Lithium Battery Off Gassing: Biological Effects and Safety

Lithium-ion batteries are widely used in electronics, electric vehicles, and energy storage systems. However, under conditions such as overcharging, overheating, or physical damage, these batteries can release gases through off-gassing, raising concerns about health risks and safety hazards.

Understanding lithium battery off-gassing effects is crucial for minimizing exposure risks and improving safety measures.

Composition Of Emitted Gases

When lithium-ion batteries experience thermal runaway or mechanical failure, they release a complex mixture of gases, many of which pose toxicological and safety concerns. The composition of these emissions depends on the battery’s electrolyte formulation, additives, and failure conditions. One of the most hazardous components is hydrogen fluoride (HF), a highly corrosive and toxic gas that forms when lithium hexafluorophosphate (LiPF₆), a common electrolyte salt, decomposes in moisture. HF concentrations can reach dangerous levels in confined spaces, causing severe respiratory and dermal irritation (Andersson et al., 2016, Journal of Hazardous Materials).

Beyond HF, off-gassing produces volatile organic compounds (VOCs) and flammable gases. Carbon monoxide (CO) and carbon dioxide (CO₂) result from the breakdown of organic solvents like ethylene carbonate and dimethyl carbonate, which are widely used in electrolytes. CO is a well-documented asphyxiant that binds to hemoglobin with an affinity over 200 times greater than oxygen, leading to hypoxia at high concentrations (Ernst & Zibrak, 1998, New England Journal of Medicine). Hydrocarbons such as methane, ethane, and ethylene add to the flammability of emissions, increasing fire and explosion risks in poorly ventilated environments.

Phosphorus oxyfluoride (POF₃) and other fluorinated compounds arise from the thermal degradation of electrolyte salts and fluorinated binders. These compounds hydrolyze into HF upon contact with atmospheric moisture, intensifying their corrosive effects. Exposure to fluorinated decomposition products can cause pulmonary edema and long-term respiratory complications, particularly in occupational settings where battery failures are frequent (Ohsaki et al., 2005, Electrochimica Acta).

Mechanisms Of Electrolyte Decomposition

Lithium-ion battery electrolyte breakdown is driven by thermal, electrical, and mechanical stressors. The instability of organic carbonate solvents and lithium salts leads to exothermic reactions, generating gaseous byproducts that contribute to pressure buildup and off-gassing. Lithium hexafluorophosphate (LiPF₆), a widely used electrolyte salt, decomposes readily in moisture, releasing HF and other fluorinated compounds.

At temperatures beyond 80–100°C, organic carbonate solvents such as ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) break down through reductive and oxidative decomposition. Reductive decomposition at the anode produces hydrocarbons like methane, ethane, and ethylene, while oxidative breakdown at the cathode releases CO₂ and carbonyl compounds. Once thermal runaway begins, heat generation surpasses dissipation, driving the battery toward failure.

LiPF₆ decomposition plays a key role in electrolyte breakdown due to its instability. Even under normal conditions, it undergoes slow hydrolysis, forming phosphorus pentafluoride (PF₅) and HF. At elevated temperatures, this reaction accelerates, creating phosphorus oxyfluoride (POF₃) and other reactive fluorinated species, which not only increase toxicity but also catalyze further electrolyte degradation. HF exposure accelerates solid electrolyte interphase (SEI) dissolution, exposing fresh lithium surfaces to further parasitic reactions and increasing flammable gas release (Aurbach et al., 2002, Journal of the Electrochemical Society).

Electrolyte decomposition is worsened by interactions with electrode materials, especially during overcharging or internal short circuits. Overcharging induces cathode breakdown, releasing oxygen, which reacts with electrolyte solvents to produce carbon monoxide and other hazardous compounds. Mechanical damage compromising the separator can cause direct contact between the anode and cathode, triggering localized heating and rapid electrolyte degradation. Nickel-rich cathodes exacerbate this issue by undergoing oxygen evolution at lower temperatures, increasing thermal runaway risk (Kim et al., 2019, Energy & Environmental Science).

Biological Interactions With Off-Gassed Compounds

Inhalation and dermal exposure to off-gassed compounds can cause severe health effects, particularly targeting the respiratory system, mucous membranes, and skin. Hydrogen fluoride (HF) is among the most hazardous emissions, readily dissolving in water to form hydrofluoric acid upon contact with bodily fluids. Unlike many acids that cause surface burns, HF penetrates deeply into tissues, binding with calcium and magnesium ions, disrupting cellular function, and leading to systemic toxicity. Even low-concentration exposure can cause delayed but severe effects, including necrosis and electrolyte imbalances that may trigger cardiac arrhythmias (Braun et al., 2017, Toxicology Letters).

Volatile organic compounds (VOCs) such as formaldehyde, acetaldehyde, and benzene present additional health risks. These compounds, formed from the breakdown of carbonate-based electrolytes, have cytotoxic and carcinogenic properties. Formaldehyde, classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC), is linked to nasopharyngeal cancer and hematologic malignancies (IARC Monographs, 2012). Short-term inhalation can cause headaches, dizziness, and airway inflammation, while chronic exposure increases the risk of pulmonary fibrosis and oxidative DNA damage. The small molecular size and lipophilic nature of these VOCs enable them to penetrate cell membranes, interfering with normal metabolic processes and exacerbating lung inflammation.

Carbon monoxide (CO) in battery emissions further heightens health risks due to its high affinity for hemoglobin. By forming carboxyhemoglobin, CO displaces oxygen in the bloodstream, causing hypoxic injury in vital organs. Even moderate CO exposure—at levels as low as 100 parts per million (ppm)—impairs cognitive function and reduces aerobic capacity, particularly in individuals with cardiovascular conditions (Raub & Benignus, 2002, Environmental Health Perspectives). Higher concentrations can result in irreversible neurological damage, with symptoms including memory deficits, mood disturbances, and motor dysfunction. Lithium battery failures often occur in enclosed spaces, increasing the potential for CO accumulation and occupational hazards.

Environmental Conditions Influencing Gas Formation

The rate and composition of emitted gases depend heavily on environmental factors, with temperature playing a dominant role. Elevated heat accelerates electrolyte decomposition, rapidly increasing internal pressure. When battery temperatures exceed 150°C, thermal runaway becomes self-sustaining, drastically increasing gas emissions (Feng et al., 2020, Nano Energy). This risk is particularly concerning in high-temperature climates or poorly ventilated enclosures, where heat dissipation is limited. Even moderate temperature elevations—such as prolonged exposure to 60°C—can degrade electrolyte stability and trigger early-stage off-gassing.

Humidity also plays a significant role by facilitating lithium salt hydrolysis, particularly LiPF₆. In high-moisture environments, the reaction between LiPF₆ and water accelerates HF generation, increasing emission toxicity. Industrial settings or storage areas with elevated humidity create conditions where battery degradation occurs faster, emphasizing the need for controlled storage environments. Similarly, atmospheric oxygen levels contribute to the oxidative breakdown of organic solvents, further influencing emitted gas composition.