reported in recent years. It is crucial to understand the mechanisms and causes of these fires to provide insights for prevention. Previous studies mostly focused on small ensembles with a few cells and the chemistry involved. The possibility of ignition resulting from heat transfer within a large-size ensemble of LIBs had received little attention before. Focusing on the fire safety of large-scale stored LIBs, we discuss the risk and likelihood of self-heating ignition, which is a known cause of fires in other industries (e.g. chemical storage). Taking LiCoO2 type of battery as a base case and using its chemical kinetics reported in the literature, we build a transient heat transfer model with multi-step reactions to analyze the self-heating behaviour of ensembles of LIBs. Four typical storage sizes, from a single cell to racks containing around 2 million cells, are simulated using COMSOL Multiphysics. The results show that the critical ambient temperature for self-heating ignition is significantly lower for a large-scale LIB ensemble (e.g. 60 °C for the rack), indicating spontaneous side reactions are not negligible heat sources in large LIB ensembles and self-heating poses potential fire hazards in storage. Effects of size and heat transfer in LIB ignition should therefore not be ignored. This work provides insights into the fire safety of Li-ion batteries and additional means of protection during storage and transport.

Monte Carlo assisted sensitivity analysis of a Li-ion battery with a phase change material

Safety of Li ion batteries is as important, if not more, as its performance because its usage in contemporary transport applications can otherwise lead to catastrophic scenarios. Owing to the exothermic reactions and complex heat transfer within the Li ion batteries, they are prone to overheating and possible thermal runaway in the absence of adequate thermal management systems. Therefore, to ensure a safe operation it is key to evaluate the uncertainties with respect to a thermal management system along with the uncertainties in the intricate multiphysical phenomena within the system. To achieve this, we conduct Monte Carlo simulations followed by sensitivity analysis to correlate the variability of 14 different factors with the safety of an 18650 Sony cell with a phase change material (PCM) at stressed conditions. These varied factors correspond to the properties of the 18650 battery and the PCM. From the PCM properties, we identify the temperature at which the PCM starts melting to have most influence on the safety of the battery. In addition, we also estimate the probability of the sub-optimal unsafe scenarios occurring by examining the distribution of the maximum temperature within the battery. Finally, we obtain reduced surrogate models with an accuracy of 92% through supervised machine learning algorithms.

Understanding the Non-Collision Related Battery Safety Risks in Electric Vehicles a Case Study in Electric Vehicle Recalls and the LG Chem Battery

Electric vehicles (EV) are considered the future of the automobile industry due to their high energy conversion efficiency and environmental friendliness. However, there are safety risks associated with Li-ion batteries, including the potential for fires and explosions. This paper reviews the challenges facing the electric vehicle market regarding the implementation of Li-ion batteries. It then presents two case studies of electric vehicles that experienced safety-related recalls which were not associated with vehicle collisions. For comparison, a history of Li-ion battery safety issues from the same brand in other applications than EV and the company's reactions are provided. The case study and review of issues in other applications show a lack of consideration for customer safety, amplified by the additional risk used in an EV. The paper then explores corrective actions performed and analyzes how the actions will not address the root cause; additionally, contributing to a performance reduction. Recommended corrective actions for future implementation of EV batteries are provided.

Superionic Si-Substituted Lithium Argyrodite Sulfide Electrolyte Li6+xSb1–xSixS5I for All-Solid-State Batteries

Lithium-based solid electrolytes have been investigated in many studies for improving the energy density and safety of conventional Li-ion batteries. Recently, Li argyrodites (Li6+xSb1–xSixS5I) hav...

Cycle Life Assessment of Commercial Cells with Ni-Rich Cathode and Si-Graphite Anode: Are Advanced Batteries for Real?

Growing interest in off-grid homes and long-range electric vehicles (EVs) powered by efficient energy storage systems is pushing the boundaries and driving the search for new materials for next-generation of Li-ion batteries (LIBs). For the state-of-the-art LIBs, pack level gravimetric and volumetric densities are smaller than the density values at materials level by up to four and two times, respectively, which makes the battery packs bulky [1, 2]. The next-gen LIB packs are required to be lightweight and extremely compact in order to maximize the usable space for the end-user [3].Since, storage capacity of a battery is a function of its nominal capacity and operating voltage, impetus is on developing LIBs with higher upper cut-off voltages. One method is by replacing traditional cathodes with active materials that exhibit higher redox potentials vs. lithium reference electrode (Li+/Li) e.g. Li-rich layered oxides [4]. Silicon (Si) is a popular choice for high-energy LIB anodes. It is a naturally abundant mineral with the highest known theoretical capacity (4200 mAhg−1) and a low operating potential (< 0.5 V vs. Li/Li+). However, pure Si anodes display poor cyclability mainly due to volume changes in order of 100-300% which causes pulverization of active material and loss of electric contact with current collectors [5]. Nevertheless, commercial manufacturers have started to incorporate up to 12 wt.% of silicon in a graphite base to improve capacity of the resultant composite anode while benefitting from stability of a traditional carbon-based material [6].Ensuring safety of LIBs is of prime importance, particularly for energy intensive applications such as EVs. It is also crucial to check systematically how the supposedly advanced batteries behave in different environments [7]. With this purpose in mind, comprehensive cycle life tests of 18650-type commercial cells with Ni-rich NCA cathode and Si-graphite composite anode were conducted in the present study. In addition to room-temperature environment, cell performance and degradation behavior were investigated at both the temperature extremes, 0 and 45 °C using the maximum (dis)charge current, specified by the manufacturer. Key aspects describing evolution of electrode morphology over cycle life e.g. porosity changes, SEI growth and elemental compositions were captured using impedance spectroscopy and physical characterization techniques. Comparisons were made to the degradation behavior of 18650-type commercial NMC/Si-graphite cell, recently tested by Smith and co-workers [8]. Counter-intuitively, the NCA cells analysed herein demonstrated better capacity retention and a significantly longer cycle life than the aforementioned NMC/Si-graphite cells in room temperature (1000 cycles Vs. 250 cycles); making the concept of “second-life applications” seem techno-economically viable.

Surface Modification of Cathode Via Precursor Coating for All-Solid-State Batteries

Li-ion batteries (LIBs) have been used widely for mobile device, electrical vehicle (EV), and energy storage system (ESS). As the expansion of application fields, unstable safety of LIBs attributed to the flammable organic liquid electrolyte has been considered as a serious issue. All solid state batteries (ASSBs) based on nonflammable inorganic solid electrolyte could be a good solution for this issue. Until now, a lot of inorganic ionic conductors has been studied for using as solid electrolytes of ASSBs. Sulfides are promising candidates for solid electrolyte for ASSBs due to their comparable ionic conductivity to liquid electrolyte. Moreover, they can be easily assembled with electrodes due to their ductility. However, ASSBs based on sulfide electrolyte has several problems such as poor rate capability and unstable cyclic performance, which are mainly attributed to the side reaction between oxide cathodes and reactive sulfide electrolyte. Surface modification of cathode using stable materials against sulfides has been known as an effective approach for overcoming this problem. In this study, the cathode material was modified using several oxides. Specially, the coating process was started from the precursors instead of as-prepared cathodes to obtain more homogeneous coating layer. The surface modified cathodes are expected to show improved cyclic performance and rate capability due to the effect of surface modification.