Abstract
Li-ion batteries are prone to thermal transients imposed by external environmental conditions and/or operationally-induced self-heating characteristics. The material properties, form factor, and implemented cooling strategy of a battery influence the severity and behavior of thermal transients. In contrast to equilibrated low temperatures (0˚C), both substantial and mild (40 to 0˚C and 10 to 0˚C) temporally transient thermal conditions, result in approximately half of the Li+ ions plate as lithium metal at the anode, as opposed to intercalating, in the first charge. This quantity of plated lithium accelerates capacity loss in subsequent cycles and causes rapid onset of jellyroll collapse (cycles 5-8). The plating process induced by charging under a thermal transient causes a unique drop in voltage during charging, resulting in a negative differential voltage, which is not observed in subsequent cycles when the cell temperature has reached thermal equilibrium or in any equilibrium condition. Because a negative differential voltage is distinct, it provides route for detection to prevent rapid degradation and compromised safety. Accelerated rate calorimetry assesses cell safety after substantial plating and jellyroll collapse induced by charging under a temporally thermal transient condition. Self-heating begins at temperatures as low as 35˚C and can wall rupture provides risk of propagation failures in battery packs. Charging during thermal transients is identified as a plating-prone condition that alters the long-term performance and safety of Li-ion batteries. This work exemplifies the importance of understanding the role of thermal transients in pack assemblies to enable safe operation.
Highlights
Electrochemical behaviors are strongly coupled with thermal conditions (Rodrigues et al, 2017; Mistry et al, 2018)
Since the cells subjected to a temporally thermal transient condition during their first charge show distinct electrochemical behaviors during their first cycle in comparison to relevant equilibrium conditions, we examined the long term effects of these behaviors on cell performance
We determine that a single charge of a commercial Li-ion battery while its temperature is decreasing temporally toward 0◦C induces lithium plating which causes early loss of capacity, earlier onset temperature of thermal runaway, and higher heat generation temperature during thermal runaway
Summary
Electrochemical behaviors are strongly coupled with thermal conditions (Rodrigues et al, 2017; Mistry et al, 2018). Temperature variations alter the kinetics of redox processes (Nernst equation) and material properties that influence mass transport, for example electrolyte viscosity. These temperature variations can permit undesirable behaviors such as lithium plating and excessive solid-electrolyte interphase (SEI) growth. Low temperatures (Love et al, 2015), high charging rates (C-rates) (Waldmann et al, 2018), and spatial thermal gradients (Carter and Love, 2018) are known to enable lithium plating, a phenomenon often blamed for Li-ion battery failures. High temperatures accelerate SEI growth and diminish performance (Rodrigues et al, 2017).
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