Role of second-life batteries in electrified marine propulsion systems

The electrification of marine propulsion systems represents a significant shift in maritime transportation, driven by increasing environmental regulations and sustainability goals. Within this transition, second-life batteries—those previously used in electric vehicles (EVs) that no longer meet the demanding requirements of automotive applications—have emerged as a promising resource. These batteries typically retain 70-80% of their original capacity when retired from EVs, making them potentially valuable assets for less demanding applications rather than immediate recycling.

The marine sector presents unique opportunities for battery repurposing due to its diverse power requirements and operational profiles. Vessels ranging from small pleasure craft to large commercial ships can potentially utilize second-life batteries for various functions, including propulsion, auxiliary power, and energy storage during port operations. This application domain has gained attention as maritime regulations increasingly restrict emissions in coastal waters and ports.

Historically, marine propulsion has relied heavily on diesel engines, contributing significantly to maritime emissions. The International Maritime Organization (IMO) has established ambitious targets to reduce greenhouse gas emissions from international shipping by at least 50% by 2050 compared to 2008 levels. This regulatory pressure has accelerated interest in alternative propulsion technologies, with battery-electric and hybrid systems gaining traction.

The technical evolution of marine battery systems has progressed from lead-acid to advanced lithium-ion chemistries, paralleling developments in the automotive sector. This technological alignment creates a natural pathway for repurposing EV batteries in marine applications. As the first generation of mass-market EVs reaches end-of-life, a substantial supply of second-life batteries is becoming available, coinciding with growing demand for electrified marine solutions.

The primary objectives of investigating second-life batteries for marine propulsion include: assessing technical feasibility across different vessel types and operational profiles; developing cost-effective integration strategies that address marine-specific challenges such as saltwater exposure and vibration; establishing safety protocols and certification pathways; and quantifying environmental benefits through lifecycle assessment. Additionally, there is significant interest in developing business models that can capture value across the battery lifecycle, from automotive to marine applications and eventually to recycling.

This research area sits at the intersection of circular economy principles, maritime decarbonization efforts, and energy storage innovation. By extending battery useful life through marine applications, the approach promises to improve resource efficiency while potentially reducing costs for vessel electrification—a critical factor in accelerating adoption of cleaner propulsion technologies in the traditionally conservative maritime industry.

The global market for second-life batteries in marine applications is experiencing significant growth, driven by the increasing electrification of maritime transport and the expanding availability of retired electric vehicle (EV) batteries. Current market valuations estimate the second-life battery sector at approximately $2.3 billion in 2023, with marine applications representing around 15% of this market. Industry forecasts project a compound annual growth rate (CAGR) of 23-25% through 2030, potentially reaching $8.7 billion, with marine propulsion applications expected to capture an increasing share.

The demand for second-life batteries in marine propulsion systems is primarily concentrated in regions with established maritime industries and progressive environmental regulations. Europe leads this market segment, accounting for roughly 40% of global demand, followed by North America (25%) and Asia-Pacific (20%). Scandinavian countries, particularly Norway and Denmark, have emerged as early adopters due to their stringent emission regulations and well-developed maritime sectors.

Market segmentation reveals distinct customer profiles: commercial vessel operators seeking cost-effective electrification solutions represent approximately 45% of the market; ferry and passenger vessel operators focused on sustainability and public image account for 30%; and specialized marine applications such as port equipment and small recreational vessels constitute the remaining 25%. The price sensitivity varies significantly across these segments, with commercial operators being most cost-conscious.

Key market drivers include increasingly stringent maritime emission regulations, particularly in Emission Control Areas (ECAs) established by the International Maritime Organization (IMO). The 2020 global sulfur cap and upcoming carbon intensity regulations are accelerating the transition to electric and hybrid propulsion systems. Additionally, the growing price disparity between second-life batteries ($70-120/kWh) and new marine-grade batteries ($250-400/kWh) creates a compelling economic case for adoption.

Market barriers remain significant, including concerns about reliability in harsh marine environments, limited standardization across battery systems, and complex certification requirements. The fragmented nature of both the maritime industry and the second-life battery supply chain further complicates market development. Insurance and liability considerations also present challenges, with many underwriters requiring additional premiums for vessels using repurposed energy storage systems.

The competitive landscape features both established marine technology providers expanding into second-life applications and specialized startups focused exclusively on battery repurposing. Strategic partnerships between automotive manufacturers, battery recyclers, and marine system integrators are becoming increasingly common, creating new value chain configurations and business models centered around battery life-cycle management.

The repurposing of electric vehicle (EV) batteries for marine applications presents significant technical challenges that must be addressed to ensure safety, reliability, and performance. One primary challenge is the assessment of battery health and remaining useful life, as marine environments demand precise understanding of capacity degradation patterns. Current diagnostic methods often rely on simplified models that fail to account for the complex degradation mechanisms experienced in automotive applications, making accurate state-of-health determination difficult when transitioning to marine use.

Battery management systems (BMS) designed for automotive applications require substantial reconfiguration for marine environments. These systems must be adapted to handle different discharge profiles, thermal conditions, and safety parameters. The integration of multiple battery packs with varying degradation levels further complicates BMS design, requiring sophisticated balancing algorithms and monitoring capabilities beyond those needed in original applications.

Thermal management presents another critical challenge. Marine propulsion systems often experience more continuous high-power demands compared to the variable cycling of automotive applications. Second-life batteries with diminished thermal stability characteristics require redesigned cooling systems to prevent thermal runaway events, particularly challenging in the confined spaces of marine vessels where air or liquid cooling pathways may be limited.

Structural integrity concerns emerge when repurposing batteries for marine environments. Exposure to constant vibration, potential saltwater intrusion, and humidity creates corrosion risks not typically addressed in automotive battery designs. Protective enclosures must be engineered to withstand these conditions while maintaining accessibility for maintenance and monitoring.

Regulatory compliance represents a significant hurdle, as marine classification societies have established stringent safety standards that differ substantially from automotive regulations. Second-life batteries must meet these requirements despite their prior use history, often necessitating extensive testing and certification processes that add complexity and cost to repurposing efforts.

Standardization issues further complicate repurposing initiatives. The wide variety of EV battery architectures, chemistries, and form factors creates challenges in developing universal repurposing methodologies. This diversity necessitates customized engineering solutions for each battery type, limiting economies of scale and increasing technical complexity in integration projects.

Energy density limitations of degraded batteries may require larger battery installations to achieve equivalent performance to new systems, creating space utilization challenges aboard vessels where available volume is often at a premium. This spatial constraint can limit the practical application of second-life batteries in smaller marine vessels or those with specific design limitations.

The marine electrification market is currently in a growth phase, with second-life batteries emerging as a crucial component in sustainable marine propulsion systems. The global market is projected to expand significantly as maritime industries face increasing pressure to reduce emissions. Technologically, the sector shows varying maturity levels, with companies like Yamaha Motor, Toyota, and Honda leading in conventional marine propulsion adaptation, while battery specialists including CATL, Samsung SDI, and LG Energy Solution bring advanced energy storage expertise. Pure Watercraft and Volvo Penta are pioneering purpose-built electric marine solutions. Second-life battery implementation remains in early development stages, with automotive battery manufacturers like SK On and CATL exploring maritime applications as battery recycling infrastructure develops. The competitive landscape features cross-industry collaboration between traditional marine manufacturers and battery technology specialists.

The integration of second-life batteries into electrified marine propulsion systems represents a significant opportunity for enhancing environmental sustainability in maritime operations. These repurposed batteries, which have completed their primary lifecycle in electric vehicles but retain 70-80% of their original capacity, offer substantial environmental benefits compared to manufacturing new energy storage systems. Life cycle assessment studies indicate that repurposing EV batteries for marine applications can reduce carbon emissions by approximately 25-30% compared to new battery production, primarily by avoiding energy-intensive manufacturing processes and raw material extraction.

Marine environments are particularly sensitive to pollution, making the sustainable management of battery systems crucial. Second-life batteries extend the functional lifespan of lithium-ion cells by 5-10 years, significantly reducing waste generation and delaying final disposal challenges. This circular economy approach addresses critical resource constraints, particularly for materials like cobalt, lithium, and nickel, which face increasing demand pressure from the growing electrification trend across transportation sectors.

Water conservation represents another important environmental benefit. Traditional battery manufacturing requires approximately 7,000-9,000 liters of water per kWh of battery capacity produced. By extending battery lifecycles through marine applications, the water footprint per kWh of delivered energy over the battery's complete lifecycle is reduced by an estimated 40-45%.

The environmental impact assessment must also consider end-of-life management strategies. Marine applications of second-life batteries must incorporate robust monitoring systems to prevent potential leakage of electrolytes or thermal events that could harm marine ecosystems. Current research indicates that properly managed second-life battery systems can maintain safety standards comparable to new systems when equipped with appropriate battery management systems optimized for marine conditions.

From a sustainability perspective, the maritime industry's adoption of second-life batteries aligns with multiple United Nations Sustainable Development Goals, particularly SDG 12 (Responsible Consumption and Production), SDG 13 (Climate Action), and SDG 14 (Life Below Water). Quantitative sustainability metrics show that each megawatt-hour of second-life battery capacity deployed in marine applications potentially prevents 1.2-1.5 metric tons of CO2 equivalent emissions compared to conventional marine propulsion systems.

Regulatory frameworks are evolving to support this sustainability transition. The International Maritime Organization's strategy to reduce greenhouse gas emissions from ships by at least 50% by 2050 creates policy incentives for adopting electrified propulsion systems, with second-life batteries offering a cost-effective pathway to compliance while maximizing resource efficiency.

The regulatory landscape for maritime battery systems is evolving rapidly as the industry embraces electrification and second-life battery applications. International Maritime Organization (IMO) has established the International Convention for the Safety of Life at Sea (SOLAS) and the International Convention for the Prevention of Pollution from Ships (MARPOL), which indirectly impact battery systems through safety and environmental protection requirements. However, these frameworks were not specifically designed for electric propulsion systems, creating regulatory gaps.

Classification societies such as DNV GL, Lloyd's Register, and American Bureau of Shipping have developed more specific guidelines for maritime battery installations. DNV GL's class notation "Battery Power" and "Battery Safety" provide comprehensive requirements for design, installation, and operation of maritime battery systems. These standards address safety concerns including thermal runaway prevention, fire suppression systems, and battery management system requirements.

The International Electrotechnical Commission (IEC) has established IEC 62619 and IEC 62620 standards for secondary lithium cells and batteries for industrial applications, which are increasingly referenced in maritime regulations. Additionally, the International Association of Classification Societies (IACS) has been working on unified requirements for battery installations on vessels.

For second-life batteries specifically, regulatory frameworks remain underdeveloped. The European Union's Battery Directive (2006/66/EC) and its proposed revision address aspects of battery reuse but lack maritime-specific provisions. The absence of standardized testing protocols for determining the suitability of used automotive batteries for marine applications presents a significant regulatory challenge.

Port authorities and coastal states often impose additional requirements for vessels operating in their waters. For instance, Norway has established emission-free fjord regulations that indirectly promote battery-powered propulsion systems but do not specifically address second-life battery applications.

Liability and insurance frameworks for vessels utilizing second-life batteries remain ambiguous. Insurers typically require certification from recognized authorities, but the certification process for repurposed batteries lacks standardization. This regulatory uncertainty increases risk premiums for vessels employing second-life battery systems.

Emerging regulations are beginning to address end-of-life management for maritime batteries, with requirements for traceability, responsible disposal, and recycling. The Basel Convention on transboundary movements of hazardous wastes impacts international transportation of batteries for repurposing or disposal, adding complexity to global second-life battery supply chains in maritime applications.