Wesley Chang

Significant progress has been made in understanding and engineering rechargeable lithium metal batteries. Here, I discuss ultrasound as a technique to probe cell-level dynamics for lithium metal batteries in liquid and solid electrolytes. Multiple imaging modalities provide information on physical properties of lithium metal cells, including electrode wetting and consumption, lithium microstructural change and gas evolution. In a first case study, I discuss correlations between ultrasonic transmission signals and lithium microstructure size in liquid electrolytes, as a function of stack pressure and temperature. Anode and cathode effects can be decoupled. In a second case, acoustic amplitude is used to detect void formation in solid-state electrolytes. Third, ultrasound is used to characterize the formation process for various anode-free cells, where the improved chemical and electrochemical stability of localized ether electrolytes is correlated with decreased rates of cell swelling and minimal gas formation. Ultrasonic characterization and imaging is a portable and non-invasive means of probing commercial lithium metal cells after manufacturing, during use, or at the end-of-service.

Lithium-metal batteries experience significant mechanical stress as lithium is plated and stripped from the copper current collector during charge and discharge, respectively. Minimizing the negative effects of this stress on cell’s capacity retention over its cycle life is paramount to propel the high-density chemistry to the mainstream. To address this, acoustics have recently emerged as a viable experimental tool to monitor chemo-mechanical properties*.* In this work, we probe the underlying effects of coupled transient phenomena previously reported for Lithium-ion cells. By complimenting physical parameters—Young’s Modulus and damping coefficient, extracted from operando acoustics and pressure measurements—with simulations, we demonstrate that transient chemo-mechanical properties are in part resultant of ionic gradients in the electrolyte. These findings are in agreement with and build upon previous work on the acoustic signals of electrolytes by Wang et al , where acoustics were leveraged to extract mechanical parameters in situ , and of Lithium-ion cells by Hodson et al , where nonlinearities in full-cell Lithium-ion acoustic signals were were hypothesized to be a result of electrolytes. Our results highlight the viability of acoustics as a valuable tool in battery research to non-invasively inspect transient phenomena in batteries.

A commercially relevant lithium metal battery is still hindered by issues such as rapid consumption of the electrolyte and an unstable interface. Relative success in stabilizing the solid-electrolyte-interphase and achieving higher Coulombic efficiencies has been found using organoborate electrolyte salts, highly fluorinated solvents, external pressure and surface modification strategies. However, initially dense close-packed plating does not necessarily exhibit structural or mechanical reversibility. Operando acoustic analysis is a reliable technique for interrogating physical changes within a closed-form battery. Specifically, the effective stiffness can be accurately measured to probe changes in the intrinsic material properties of plate metal. Stiffness, in addition to stress and strain, is an important metric in mechanical characterization of phase change or plate metal electrodes. Here, we describe recent efforts to diagnose common failure mechanisms using acoustics and extension of the technique to dynamically probe structural changes in plate metal anodes. Figure 1

It is well understood that lithium metal should not exist in lithium ion batteries, but high energy/high rate lithium ion cells did not seem to have gotten this memorandum. Dissection of commercial cells often indicates direct and indirect evidence of metallic lithium present in the battery. This lithium is often called "dead" lithium as it is considered no longer active. In this presentation we motivate the nomenclature zombie lithium because it is, in this construction, truly undead. Lithium metal that is present in lithium ion batteries is never completely isolated from the other activities of the cell, and as the cell ages, without proper understanding, the "dead" lithium can suddenly arise and impact the cell is decidedly negative ways. In this presentation we will review and (try to) understand behavior of zombie lithium generated during the operation of a lithium ion battery and time scale and length scales of its impact across the cell and the system.

Finding low-cost energy storage solutions is critical to minimizing the curtailment of renewable electricity generation and matching diurnal variations in electricity demand and production. Continuum electrochemical modeling has shown that minimizing cell hardware and maximizing electrode thickness for low-cost cathode materials (LMO) can help to reduce cell costs to below $100/kWh. We demonstrate the relationships between electrode thickness, porosity, rate and cost in order to design sufficiently thick intercalation cathodes that meet the minimum rate capabilities for low-cost long-duration storage applications.