Marine battery systems face unique thermal management challenges due to the demanding operational environments of maritime applications. Effective thermal regulation is critical for maintaining performance, safety, and longevity, particularly in high-humidity conditions where thermal runaway risks are exacerbated. The requirements differ significantly between surface vessels and submerged applications, necessitating tailored solutions for conductive cooling, liquid cooling, and phase-change materials.

Conductive cooling is a common approach for marine batteries, particularly in surface vessels where weight and complexity must be minimized. This method relies on heat sinks or thermally conductive materials to dissipate heat from battery cells to the surrounding structure or cooling plates. Aluminum and copper are frequently used due to their high thermal conductivity, with aluminum offering a balance between performance and weight savings. In surface vessels, conductive cooling is often paired with passive air convection, though this becomes less effective in enclosed or high-temperature environments. For submerged applications, conductive cooling must account for the lack of air convection, requiring direct thermal pathways to the hull or dedicated heat exchangers. The thermal conductivity of seawater, approximately 0.6 W/m·K, is lower than that of metals but can still serve as a heat sink if properly managed. However, corrosion-resistant materials are essential to prevent degradation in saltwater environments.

Liquid cooling systems are more effective for high-power marine batteries, particularly in applications with sustained high loads or limited thermal dissipation options. These systems circulate a coolant—often a water-glycol mixture—through channels embedded in or adjacent to the battery modules. In surface vessels, liquid cooling can leverage seawater as a secondary heat sink, reducing the need for additional refrigeration systems. Pump power and coolant flow rates must be optimized to balance thermal performance with energy efficiency. For submerged applications, liquid cooling becomes more complex due to pressure differentials and the need for leak-proof systems. Closed-loop designs are mandatory to prevent seawater intrusion, and titanium or high-grade stainless steel is often used for coolant lines to withstand corrosion. Data from naval battery systems indicate that liquid cooling can maintain cell temperatures within 5°C of the optimal range even under continuous discharge rates of 2C or higher.

Phase-change materials (PCMs) offer an alternative for thermal regulation, particularly in applications where passive cooling is preferred. PCMs absorb heat as they transition from solid to liquid, providing a buffer against temperature spikes. Paraffin-based materials with melting points between 25°C and 50°C are commonly used, as they align with the optimal operating range of most lithium-ion batteries. In surface vessels, PCMs can reduce reliance on active cooling systems, lowering energy consumption. However, their effectiveness diminishes in prolonged high-load scenarios unless paired with supplemental cooling. For submerged applications, PCMs must be carefully encapsulated to prevent leakage under pressure and humidity. Recent advancements include composite PCMs enhanced with thermally conductive fillers like graphite or metal foams, which improve heat distribution while retaining energy absorption capabilities.

Thermal runaway prevention is a critical concern for marine batteries, especially in high-humidity conditions where moisture can accelerate cell degradation or create short-circuit risks. Surface vessels are exposed to varying humidity levels, requiring robust sealing and desiccant systems to keep battery enclosures dry. Battery management systems (BMS) must monitor humidity and temperature in real-time, triggering cooling or load reduction if thresholds are exceeded. Submerged applications face even greater humidity challenges, as any breach in the battery housing can lead to catastrophic failure. Hermetic sealing and pressurized enclosures are standard, with redundant moisture sensors providing early warnings. Thermal runaway propagation can be mitigated by incorporating flame-retardant additives in electrolytes or using ceramic separators with high thermal stability. Data from marine battery tests show that cells with ceramic separators exhibit a 30% reduction in thermal runaway propagation speed compared to standard polyolefin separators.

Surface vessels and submerged applications also differ in their thermal regulation priorities. Surface vessels prioritize weight and energy efficiency, often favoring hybrid cooling systems that combine conductive and liquid cooling. The larger surface area allows for some passive heat dissipation, though active systems are still needed for high-power applications. Submerged systems, by contrast, must prioritize reliability and pressure resistance, often at the expense of weight. The lack of passive cooling options necessitates more aggressive active cooling, and the enclosed environment increases the risk of heat buildup. Pressure-tolerant designs must account for the additional stress on cooling system components, particularly in deep-sea applications where external pressures can exceed 50 atmospheres.

Quantitative studies on marine battery thermal management highlight the importance of material selection and system design. For example, lithium-ion batteries operating in humid environments show a 15% faster capacity fade when exposed to 85% relative humidity compared to dry conditions. Proper thermal regulation can mitigate this effect, with liquid-cooled systems demonstrating a 20% improvement in cycle life over passively cooled counterparts in the same environment. Accelerated aging tests further reveal that batteries maintained at 25°C exhibit twice the lifespan of those routinely exposed to 45°C, underscoring the need for precise temperature control.

In summary, marine battery thermal regulation demands a careful balance of conduction, liquid cooling, and phase-change materials, with distinct solutions for surface and submerged use. High-humidity conditions necessitate additional safeguards against thermal runaway, including advanced separators and real-time monitoring. The choice of cooling strategy depends on operational requirements, environmental constraints, and the tradeoffs between weight, complexity, and reliability. As marine electrification advances, continued innovation in thermal management will be essential to meet the rigorous demands of maritime applications.