Lithium-ion batteries experience gas generation during operation, particularly under conditions that promote lithium plating. This phenomenon becomes especially pronounced during fast charging, where high currents and elevated temperatures accelerate side reactions. The relationship between rapid lithium plating, localized heating, and gas production is complex but follows well-documented electrochemical and thermal principles.
Lithium plating occurs when lithium ions accumulate on the anode surface faster than they can intercalate into the graphite structure. This is driven by high charging currents (C-rates) and exacerbated by low temperatures. Plated lithium reacts with the electrolyte, forming solid electrolyte interphase (SEI) decomposition products and gaseous byproducts such as hydrogen, ethylene, and methane. Localized heating further intensifies these reactions by increasing the kinetics of parasitic processes.
The C-rate directly influences the extent of lithium plating. At moderate C-rates (below 1C), lithium intercalation dominates, and plating is minimal. However, as the C-rate increases beyond 1C, the anode polarization rises, reducing the overpotential available for intercalation. Studies show that at 2C, lithium plating becomes significant, and above 3C, it dominates the charge process. The plated lithium is highly reactive, especially in the presence of conventional carbonate-based electrolytes, leading to accelerated gas evolution.
Temperature plays a critical role in gas generation dynamics. At low temperatures (below 15°C), lithium-ion diffusion slows, increasing the likelihood of plating even at moderate C-rates. Below 0°C, the risk becomes severe, with studies indicating a 30-50% increase in gas production compared to room-temperature operation. Conversely, elevated temperatures (above 40°C) reduce plating but introduce other degradation pathways, such as electrolyte decomposition and SEI growth, which also produce gas. The interplay between C-rate and temperature creates a nonlinear relationship where intermediate conditions (high C-rate and moderate temperature) often result in the most severe gas generation due to combined plating and thermal effects.
Localized heating is a key amplifier of gas production. During fast charging, uneven current distribution leads to hot spots near plated lithium regions. These areas experience higher temperatures than the bulk cell, accelerating electrolyte breakdown and gas formation. Infrared thermography studies have shown temperature differentials of 5-10°C within a single cell under fast-charging conditions, with localized spikes exceeding 15°C in severe cases. The increased temperature raises the vapor pressure of volatile electrolyte components, further contributing to gas accumulation.
The composition of the gas depends on the electrolyte formulation and the extent of lithium plating. Common gases include CO2 (from carbonate reduction), H2 (from solvent decomposition), and light hydrocarbons (from electrolyte fragmentation). Quantitative gas chromatography measurements reveal that fast-charged cells can produce 2-5 times more gas than slowly charged counterparts, with the majority of gas generation occurring in the later stages of charging when plating is most severe.
Mitigating gas generation requires balancing C-rate and temperature. Active thermal management can reduce localized heating, while optimized charging profiles can minimize plating. However, these strategies fall under fast-charging protocols, which are outside the scope of this discussion. Instead, the focus remains on the fundamental mechanisms linking lithium plating, heat generation, and gas evolution.
In summary, rapid lithium plating during high C-rate charging, combined with localized heating, significantly accelerates gas production in lithium-ion batteries. The dependencies on C-rate and temperature follow predictable trends, with the most severe gas generation occurring under conditions that maximize plating while maintaining sufficient thermal energy to drive side reactions. Understanding these relationships is critical for designing batteries that minimize gas-related degradation without compromising performance.
The quantitative aspects of this phenomenon are supported by electrochemical testing and gas analysis, confirming that the interplay between plating and heating is a primary driver of gas evolution in fast-charged lithium-ion cells. Future research may explore alternative materials and cell designs that inherently resist plating and thermal imbalances, reducing gas generation at its source.