Scalable and Non-Destructive Analysis of Battery Degradation and Performance

Abstract

Electrochemical processes occurring during battery operation are highly complex. Thermodynamic, kinetic and transport-based phenomena all play a significant role in the dynamic evolution of the time-based electrochemical response of any battery system. Researchers have long sought to quantify these various interconnected phenomena, but to-date elucidating the role these mechanisms play in the performance of battery systems has been challenging or impossible. To aid researchers in uncovering the mechanistic behavior of their systems, we have developed a novel testing protocol and corresponding data analysis method that is scalable and non-destructive (SAND). This protocol and analysis can be applied to any battery system, in any form factor, at any point in the battery life cycle; including R&D, manufacturing, and second life battery screening to name a few.The testing protocol is based on a series of galvanostatic current pulses at a variety of currents and/or times. By utilizing the natural differences in time-constant of the various electrochemical phenomena inside a battery, this technique can probe each mechanism to glean novel insight using standard battery cycling equipment. Specifically, the insights this technique can provide include: the electrochemical potential of each phase during lithiation and delithiation quantification of electrode kinetics at various states-of-charge (including exchange current density estimation from the Butler-Volmer model)quantitative estimation of transport-based polarization losses from both the electrodes and the electrolyte. This analysis provides an un-parallelled level of mechanistic insight into the inner workings of any battery, at any point, spanning small-scale R&D cells to large format cells in mass production.To demonstrate the capabilities of this technique this presentation will focus on the analysis of multiple cells (same model) from a Tier 1 supplier containing a lithium transition metal oxide cathode material cycled at various temperatures. These results have led to an extensive set of conclusions. For brevity a few of these conclusions are: The initial exchange current density of these cells is calculated to be 25.5 A/m2. The H2→H3 phase transition during charging is the least efficient phase, exhibiting the largest power loss during chargingThe inefficiencies in the H2→H3 phase transition are dominated by solid-state lithium atom diffusion within the electrodes. At low current densities the overpotential associated with transport is the dominant source of losses, while at higher currents kinetic overpotentials become the dominant source. In summary, we have developed a novel characterization technique requiring only standard battery cycling equipment that can be easily and quickly performed by researchers around the world. Whether on small-scale coin cells or large-format pouch cells, the analysis from this technique will give the battery community insight into the thermodynamic, kinetic, and transport properties of their system. Moreover, this technique can be applied in a variety of contexts related to battery development, including understanding degradation mechanisms, performing root-cause analysis of manufacturing defects, or providing more accurate parameters for computational modeling.