Probing the Thermal Safety of Li Metal Batteries

Abstract

Li metal batteries (LMBs) with high energy density electrodes have emerged as the primary candidate for next-generation batteries owing to its superiority over conventional Li-ion technology. However, the safe operation of these systems under thermal abuse conditions remains primary concern regardless of the tremendous efforts to prevent short circuits through dendrite formation. In this context, we employ differential scanning calorimetry technique to investigate the thermal stability of Li-S and Li-NMC532 metal batteries. The calorimetric measurements identify separator melting together with anode-centric thermal degradation reactions as the primary mechanism of thermal runaway. Separator with poor thermal stability (low melting point), could instigate an internal short circuit that leads to exponential temperature rise due to the rapid release of electrical energy. An in-house physicsbased modeling technique utilizes the knowledge of thermal stability at the materials level to predict the thermal safety of LMBs for pouch cell configuration. Simulations reveal that the thermal stability of the separator and parasitic reactions at the anode (Li metal) dictate the critical onset temperature of thermal runaway in Li metal batteries. The severity of thermal runaway can be modulated by carefully designing (capacity loading ratio (N/P)) the thickness of metal anode and advanced separator with better thermal stability.

From material properties to multiscale modeling to improve lithium-ion energy storage safety

“…Figure 3g demonstrates applying these same techniques of extracting parameters from DSC to a range of materials followed by parameter sweeps that map out the space of safe cell capacity/operational space; here, that parameter space is described in terms of predicted response in oven tests as a function of cell capacity. 10,55…”

“…56 (g) Thermal safety maps for cells with specific cell chemistry and capacity. 10,55 carbon, and spiky carbon) at the particle surface scale (Figure 4a) is shown to influence intercalation dynamics, electrochemical performances, and thermal runaway propensity. 56 The potential evolution of spiky carbon is closer to theoretical open-circuit voltage (OCV) than spherical carbon, indicating more lithium storage, the deferred onset of adverse lithium plating, and a lower side reaction rate.…”

“…Materials science also comes into other processes leading toward the initial breakdown of kinetic and transport barriers. For example, desirable fast charging can lead to lithium dendrite growth that can penetrate separators and induce energy release via a short circuit; 4,[6][7][8][9] separator failure/melting can have a similar effect 6,7,10 . Mechanical strain might be associated with changes in transport properties including particle cracking or strain induced defects; these topics arise in anode passivation and are significant in some cathode failure modes.…”

“…(f) Oven test modeling using extracted reaction kinetics from (e) 56. (g) Thermal safety maps for cells with specific cell chemistry and capacity 10,55.…”

Dendrite-Suppressing Separator with High Thermal Stability Modified by Beaded-Chain-Like Polyimide Coating for a Li Metal Anode

“…To prevent the penetration of Li dendrites, separators with high mechanical strength or Li-reactive separators are adopted to serve as a physical barrier or consume the prolonged Li metal once the tip of dendrites reaches the separator. , Besides short circuit, thermal runway also is considered as a safety hazard of the Li metal anode, especially at high temperatures. The efforts in heat management by separators can be divided into three catalogs as the following: (1) bestowal outstanding thermal conductivity on separators to provide a homogeneous thermal atmosphere and prevent the “hot spots” during Li plating/stripping; (2) improvement in thermal stability to maintain the structural integrity of separators to prevent thermal shrink and thermal runaway at elevated temperatures; , and (3) adoption of a thermal-shutdown separator to block the pores when overheating occurs …”