Here we discuss effects in Li-ion batteries in which local nonuniformities in battery construction or mechanical stress can couple into the electrochemical processes of the system and lead to accelerated decay and safety concerns. We present the relevant mechanisms and discuss methods of mitigating these effects in real systems.

Frequency responses computed from transfer functions convey important information about system dynamic behavior. Applied to batteries, we normally consider electrochemical impedance spectroscopy (EIS), a spectral characterization of cell output voltage to input current. This talk expands the standard analysis by first presenting a full-order (pseudo-2D) model incorporating a double-layer effect and then derives closed-form transfer functions enabling the calculation of individual frequency responses for internal electrochemical variables.

Electric vehicle energy storage systems using lithium-ion batteries require constant monitoring to ensure safe and reliable performance. Limits on applied current, cell voltage and temperature are essential to meeting these objectives. This presentation describes a novel application of model predictive control and a sigma-point Kalman filter to produce optimal estimates of charge/discharge power, which adhere to constraints on key problem variables to ensure safe and efficient operation.

This work examines the results of accelerating rate calorimetry testing on different lithium-ion cathode chemistries (LCO, NCA, NMC, LFP), different formats (18650, pouch, large-format cylindrical), and states of charge to understand how ARC results are impacted by both energy density and total energy. Also studied is how thermal runaway is impacted by energy in general, looking at both the total energy release during thermal runaway, as well as the peak heating rates observed.

The increased demand for reliable portable medical devices operating for extended periods on a single charge is a great fit for both lithium primary (single-use) and lithium-ion (rechargeable) battery technologies. The benefits of these technologies include: 1) larger power and energy densities; 2) low self-discharge rates; and 3) a variety of form factors and chemistries that are compatible for different requirements. However, for both performance and safety, lithium battery technologies require active battery management. The battery management system (BMS) performs a number of functions. Some safety-related functions include preventing cell overcharge, overdischarge, and operation outside allowable temperatures. Some performance-related functions include estimating the battery’s state of charge (SOC), tracking the battery’s state of health (SOH), and electrical balancing of cells in strings (balancing is also important for safety). The purpose of this presentation is to examine physics-based requirements for battery management systems in medical devices and to understand how these requirements vary over the lifespan of the battery system.

The lithium-ion battery degrades over time, which compromises its electrochemical performance and mechanical integrity, and eventually battery safety. An enhanced fast-charging strategy can overcome these limitations. This work proposes a novel fast-charging strategy to charge lithium-ion batteries safely. This strategy contains a voltage-spectrum-based charging current profile, which is optimized through an optimization framework with physics-based battery models and a genetic algorithm.

The transportation authorities (DoT and ICAO) require that lithium-ion cells and batteries should be shipped at states of charge that are 30% or less. Research in the area of safety versus states of charge is not prevalent and not much data can be found in the literature. UL has carried out an extensive test program that includes cells with different lithium-ion cathode chemistries, different form factors and two different battery designs. Cell and battery types included those that were considered counterfeit also. The trends observed in safety with states of charge for cells and battery designs will be presented.

Passive and active thermal management of lithium ion cells determines not only the performance envelope but also the fire propagation patterns. With effective removal of heat from cells, a lithium ion battery pack can deliver high power, be charged quickly and minimize balancing activity due to lower temperature differentials across the pack. Indirectly these traits also enhance life and reduce maintenance costs. The effectiveness of immersive cooling is demonstrated in this work using AmpCool™ from Engineered Fluids as an example. 9PS1 modules were tested when a single cell was subjected to nail penetration. The propagation of fire and thresholds of inception and end were flagged by analyzing the voltage and temperature patterns with and without the presence of the immersive coolant. 

The stability of redox active molecules is a paramount property that dramatically affects the cycling performance in redox flow batteries. Computationally, it requires a huge amount of resources to exhaustively iterate all the possible degradation pathways in order to estimate the stability of active species, such as radical cations. QSAR, or quantitative structure–activity relationship, provides an interesting approach to correlate chemical structures and properties based on the idea that property changes are all coming from structure modifications.

Battery module/pack testing is critical across all stages of battery R&D and production, but traditional methods of battery testing are an extremely time-consuming and costly challenge. Today, testing requires more flexibility and scalability to meet the growing demands of electrification and high performance. This presentation will equip battery manufacturers with cutting-edge technologies, trends, and test solutions for battery module/pack testing.

Michael will be available to take your questions from his live tutorial given earlier in the day. A recording of the tutorial is scheduled to be available for on demand viewing by 10:00am on July 30, 2020 and the original live broadcast will take place at 7:30am - All Times Eastern Daylight (UTC-04:00)