Lithium-metal batteries represent a promising advancement in energy storage technology due to their high theoretical energy density and potential for use in electric vehicles and aerospace applications. However, their performance at low temperatures, particularly below -20°C, presents significant challenges that must be addressed to ensure reliable operation in cold environments. This article examines the low-temperature behavior of lithium-metal batteries, focusing on electrolyte freezing points, charge transfer resistance, and lithium morphology changes, while contrasting these characteristics with conventional lithium-ion batteries.

One of the primary challenges for lithium-metal batteries at low temperatures is the electrolyte's tendency to freeze or become highly viscous. The electrolyte's freezing point is determined by its chemical composition, with conventional carbonate-based electrolytes commonly used in lithium-ion batteries freezing at around -20°C to -30°C. In contrast, lithium-metal batteries often employ ether-based electrolytes, which generally exhibit lower freezing points, typically below -40°C. However, even with these lower freezing points, the ionic conductivity of ether-based electrolytes still decreases significantly as temperatures drop, leading to reduced battery performance. The increased viscosity of the electrolyte at low temperatures impedes ion transport, resulting in slower reaction kinetics and diminished power output.

Charge transfer resistance is another critical factor affecting low-temperature performance. In lithium-metal batteries, the charge transfer resistance at the electrode-electrolyte interface increases substantially as temperatures decrease. This phenomenon is particularly pronounced in lithium-metal anodes, where the charge transfer resistance can rise by an order of magnitude when the temperature drops from 25°C to -20°C. The increased resistance is attributed to the sluggish desolvation of lithium ions and the reduced mobility of ions through the solid electrolyte interphase (SEI) layer. In conventional lithium-ion batteries, graphite anodes exhibit similar increases in charge transfer resistance at low temperatures, but the effect is less severe due to the more stable SEI layer formed on graphite compared to lithium metal. The higher charge transfer resistance in lithium-metal batteries leads to significant polarization during charging and discharging, reducing efficiency and capacity.

Lithium morphology changes at low temperatures further complicate the performance of lithium-metal batteries. At subzero temperatures, lithium deposition tends to become more dendritic and inhomogeneous. The reduced ion mobility and increased charge transfer resistance promote uneven lithium plating, leading to the formation of needle-like dendrites. These dendrites can penetrate the separator, causing internal short circuits and potential thermal runaway. In contrast, lithium-ion batteries with graphite anodes do not face this issue, as lithium intercalation occurs without metal deposition. The absence of lithium plating in conventional lithium-ion batteries makes them inherently more stable at low temperatures, though they still suffer from capacity loss due to slowed kinetics.

The interplay between electrolyte properties, charge transfer resistance, and lithium morphology creates a complex challenge for low-temperature operation of lithium-metal batteries. While conventional lithium-ion batteries also experience performance degradation in cold environments, the mechanisms differ. Lithium-ion batteries primarily suffer from reduced ionic conductivity in the electrolyte and increased charge transfer resistance at the graphite anode, but they do not face the dendrite-related safety risks associated with lithium-metal batteries. Additionally, the capacity retention of lithium-ion batteries at -20°C is generally better than that of lithium-metal batteries, though both systems exhibit significant energy and power losses.

Efforts to improve the low-temperature performance of lithium-metal batteries have focused on electrolyte engineering, SEI modification, and advanced electrode designs. Electrolyte additives that lower freezing points and enhance ion transport have shown promise in reducing charge transfer resistance. Furthermore, the development of artificial SEI layers with improved low-temperature stability can mitigate lithium dendrite growth. While these advancements are encouraging, lithium-metal batteries still lag behind conventional lithium-ion batteries in terms of low-temperature reliability.

In summary, lithium-metal batteries face substantial hurdles when operating at temperatures below -20°C due to electrolyte freezing, increased charge transfer resistance, and unfavorable lithium deposition behavior. These challenges are more severe than those encountered by conventional lithium-ion batteries, which benefit from more stable electrode materials and absence of lithium plating. Addressing these issues will be crucial for enabling the widespread adoption of lithium-metal batteries in applications requiring reliable performance in cold climates. Future research must continue to explore innovative solutions to enhance low-temperature behavior while maintaining the high energy density that makes lithium-metal batteries an attractive technology.