Magnesium battery systems present a distinct safety profile compared to conventional lithium-based technologies, with inherent advantages and challenges rooted in their chemistry and material behavior. The evaluation of their safety characteristics focuses on thermal stability, reaction pathways under abuse conditions, and flammability risks, along with design strategies to address these concerns.

Thermal stability is a critical factor in battery safety. Magnesium batteries exhibit higher thermal stability than lithium-ion systems due to the intrinsic properties of magnesium metal. The melting point of magnesium is 650 degrees Celsius, significantly higher than lithium's 180 degrees Celsius, reducing the risk of internal short circuits caused by dendrite penetration at elevated temperatures. Additionally, magnesium does not form dendritic structures as readily as lithium, which mitigates one of the primary failure modes in lithium-metal batteries. The solid electrolyte interphase (SEI) in magnesium systems is more stable under thermal stress, though its exact composition and behavior depend on the electrolyte formulation. Unlike lithium-ion batteries, where organic carbonate-based electrolytes decompose exothermically above 60-80 degrees Celsius, magnesium electrolytes often employ less volatile solvents, such as ethers or ionic liquids, which exhibit higher thermal decomposition thresholds.

Under abuse conditions, such as overcharging, short-circuiting, or mechanical damage, the reaction pathways in magnesium batteries differ from those in lithium-based systems. During overcharging, magnesium batteries show reduced gas generation compared to lithium-ion cells, where electrolyte decomposition produces flammable gases like hydrogen, carbon monoxide, and carbon dioxide. Magnesium systems generate minimal gas, primarily due to the absence of solvent reduction reactions that plague lithium electrolytes. In short-circuit scenarios, the lower redox potential of magnesium (-2.37 V vs. SHE) compared to lithium (-3.04 V vs. SHE) results in a less aggressive electrochemical reaction, reducing the instantaneous heat release. Mechanical abuse, such as nail penetration or crushing, poses a lower risk of thermal runaway in magnesium batteries because the metal does not react as violently with air or moisture as lithium. However, magnesium powder or thin foils can still ignite when exposed to open flames or high temperatures, necessitating careful handling in cell design.

Flammability risks in magnesium batteries are primarily associated with the metal itself rather than the electrolyte. Magnesium is classified as a flammable solid, and fine particles or thin films can ignite at temperatures above 450 degrees Celsius in air. This contrasts with lithium-ion batteries, where the organic electrolytes are the primary fire hazard. The combustion of magnesium produces intense heat and bright light, but it does not involve the explosive gas generation seen in lithium battery fires. To mitigate these risks, cell designs often incorporate flame-retardant additives in the electrolyte or separators, such as phosphorus-based compounds, which can suppress ignition. Encapsulation of magnesium electrodes in non-combustible matrices, such as ceramic-coated separators or metal oxide layers, also reduces direct exposure to oxygen.

Design approaches to enhance safety in magnesium batteries focus on material selection and cell architecture. One strategy involves the use of non-flammable electrolytes, such as inorganic ionic liquids or solid-state magnesium conductors, which eliminate the risk of solvent fires. Another approach is the integration of thermally stable cathodes, like transition metal oxides or sulfides, which do not release oxygen during decomposition—a common issue with lithium cobalt oxide or nickel-rich cathodes. The mechanical robustness of cell casings is also critical; reinforced aluminum or steel housings can withstand internal pressure buildup and prevent external oxygen ingress during thermal events. Current collectors and electrode substrates made of refractory materials, such as titanium or tungsten, further enhance thermal tolerance.

A key advantage of magnesium batteries is their compatibility with aqueous electrolytes in certain configurations, though this requires careful pH control to prevent hydrogen evolution. Aqueous systems inherently reduce flammability risks compared to organic solvents, but they introduce challenges related to corrosion and passivation. Non-aqueous magnesium electrolytes, while more stable, must be purified to remove reactive impurities like water or halides, which can degrade cell performance and safety.

In summary, magnesium battery systems offer several safety advantages over lithium-based technologies, including higher thermal stability, reduced gas generation, and lower reactivity under abuse conditions. However, the flammability of magnesium metal itself requires specific mitigation strategies in cell design. By leveraging non-flammable electrolytes, stable electrode materials, and robust mechanical enclosures, magnesium batteries can achieve a safety profile that complements their potential for high energy density and cost-effectiveness. These design considerations are critical for advancing magnesium battery technology toward commercial viability without relying on battery management systems for primary safety functions.