Lithium dendrites are needle-like structures that form during the electrodeposition of lithium metal. These whiskers complicate the use of lithium metal as an anode in lithium batteries because they can puncture the separator and short circuit the battery. In addition, the large surface area and poor adhesion of the deposit contributes to loss of coulombic efficiency. The effect of alkali and alkaline earth metal ions on the morphology of electrodeposited lithium metal has been studied. Varying concentrations of alkali and alkaline earth metal ions were added to a 1 M lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) trimethylbutylammonium bis(trifluoromethanesulfonyl)imide (N 1114 -TFSI) electrolyte. Lithium metal was electrodeposited from each electrolyte and examined ex-situ by scanning electron microscopy (SEM). Alkali metal ions, with the exception of sodium, had little or no effect on the deposited lithium morphology. However, alkaline earth metal ions at 0.05 M concentration significantly reduced the occurrence of dendrites. When the concentration of the alkaline earth metal ions was increased to 0.1 M, dendrites were completely eliminated and lithium was deposited in a sphere-like morphology. Energy dispersive X-ray spectroscopy (EDX) showed that no alkaline earth metals were found in the sphere-like deposits, suggesting that dendrite mitigation occurred through an adsorption mechanism. Lithium-ion batteries based on graphite anodes have been commercialized and used in mobile devices due to their high power and energy density. The graphite anode operates close to its theoretical capacity of 329 mAh/g. Thus, to increase the energy density of the overall battery, a new anode material must be developed. Reducing lithium ions on a substrate, rather than intercalating them into graphite, raises the specific capacity of the anode to 3861 mAh/g and is compatible with existing cathodes and future high-voltage cathodes.Lithium-metal anodes suffer from low cycling efficiency for several reasons. First, the solid electrolyte interface (SEI) that forms on graphite anodes to protect the electrode from further reaction with the electrolyte, does not form as well on a metallic lithium surface. Second, the lithium metal anode undergoes extreme volume changes when going between the charged and discharged states, which can significantly disrupt the SEI during each cycle. Finally, when lithium metal is deposited on a substrate, such as during battery charging, lithium does not deposit as a dense, cohesive, planar layer, but rather deposits as needle-like structures, sometimes called dendrites, as shown in Figure 1.Adding SEI forming additives and restricting the battery to shallow discharge cycles can mitigate some of these problems, however, these restrictions are not desirable. Vinylene carbonate (VC) has been shown to be a valuable additive for lithium metal batteries, yielding higher efficiencies and increased cycle life.1,2 VC and other cyclic carbonates have been shown to form an SEI via ring-opening reactions tha...

Lithium-ion batteries are prevalent in every aspect of modern life (cell phones, laptops, electric vehicles, and energy storage systems for the electric grid). For all applications, the battery safety is an important consideration. Compared to numerous studies on the safety behavior of 18650-type cells, limited research has been conducted to characterize prismatic cells with their unique challenges including how electrode gapping, cycling history, electrolyte degradation, or lithium plating affect the safety. In this paper, a systematic study is reported on prismatic cells cycled at 0 °C, 23 °C, and 45 °C. The safety aspect of the cells with electrode gapping is evaluated using accelerating rate calorimetry (ARC). The evolution of gaps was monitored using X-ray computed tomography. Our study demonstrates that gaps are intrinsic even in fresh cells. The gaps can evolve during cycling and are closely related to the localized lithium plating and electrolyte degradation, which can be more severe for cells cycled at 45 °C. However, the safety behavior is not simply correlated to cell internal structure (e.g. gapping), or the amount of degradation products after cycling; the aging mechanism at different temperatures also plays an important role. Understanding the thermal stability of prismatic cells during their lifecycle is necessary for risk mitigation in numerous applications.

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An increasing demand to repurpose used lithium-ion batteries in secondary applications is driving the need to develop methods of evaluating the state-of-health of used batteries. In this paper, we discover a self-terminated end-of-charge temperature rise (ECTR) phenomenon in 18,650 lithium-ion cells, both recycled from the field and aged under controlled conditions in the lab. ECTR is characterized by an additional temperature rise near the end of the charging process and is accompanied by low coulombic efficiency. A higher charge rate and longer inactive time at low state-of-charge appear to increase the occurrence of ECTR. The intensity of ECTR is found to closely correlate with the excess charge capacity but is less affected by the charge current or cell impedance. ECTR is weakly dependent on the remaining cell capacity in recycled cells, and the controlled aging study shows that aging condition, not remaining capacity or internal resistance, determines the presence and intensity of ECTR behavior, which indicates that usable capacity or internal resistance should not be the single criterion to effectively evaluate the state-of-health of used cells intended for repurposing. We hypothesize that the origin of the ECTR is due to the formation of an internal lithium metal short that forms near the end of the charge process and self-terminates over time. The investigation of ECTR in this work provides a new criterion and approach to evaluate the state-of-health of cells required to safely handle aged/recycled cells.