Battery aging at sub-zero temperatures presents unique challenges distinct from those observed at elevated temperatures. While high-temperature degradation primarily involves electrolyte decomposition and solid electrolyte interphase (SEI) growth, cold-temperature aging mechanisms revolve around electrolyte viscosity changes, lithium plating kinetics, and anode overpotential increases. Understanding these differences is critical for developing batteries capable of enduring harsh environments without premature failure.

At sub-zero temperatures, electrolyte viscosity rises significantly, impeding ion transport. The increased resistance reduces ionic conductivity, slowing charge transfer reactions. For example, a conventional lithium-ion battery electrolyte with 1M LiPF6 in ethylene carbonate and dimethyl carbonate may experience a conductivity drop from approximately 10 mS/cm at 25°C to below 1 mS/cm at -20°C. This increased viscosity forces the battery to operate at higher overpotentials to maintain the same current density, accelerating degradation.

Lithium plating becomes a dominant aging mechanism in sub-zero conditions. As charge transfer resistance increases, the anode potential drops closer to lithium deposition thresholds. Metallic lithium forms on the graphite surface instead of intercalating, leading to irreversible capacity loss. Plating is exacerbated during charging, particularly at high rates, where ion diffusion cannot keep pace with electron transfer. Studies show that charging at 0.5C below -10°C can induce plating within just a few cycles, whereas the same rate at 25°C may not trigger deposition. The plated lithium reacts with the electrolyte, forming additional SEI layers that consume active lithium and increase impedance.

Anode overpotential increases disproportionately at low temperatures due to sluggish kinetics. Graphite anodes exhibit higher polarization than cathodes under cold conditions, shifting the voltage window unfavorably. This imbalance strains the cell, reducing usable capacity and increasing heat generation. Over repeated cycles, the accumulated overpotential contributes to accelerated capacity fade. In contrast, high-temperature aging typically involves cathode degradation through transition metal dissolution or SEI thickening on the anode, rather than kinetic limitations.

Electrolyte composition plays a crucial role in sub-zero aging. Linear carbonate solvents like ethyl methyl carbonate improve low-temperature performance by reducing viscosity, but they may compromise high-temperature stability. Additives such as fluoroethylene carbonate can suppress lithium plating by stabilizing the anode interface, though their effectiveness diminishes as temperatures drop further. Solid-state electrolytes face even greater challenges, as their already-limited ionic conductivity plummets in the cold, making them prone to rapid aging unless specifically formulated for low-temperature operation.

High-temperature aging follows fundamentally different pathways. Above 40°C, electrolyte oxidation and SEI growth accelerate, consuming lithium inventory and increasing cell resistance. Transition metals leach from layered oxide cathodes, migrating to the anode and catalyzing further side reactions. These processes are thermally activated, following Arrhenius kinetics, where each 10°C rise approximately doubles degradation rates. In contrast, sub-zero aging is dominated by transport limitations rather than chemical reactivity, making it more sensitive to operational conditions like charge rate and voltage limits.

Cycling protocols significantly influence low-temperature aging outcomes. Partial state-of-charge cycling reduces lithium plating risk compared to full cycles, as the anode remains at moderate potentials. However, even shallow cycles at high rates can induce degradation when temperatures fall below -10°C. Calendar aging at sub-zero temperatures shows different characteristics than cycling aging, with slower SEI growth but increased vulnerability to lithium plating upon subsequent charging. High-temperature calendar aging, by comparison, continuously degrades the cell through electrolyte decomposition regardless of cycling.

Materials selection can mitigate sub-zero aging. Silicon-containing anodes suffer less from plating due to their higher operating potentials, though they face other low-temperature challenges like particle fracture. Nickel-rich cathodes maintain better kinetics in the cold than iron or manganese-based alternatives, helping balance anode overpotentials. Electrolyte optimization remains the most direct approach, with low-viscosity solvents and targeted additives offering the greatest improvements in aging resistance.

Safety implications differ between temperature extremes. High-temperature failures typically involve thermal runaway from exothermic reactions, while sub-zero degradation risks lithium dendrite formation that may cause internal shorts upon warming. Both scenarios necessitate distinct mitigation strategies in battery management systems, with low-temperature operation requiring strict current limits and voltage controls.

Understanding these contrasting aging mechanisms informs better battery design and usage policies. Applications requiring cold-weather operation, such as electric vehicles in northern climates or aerospace systems, must account for sub-zero degradation in their lifetime predictions. Accelerated aging tests targeting these conditions should emphasize lithium plating and electrolyte transport limitations rather than relying on high-temperature protocols that simulate different failure modes.

Future research directions include developing electrolytes with simultaneously low viscosity and high thermal stability, as well as anode materials resistant to plating across wide temperature ranges. Advanced characterization techniques can help quantify lithium plating in real-time during low-temperature cycling, while modeling efforts should incorporate temperature-dependent kinetic limitations more accurately. By addressing these challenges, next-generation batteries can achieve longer lifetimes even under extreme cold conditions.