INTRODUCTION
As International Maritime Organization (IMO) regulations continue to evolve, driving the shipping industry toward reduced emissions, industry leaders are increasingly evaluating hybrid and all-electric systems for their potential to help meet compliance targets. Among the myriad technologies shaping the future of marine and offshore operations, battery technology stands out as a potentially transformative solution. Researchers and developers are working on a range of efficient and sustainable battery technologies capable of delivering the required power without compromising the safety of personnel and assets.
Beyond reducing emissions, advanced battery technologies also have the potential to support the adoption of alternative fuels by improving efficiency and reducing fuel costs. For example, peak-shaving in hybrid systems can optimize engine loading and enhance efficiency.
This publication examines the latest advancements in rechargeable battery technology, including lithium-ion (Li-ion) and six next-generation batteries, from different perspectives. It begins by comparing the working mechanisms and technological maturity of different battery types. This study also explores the benefits and challenges of current and emerging energy storage systems for marine and offshore applications.
The initial evaluation indicates that most next-generation batteries require further technological advancements for widespread adoption. In addition to enhancing battery design, the industry needs to develop effective strategies for fire prevention, mitigation and rapid response to support safe operations. This study examines the severity of battery fires from two perspectives: thermal runaway (TR) and gas emissions.
Thermal runaway characteristics depend highly on battery chemistry, state of charge (SoC) and capacity. Consequently, the risks and consequences of battery fires are anticipated to increase significantly with the use of high-energydensity next-generation batteries. During TR, Li-ion batteries emit a mixture of gases, including flammable hydrogen and hydrocarbons, and highly toxic and corrosive gases like hydrogen fluoride (HF) and carbon monoxide (CO). Next-generation batteries pose additional risks, releasing gases such as silicon tetrafluoride (SiF₄) from silicon anode batteries and hydrogen sulfide (H₂S) from lithium-sulfur (Li-S) batteries.
CURRENT TECHNOLOGIES
A rechargeable (secondary) battery is an electrochemical device consisting of two electrodes that are isolated by a separator and soaked in electrolyte to promote the movement of ions, storing chemical energy and releasing electrical energy [1]. Their ability to be recharged and reused multiple times makes them a sustainable and economical energy solution. Secondary batteries are available in a variety of chemistries, including Li-ion, nickel-cadmium (NiCd), nickelmetal hydride (NiMH) and lead-acid. They are becoming increasingly essential in the marine industry by powering a wide range of systems. Batteries, specifically Li-ion, are widely used in portable electronic devices. They can also serve as the main source of power for all-electric vessels and can be installed in hybrid vessels to support both propulsion and auxiliary systems.
BATTERY APPLICATIONS
Batteries offer tangible benefits in marine operations, supporting advancements in efficiency, regulatory compliance and emission reduction in key areas, including:
• Zero-emission applications enable ships to operate with full or partial battery-electric propulsion. This can include cold ironing, which is where ships connect to shore power while docked to eliminate local emissions, contributing to environmental benefits and improved air quality in port areas.
• Hybrid applications optimize the use of traditional engines or fuel cells, leading to reduced fuel consumption, emissions and operational costs. Batteries function as a “spinning reserve” for redundancy safety, facilitate load leveling and enable cyclic operations for greater efficiency.
• Dynamic applications utilize batteries for immediate and backup power needs, enhancing safety and enabling dynamic load transitions and peak shaving for optimized efficiency.
• Energy harvest applications allow batteries to store energy from onboard or shore-based systems, promoting operational efficiency and sustainability. The harvested energy can be utilized for various purposes, including powering cranes or onboard systems.
LITHIUM-ION BATTERY
Lithium-ion batteries are gradually replacing lead-acid, NiCd and NiMH batteries as the leading energy storage technology for maritime applications. Lithium-ion batteries feature superior energy density, low self-discharge rate, and cycle life for electrical energy systems and distribution on vessels (see Figure 2 and Table 1).
Despite their advantages, safety concerns remain the biggest challenge for Li-ion batteries. To maintain safe operations in marine and offshore environments, complex battery management systems (BMS) are needed to monitor and control their operating ranges for voltage, current, temperature, SoC, state of health and more. Moreover, Li-ion batteries use flammable organic electrolytes, making them prone to fire or explosion during TR.
Thermal runaway is a condition where an internal or external factor triggers a self-sustaining chemical reaction, raising the temperature uncontrollably and potentially leading to battery failure and fires. These factors include thermal abuse (e.g., heating), electrical abuse (e.g., overcharging), and mechanical abuse (e.g., punctures causing internal short circuits). Other factors, such as degradation due to dendrite formation, internal short circuits (due to poor design), toxic and flammable gas generation and the propagation of TR between cells and modules, pose a risk to the safe usage of Li-ion batteries.
Internal protection devices, chemistries less prone to TR, insulation/cooling methods, battery management, control, monitoring and fire protection systems are essential to mitigate risks associated with the use of Li-ion batteries.
Table 1: Characteristics of
Lithium Cobalt Oxide(LiCoO2) – LCO
Lithium Manganese Oxide (LiMn2O4) – LMO
Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) – NMC
Lithium Iron Phosphate (LiFePO4) – LFP
Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) – NCA
Lithium Titanate (LiTiO3) – LTO
Figure 3: Materials have critical roles in battery performance [5].
Lithium-ion battery technology includes diverse types such as Li-ion cobalt oxide, Li-ion manganese oxide, Li-ion nickel manganese cobalt oxide, Li-ion nickel cobalt aluminum oxide, Li-ion iron phosphate and Li-ion titanate. Figure 3 provides the differences in characteristics between these Li-ion chemistries. The relative merit of various chemistries is provided with a value from one to five, with one representing the lowest level of performance and five representing the highest level of performance for individual characteristics.
Type
Composition
Lithium Cobalt Oxide (LCO): LiCoO 2 Cathode (~60% Cobalt), Graphite Anode
Lithium Manganese Oxide (LMO): LiMn 2 O4 Cathode, Graphite Anode
Lithium Nickel Manganese Cobalt (NMC) Oxide: LiNiMnCoO 2 , Cathode, Graphite Anode
Lithium Iron Phosphate (LFP): LiFePO4 Cathode, Graphite Anode
Lithium Nickel Cobalt Aluminum (NCA) Oxide: LiNiCoAlO 2 Cathode (~9% Cobalt), Graphite Anode
Lithium Titanate (LTO) Oxide: Cathode Lithium Manganese Oxide or NMC; Li 2TiO 3 (Titanate) Anode
Charge (C-rate)
• 0 7–1C, charge current above 1C shortens battery life
• 0 7–1C, 3C maximum
• 0 7–1C, charge current above 1C shortens battery life
• 1C typical, 3h charge time typical
• 0 .7C, 3h charge typical, fast charge possible with some cells
Table 2: Detailed characteristics of current Li-ion battery chemistries [5].
(Continued on next page)
• 1C typical
• 5C maximum
Discharge (C-rate)
Thermal Runaway
• 1C; 2 50 V cutoff
• Discharge current above 1C shortens battery life
cycles
• 150° C (302° F)
• Full charge promotes thermal runaway
• 1C
• 10C possible with some cells, 30C pulse (5s)
• 1C
• 2C is possible on some cells
• 1C
• 25C on some cells
• 40A pulse (2s)
Comments
• Very high specific energy
• Limited specific power
• Cobalt is expensive
• Market share has stabilized
• 250° C (482° F) typical
• High charge promotes thermal runaway
• High power but less capacity
• Safer than Li-cobalt
• Commonly mixed with NMC to improve performance
• Less relevant now; limited growth potential
• 210° C (410° F) typical
• High charge promotes thermal runaway
• Provides high capacity and high power
• Serves as a hybrid cell
• Market share is increasing
• Leading system; dominant cathode chemistry
• 270° C (518° F)
• Lower risk of thermal runaway, even if fully charged
• Flat voltage discharge curve but low capacity
• One of the safest Li-ions
• Elevated self-discharge
• Used primarily for energy storage
• •Moderate growth
• 1C is typical
• High discharge rate shortens battery life
• 10C possible
• 30C 5s pulse
• 150° C (302° F) typical
• High charge promotes thermal runaway
• One of the batteries with the lowest risk of thermal runaway
• Long life, fast charge
• Shares similarities with Li-cobalt
Table 2: Detailed characteristics of current Li-ion battery chemistries [5].
LITHIUM-ION BATTERY OUTLOOK FOR MARINE APPLICATION
• Good temperature tolerance (-30°–60° C), but low specific energy and expensive
• Among the safest Li-ion batteries
• Ability to ultra-fast charge
Lithium-ion batteries have demonstrated their effectiveness and reliability in powering all-electric and hybrid vessels, from small harbor crafts like tugboats to electric ferries. Several companies and organizations have successfully implemented Li-ion battery systems in marine applications. A technology readiness level (TRL) of 8–9 for the Li-ion battery technology for hybrid and all-electric vessels is relatively high, indicating that the technology is sufficiently mature for regular commercial use [6].
The deployment of battery vessels (hybrid and all-electric) is rapidly expanding. ABS classes many hybrid vessels with all-electric modes that can be entirely propelled by battery power and carry the ESS-LiBATTERY notation [1]. However, the onshore charging infrastructure should be carefully planned to meet the operational needs of fully electric vessels. The amount of onboard storage required may be dictated by the availability of the local charging infrastructure.
3 TRL: Technology readiness level is a method used to assess the maturity of a particular technology. It provides a consistent point of reference for evaluating how developed a technology is, ranging from basic principles to fully operational systems. TRLs are measured on a scale from 1 to 9, with 1 being the least mature and 9 being the most mature.
Spining Reserve
Backup power to running generators
Benefits include:
• Improved Safety
• Reduced fuel consumption and engine maintenance
Enhanced Ride Through
Short time backup power to running generators
Benefits include:
• Improved Safety
• Reduced fuel consumption and engine maintenance
Peak Savings Level power seen by engines and o set need to start new engines
Benefits include:
• Reduced fuel consumption and engine maintenance
Strategic Loading
ESS used to charge or discharge with the aim of optimizing engine operating point
Benefits include:
• Reduced fuel consumption
Enhanced Dynamic Performance Instant power in support of running engines
Benefits include:
• Reduced fuel consumption
• Enable for “slower” sources like LNG and Fuel Cells
Zero Emission Operation
Power system is fully powered by ESS
Benefits include:
• Quiet engine room
• Zero emission operation
In addition to the different applications discussed in section 2.1, Li-ion batteries offer several additional advantages, including reduced emissions since they do not produce any direct emissions during normal operation. This makes their environmental impact lower than that of conventional power sources like fossil fuels (see Figure 4). However, it is important to consider the full life cycle of these batteries to understand their environmental impact.
Lithium-ion also provides improved performance and lower operating costs, offering a consistent and reliable power source that enhances vessel performance. Although initially more expensive than traditional internal combustion type engines, they have lower operating costs because they do not require expensive fuel, have fewer moving parts and require less maintenance. The costs of Li-ion batteries have been decreasing over the last decade and are expected to continue decreasing as the price of their raw materials becomes less of a barrier. However, shoreside infrastructure and power electronics needed for battery charging remain significant cost drivers for future projects.
Additionally, there are several regulations and standards governing the use of Li-ion batteries in marine applications. The batteries pass through various safety tests like overcharge, forced discharge, high charging rate, external short circuit, impact, thermal abuse, altitude simulation and vibration following the necessary codes and standards (e.g., International Electrotechnical Commission (IEC) 62619, IEC 62620, UL 1973, UL 9540, UL 9540A and GB 38031). Also, class societies like ABS have developed specific Rules for the use of Li-ion batteries for marine and offshore applications, covering aspects such as battery design, installation and testing [1].
CHALLENGES AND LIMITATIONS OF LI-ION BATTERIES
Research indicates that Li-ion batteries are nearing their theoretical limits in energy and power density, which can create space and weight challenges for larger battery systems needed to meet higher electrical load requirements, such as the electrical energy needed for ocean-going vessels (Figure 5). Therefore, the stability and maneuverability of a vessel should be evaluated, particularly considering the weight of a large battery system.
Furthermore, the manufacturing and disposal processes associated with Li-ion batteries can produce indirect emissions that impact the environment as well as pose health and safety risks. The manufacturing process involves the extraction, processing and transportation of raw materials such as lithium, cobalt, nickel and other metals, which can result in greenhouse gas (GHG) emissions, air pollution and water pollution. According to a study by the Swedish Environmental Research Institute, the production of a typical Li-ion battery with a capacity of 20 kilowatt-hour (kWh) can result in GHG emissions of between 61 and 106 kilograms (kg) of carbon dioxide (CO2) equivalent per kWh of capacity, meaning the total GHG emissions during the fabrication process of a 20 kWh Li-ion battery can range from 1.22 to 2.12 metric tons of CO2 equivalent [8]. Additionally, the transportation of raw materials and finished products can result in emissions from fossil fuel-powered vehicles.
If not properly disposed of, Li-ion batteries can release toxic substances such as heavy metals, contaminating soil, water and air. The recycling process for Li-ion batteries can be energy-intensive and produce emissions if not done correctly. Overall, while Li-ion batteries for marine applications do not produce direct emissions during operation, their indirect emissions from the manufacturing and disposal processes should be considered to understand their full environmental impact.
Given these considerations, the importance of recycling and repurposing batteries becomes clear. These processes can provide significant benefits, including alternative uses for onshore applications, waste reduction and the recovery of valuable materials. This makes battery recycling and repurposing a promising area for further research and development. However, there are challenges to overcome, such as the economic feasibility of the process, since the costs of collecting, testing and repurposing batteries can be substantial.
Lithium-ion batteries can pose safety risks due to their chemical composition and the potential for TR, a chain reaction that can occur if a battery overheats, causing it to release heat and potentially ignite nearby materials. This can happen if the battery is damaged, overcharged or exposed to elevated temperatures, leading to a fire or explosion that can be dangerous and difficult to control. Mitigating the fire safety concerns requires complex monitoring systems to keep the Li-ion battery within the proper operating range for temperature and voltage.
Offshore charging infrastructure for batteries is still in the preliminary stages of development, meaning vessels may need to return to shore frequently for charging, limiting their operating range.
The upfront cost to install Li-ion batteries is higher than implementing traditional fuel-powered engines, posing an economic barrier for some vessel owners who may not have the financial resources to invest in a new power system. As of 2024, the estimated average cost to produce 1 kWh of energy from Li-ion batteries per module is around $115 [9].
For instance, reducing or eliminating emissions for an entire fleet of tugboats will necessitate retrofitting, as a tugboat’s lifespan can surpass 30 years. This poses challenges for hybrid and all-electric technologies, as retrofitting existing conventional vessels to hybrid or full battery power is challenging.
Alongside the difficulties in selecting the best battery chemistry for a vessel’s operational profile and the limited market options, batteries have a limited lifespan and will need to be replaced periodically. Replacements can be expensive and impact the vessel’s long-term operating costs. Therefore, it is crucial to evaluate these factors thoroughly when planning a Li-ion battery retrofit or newbuild.
EMERGING LI-ION BATTERY TECHNOLOGIES
The limitations of the current Li-ion battery technology have heightened the focus on the research, development and commercialization of next-generation batteries.
This study explores the technological advancements of emerging Li-ion batteries, including silicon anode, Li-S and lithium metal, assessing their potential for application in the maritime industry.
SILICON ANODE
Silicon anode cells, with their ultra-high energy density, are among the most promising candidates for commercial use in the next generation of batteries. Silicon anodes have a theoretical specific capacity of approximately 3,600 milliampere-hours per gram (mAh/g), almost 10 times higher than a commercial Li-ion battery with graphite anodes (~350 mAh/g). Silicon anode cells are categorized under the Li-ion battery family due to their similar operating principles to those of commercial Li-ion batteries. A silicon anode replaces the graphite anode of Li-ion battery while the cathode remains the same material (e.g., nickel manganese cobalt [NMC], lithium iron phosphate [LFP], lithium cobalt oxide [LCO]). The electrolyte components include conventional alkyl carbonates (e.g., ethyl carbonate, dimethyl carbonate, etc.) and lithium salt (LiPF6). Furthermore, the electrolyte can be topped with additives like lithium bis(trifluoromethanesulfonic)imide (LiTFSI), lithium perchlorate and fluoroethylene carbonate (FEC) to improve the stability of the solid electrolyte interface (SEI).
In addition, silicon’s abundant availability and environmentally friendly nature make it a potential material for largescale manufacturing of high-energy-density silicon anode cells.
To commercialize silicon anode cells for large-scale and marine applications, several challenges need to be addressed. During the lithiation and delithiation process , silicon anodes typically undergo significant volume changes (300–400 percent), which can cause the active materials to break down, leading to uncontrolled SEI growth and battery degradation. Researchers are actively investigating these issues and implementing various modifications to make silicon anode cells viable for commercial use.
Commercial products with silicon anodes are available and can achieve high energy densities of 300–400 Wh/kg [10]. However, they are often very expensive due to the complex manufacturing process. To address some of the challenges associated with silicon anodes, battery manufacturers commonly use a silicon/carbon composite, incorporating 10–50 percent silicon. This approach helps mitigate some difficulties while still improving energy density to around 300 Wh/kg.
LITHIUM-SULFUR BATTERIES
Lithium-sulfur batteries have significant potential for the next generation of energy storage systems due to their high theoretical energy density (2,600 Wh/kg) and specific capacity of sulfur cathodes (1,675 mAh/g). They are expected to achieve practical energy densities several times higher than current Li-ion batteries.
However, despite their potential, Li-S batteries face significant operational challenges and safety concerns, which have hindered their widespread commercialization.
Several inherent issues impede the practical use of Li-S batteries:
• The “shuttling effect” caused by soluble lithium polysulfides during cycling, leading to low coulombic efficiency and loss of active materials.
• The complex phase transition from octasulfur (S8) to lithium polysulfides (Li2 S2/Li2 S) and the insulating nature of these compounds result in slow kinetics and high reduction and oxidation (redox) overpotential.
• Uneven deposition of metallic lithium dendrites on the anode surface, forming an unstable SEI film during charging and discharging, poses safety risks. Additionally, these dendrites can break lithium crystals, creating “dead Li” (Figure 6) that reduces long-term cycling efficiency.
Current research focuses on developing safe electrolytes to form stable SEI layers and prevent gas generation, designing separators to suppress dendrite formation and reduce chemical crosstalk, and modifying electrodes to enhance stability.
Lithium-sulfur battery prototypes demonstrated energy density greater than 400 Wh/kg, showing their promise. However, due to the above mentioned limitations, the cycle life is typically short.
LITHIUM METAL BATTERIES
Lithium metal, with its low density of 0.59 grams per cubic centimeter (g/cm³), boasts an exceptionally high theoretical specific capacity of 3,860 mAh/g as an anode, making it a highly researched material for rechargeable lithium metal batteries. Figure 6 illustrates the schematic of lithium metal batteries and highlights the challenges for large-scale applications.
Lithium metal batteries utilize pure lithium metal as the anode, paired with various cathode materials such as LFP, Li-S, NMC, LCO and manganese dioxide (MnO2). The electrolyte composition is tailored to the chosen cathode material. For instance, lithium perchlorate in propylene perchlorate and dimethoxy ethane are used for MnO 2 cathodes. Two primary obstacles hinder the widespread adoption of lithium metal batteries: dendrite growth during charge and discharge cycles, and low coulombic efficiency during operation. Dendrite formation poses safety risks due to internal short circuits and reduces the cycle life of lithium metal batteries. While using excess lithium metal can mitigate low coulombic efficiency, it also accelerates dendrite formation, leading to potential failures and fires.
ADVANCED CATHODE MATERIALS
As the development of Li-ion batteries continues, new cathode chemistries are also being continuously developed. Two recent additions to Li-ion battery chemistry worth mentioning are lithium manganese iron phosphate (LMFP) and lithium manganese-rich (LMR) cathodes.
Lithium manganese iron phosphate is a modified LFP material with some iron ions replaced by manganese ions. The higher stability of Mn 2+/3+ redox chemistry allows higher oxidation potential, bringing its voltage platform to 4.1 volts (V), on par with NMC chemistry (4.3 V), while still maintaining the thermal stability of LFP. The downside of LMFP is the tendency of manganese ions to distort the lattice. At the cell level, it manifests low power performances and reduced cycle life, like LFP Li-ion batteries [11].
Lithium manganese-rich, for example Li1.2Mn 0.6 Ni0.2O2 , is in fact a mixture of lithium nickel oxide and LMO, which offers a high specific capacity (greater than 250 mAh/g compared to 190mAh/g of NMC) and a high voltage (4.5–4.7 V compared to Li-ion, and 4.3 V of NMC). With an LMR cathode, the energy density of the Li-ion battery cell can be significantly boosted. Its downside is stability, as it shares the instability of layered oxides and manganese redox chemistry. At the cell level, the outcome is thermal stability comparable with NMC Li-ion batteries, which require careful battery management [12].
BEYOND LITHIUM-ION
Extensive research efforts in new energy storage solutions have contributed to implementing battery storage technology in marine applications. Several promising battery technologies are being researched, including redox flow, sodium-ion (Na-ion) batteries and solid-state batteries. Sodium-ion batteries tackle the high costs and resource constraints of Li-ion batteries by using readily available materials. Meanwhile, safety issues associated with the use of organic liquid electrolytes are addressed using solid-state batteries with solid electrolytes. Although these advanced batteries are promising for maritime transportation and offshore energy storage, their safety aspects are still not fully explored.
SOLID-STATE BATTERIES
Solid-state batteries use a solid electrolyte instead of the liquid or gel electrolytes found in conventional Li-ion batteries. They present a promising solution for overcoming existing challenges by employing nonflammable and electrochemically stable solid electrolytes, including polymers, ceramic and polymer-inorganic composites [13]. These batteries use the same anode and cathode materials as Li-ion batteries, resulting in identical electrochemical reactions. Solid-state batteries offer an energy density of 500–800 Wh/kg.
One significant advantage of solid-state batteries is their improved safety, due to the non-flammable solid electrolyte that minimizes the risk of leaks and fires, making them safer than their liquid counterparts. They also have a longer cycle life, as they can endure more charge and discharge cycles, translating to a longer lifespan. Additionally, solidstate batteries can operate efficiently across a broader range of temperatures, making them suitable for various applications [14]. However, the production of solid-state batteries is currently more expensive due to the complexity of materials and processes involved, and ensuring the stability and longevity of the materials used in these batteries remains a significant challenge.
When it comes to regulations, there are no universally recognized, distinct industry-wide design standards specifically for solid-state batteries. However, several established standards offer guidelines and testing protocols to ensure the safety, reliability and performance of these batteries. These standards, originally developed for conventional Li-ion batteries, are also applicable to solid-state batteries. The standards assess various aspects such as electrical performance, thermal stability, mechanical integrity and safety under diverse conditions.
POLYMER SOLID-STATE BATTERIES
The most mature solid-state battery technologies use solid polymer electrolytes (SPE): a lithium metal negative electrode and a metal oxide cathode combined with lithium salt and polymer to form a plastic composite. Polymeric solid electrolytes like polyacrylonitrile (PAN), polyvinyl chloride (PVC), and polyethylene oxide (PEO) are being researched. To be activated, SPE-type solid-state batteries must be heated to 140°-176° F (60°-80° C).
Given the limitations of polymer solid electrolyte — low ionic conductivity at room temperature — a small amount of liquid electrolytes, termed “semi-solid” or “gel electrolyte,” is added to polymer solid-state batteries. Adding liquid electrolytes helps improve performance, sometimes significantly, but it does not completely address its flammability. Some of the liquids may be trapped in the polymer matrix, which reduces the risks, but more tests should be conducted to fully evaluate the safety performance.
CERAMIC AND SULFIDE-BASED SOLID-STATE BATTERIES
Ceramic and sulfide-based solid-state batteries represent a promising advancement in energy storage technology. These batteries utilize solid electrolytes, offering a safer alternative to the flammable liquid electrolytes used in conventional Li-ion batteries. Ceramic and sulfide-based solid electrolytes are particularly notable for their high ionic conductivity and robust mechanical properties, making them ideal for solid-state battery applications.
Despite their potential, there are still challenges to overcome, particularly regarding interfacial stability and manufacturing processes.
Current research is exploring various ceramic and sulfides solid electrolytes such as lithium germanium phosphorous sulfide (Li10 GeP2 S12 , LGPS), lithium lanthanum zirconium tantalum oxide (Li6.4La 3Zr1.4Ta0.6 O12 , LLZTO) and lithium lanthanum zirconium niobium oxide (Li6.75La 3Zr1.75Nb 0.25O12 , LLZNO). Notably, the thermal stability of solid electrolytes can reach up to 1,000° C for lithium lanthanum zirconium oxide (Li7 La 3Zr2O12 , LLZO), making it less prone to TR.
SOLID-STATE BATTERIES OUTLOOK
The future of solid-state batteries in marine applications looks promising, with ongoing research and development expected to overcome current challenges and unlock their full potential. The transition to mass production of solidstate batteries is anticipated to occur after 2030, driven by advancements in materials science, manufacturing processes and economies of scale. As these batteries become more commercially viable, they are expected to play a crucial role in the maritime industry’s transition to more efficient energy storage solutions.
In summary, solid-state batteries offer a compelling combination of safety, energy density, durability and environmental benefits, making them a promising technology for the future of marine applications. With continued innovation and investment, solid-state batteries are poised to revolutionize energy storage in the maritime sector.
SODIUM BATTERIES
Sodium batteries are emerging as a promising alternative to traditional lithium-based energy storage systems, offering potential advantages in cost, resource availability and safety. Two key types of sodium-based batteries are gaining attention: high-temperature sodium batteries, which operate at elevated temperatures, and Na-ion batteries, which function at room temperature and are structurally similar to Li-ion batteries but use more abundant and less expensive sodium.
HIGH-TEMPERATURE SODIUM BATTERIES
High-temperature sodium batteries, also known as sodium beta or molten salt batteries, are hermetically sealed batteries featuring metallic sodium as the negative electrode and ceramic beta-alumina as the electrolyte. These batteries function at elevated temperatures ranging from 500–698° F (260–370° C), keeping the active materials molten and maintaining ionic conductivity. There are two main types of commercially available high-temperature sodium batteries: sodium sulfur and sodium nickel chloride. Sodium sulfur batteries consist of a sodium negative electrode, beta-alumina electrolyte, and sulfur positive electrode, operating within a temperature range of 590–698° F (310–370° C). On the other hand, sodium nickel chloride batteries feature a sodium negative electrode, beta-alumina electrolyte, and a positive electrode that can be composed of nickel, nickel chloride or sodium chloride, with an operating temperature range of 500–662° F (260–350° C) [15].
These batteries offer an energy density ranging of 90–120 Wh/kg, making them suitable for applications requiring significant power output, and they operate efficiently at elevated temperatures, enabling stable performance in extreme conditions. However, they require high operating temperatures (500–698° F) for optimal performance, which can be energy-intensive and may necessitate specialized equipment, including heaters or furnaces, thermal insulation, heat-resistant materials and robust encapsulation. Additionally, the production and maintenance of these batteries can be costly due to the materials and technology involved. The long-term stability of the materials used also remains a challenge.
High-temperature sodium batteries are rigorously evaluated for performance, safety and reliability, making them suitable for diverse applications, including marine environments. The International Electrotechnical Commission (IEC) 62984 standard outlines the performance requirements and test procedures for high-temperature secondary batteries, including sodium-based batteries, used in mobile and stationary applications. This standard encompasses sodiumbased batteries, such as sodium sulfur and sodium nickel chloride batteries, and whose nominal voltage does not exceed 1,500 V.
For instance, ABS has recently granted sodium metal chloride batteries a new technology qualification. The cathode of this battery is composed of metals, primarily nickel and table salt (NaCl), while the anode consists of molten sodium. The anode and cathode are separated by a solid electrolyte made of sodium beta-alumina, a ceramic material that facilitates fast transport of sodium ions at temperatures above 200° C.
This certification confirms that the batteries meet the rigorous standards necessary for the next stage of development, which involves system integration. This step is essential for their future use in the marine and offshore industries, which are increasingly seeking sustainable and reliable energy solutions.
SODIUM-ION BATTERIES
Sodium-ion batteries use sodium ions to store and release energy, similar to how Li-ion batteries use lithium ions. They operate through a liquid electrolyte that facilitates the movement of sodium ions between the anode and cathode during charging and discharging.
As Li-ion battery technology continues to advance, researchers and environmental advocates are increasingly raising concerns about sustainability due to the limited availability of lithium. Sodium, on the other hand, is widely available [16]. Sodium-ion battery technology offers tremendous potential to be a counterpart to Li-ion batteries. However, despite the similarities in electro-chemistry between Na-ion and Li-ion batteries, there are remarkable differences in the physicochemical properties between sodium and lithium that give rise to different behaviors [17].
The cathode materials often used are sodium layered transition metal oxides while the anode materials can include hard carbon or graphite. Na-ion batteries typically have an energy density ranging from 75–200 Wh/kg. This range is similar to that of LFP but lower than the energy density of other types of Li-ion batteries. They offer thousands of charge-discharge cycles, making them durable for long-term use, and the nominal cell voltage is around 3.0–3.1 V. Companies worldwide have been working to develop commercially viable Na-ion batteries. For instance, a 100 megawatt-hour grid battery was installed in China in 2024 for land-based applications [18].
Thanks to their numerous inherent advantages, Na-ion batteries are a promising technology for marine applications. The widespread availability and lower sodium cost make Na-ion batteries appealing for large-scale energy storage solutions needed in marine environments. These batteries can be seamlessly integrated with renewable energy sources such as solar and wind power, offering marine vessels a sustainable energy storage option and helping meet regulatory compliance. Current research is dedicated to enhancing the energy density, cycle life and overall performance of Na-ion batteries. Advances in materials science and battery design are expected to address existing challenges and fully realize the potential of Na-ion batteries for marine applications.
In summary, Na-ion batteries have significant potential as an alternative to traditional Li-ion batteries thanks to their cost-effectiveness, safety benefits and limited environmental impact.
AQUEOUS SODIUM-ION BATTERIES
Aqueous Na-ion batteries, which are also referred to as saltwater batteries, consist of a manganese oxide positive electrode, a carbon titanium phosphate composite anode, a saltwater solution electrolyte, and sodium ions that intercalate between the positive and negative electrode during the charge and discharge operation. These sodium batteries operate at ambient temperatures with an optimal range of 23–104° F (–5–40° C).
Aqueous Na-ion batteries are less popular than other types due to several key challenges. One major issue is their lower energy density, which limits their ability to efficiently store and deliver power. Due to these technical hurdles and the focus on improving the more promising solid-state and non-aqueous Na-ion batteries, the development and commercialization of aqueous Na-ion batteries have lagged behind other types.
FLOW BATTERIES
Redox flow batteries (RFBs) operate based on a chemical redox reaction between two liquid electrolytes within the battery cell. These electrolytes are stored in separate tanks and pumped into the cell as required, where they react across an ion-selective membrane, preventing them from mixing. The electrolytes, known as redox pairs, can reversibly react with each other to charge and discharge the battery as needed.
Redox flow batteries come in several types, each with unique characteristics and applications, including:
• Vanadium redox flow batteries (VRFBs)
• Zinc-bromine (Zn-Br) flow batteries
• Iron-chromium (Fe-Cr) flow batteries
• Hydrogen-bromine (H-Br) flow batteries
• Organic redox flow batteries
Table 3: Example chemistries of flow batteries [20].
Zinc bromine and VRFB are two types of flow battery technologies currently available on the market. Zinc-bromine flow batteries have zinc at the negative electrode and bromide at the positive electrode with an aqueous solution containing zinc-bromide and other compounds contained in reservoirs. During charging, energy is stored as a zinc metal within the cell and polybromide in the cathode reservoir. During discharge, the zinc is oxidized to zinc oxide and the bromine is reduced to bromide. Vanadium redox flow batteries contain vanadium salts in various stages of oxidation in a sulfuric acid electrolyte. Charging and discharging the battery changes the oxidation state of the vanadium in the electrolyte solutions.
One significant challenge of implementing RFB technology in maritime applications is its low energy density. The substantial space required for these systems can be problematic for marine vessels where space and weight are critical factors. However, ongoing research aims to enhance electrolytes and improve energy density, potentially mitigating this concern.
Redox flow batteries should be designed in accordance with recognized industry standards such as the IEC 62932 series. These standards cover various aspects of flow battery design, performance and safety, ensuring that the systems are dependable and meet industry requirements.
• Highly volatile prices of minerals (i e , the cost of VRFB energy)
• Relatively poor efficiency (compared to Li-ion batteries) Heavy weight of the system, especially the electrolyte
• Relatively poor energy-tovolume ratio compared to standard storage batteries
• Moving parts in the pumps produce the flow of electrolyte solution
• Toxicity of compounds .
• Marine/offshore environmental conditions (Inclination, structural integrity, risk of electrolyte leakage)
Table 4: Characteristics of most common redox flow batteries.
BATTERY
SPECIFIC ENERGY DENSITY (WH/KG)
Figure 10: Specific energy density range based on the recent development of various battery types.
Battery Type
Key Components
Anode: See Table 2
Cathode: See Table 2
Conventional Lithium-Ion
Electrolyte: Lithium salt (e g , LiPF6) and organic carbonates
solvent (e g , ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC)
Working Mechanism/ Salient Feature(s)
• Recharging involves supplying external electrical power to reverse the cell’s electrochemical reactions
• During discharge, lithium ions move from the anode to the cathode via the electrolyte While charging, the flow reverses
• Similar to Li-ion batteries, but with a silicon anode replacing graphite
Maritime Application
Silicon Anode
Metal
Solid-State
Anode: Silicon
Cathode: Same as Li-ion batteries
Electrolyte: Same as Li-ion batteries with additives
Anode: Lithium metal
Cathode: Sulfur
Electrolyte: Same as Li-ion batteries (e g LiTFSI with etherbased solvents like 1,3-dioxolane (DOL)/ dimethoxyethane (DME) mixtures)
• Silicon reacts with lithium to form a lithiumsilicon alloy (LixSi), causing significant volume expansion
• Forms an unstable passivation layer with the electrolyte; additives stabilize this layer
• Currently used in small quantities in graphiteanode batteries
• Similar to Li-ion batteries, but with a silicon anode replacing graphite
• Silicon reacts with lithium to form a lithiumsilicon alloy (LixSi), causing significant volume expansion
• Forms an unstable passivation layer with the electrolyte; additives stabilize this layer
• Currently used in small quantities in graphiteanode batteries
Anode: Lithium metal
Cathode: Metal oxides (e g , MnO2)
Electrolyte: Same as Li-ion batteries
Anode: Lithium metal
Cathode: Metal oxides, e g , MnO2
Electrolyte: Solid inorganic electrolytes (e g , LGPS)
• The anode is pure metal, unlike graphite in Li-ion batteries
• Dendrite formation is a major safety concern
• Zero-emission applications,
• Hybrid applications
• -Dynamic applications
• Energy harvest applications
• Refer to section 2 1
Technology Maturity
Commercialized (TRL: 8-9) [6]
Example of Industries Recognized Standard
• Solid-state batteries typically use organic or polymeric electrolytes, unlike the organic electrolytes used in Li-ion batteries
• Solid-state batteries have the potential to provide high energy density and a safer alternative to current Li-ion batteries, making them an alternative option for the same applications
Research prototype (TRL: 4-5) [22]
IEC 62619
IEC 62620
UL 1973
Prototype developed (TRL: 5-6) [23]
Research prototype (TRL: 4-5)
Research prototype (TRL: 4-5)
Table 5: Comparison of working mechanisms and technological maturity of different battery types. (Continued on next page)
IEC 62619
IEC 62620 UL 1973
HighTemperature Sodium
Sodium-Ion
Anode: Metallic
sodium
Cathode: ( e g , sulfur)
Electrolyte: ceramic beta-alumina
Working Mechanism/ Salient Feature(s)
• These batteries typically consist of a sodium metal anode, a ceramic beta-alumina solid electrolyte and a cathode made of materials like sulfur or nickel chloride
• During discharging, the sodium ions move back from the anode through the electrolyte to the cathode, where they react with the cathode material to produce electrical energy
• The high operating temperature ensures that the materials remain in a molten state, which is necessary for the ionic conductivity and overall stability of the battery
Anode: Carbonbased (e g , Graphite)
Cathode: e g , Sodium vanadium phosphate (NVP), sodium lithium manganese oxide (NLMO)
Electrolyte: Sodium salt (e g , sodium hexafluorophosphate (NFP), and organic carbonates solvent (e g , EMC, DMC)
• Similar to Li-ion batteries
• An unstable passivation layer forms on the anode side
These batteries can be integrated into hybrid marine power systems, working alongside other energy sources to optimize fuel efficiency and reduce emissions They can also serve as a reliable backup power source, helping keep critical systems operational
(TRL: 8-9)
Anode (Anolyte): e g , V2+/V3+
Cathode (Catholyte): e g , VO2+/ VO2+
Solvent: e g , Hydrochloric (HCl) and sulfuric (H2SO4)-based acidic solutions
Typically, a redox flow battery includes storage tanks and pumps For instance, vanadium in different oxidation states is dissolved into an acidic solvent to form a cathode (catholyte) and anode (anolyte) (liquid-based electrodes instead of solid)
The catholytes/anolytes are stored in tanks and pumped externally to a membrane, where the electrochemical reaction occurs
While Na-ion batteries are still in the early stages of their marine application, they show significant potential Their wide range of advantages, including cost-effectiveness, strong safety features, excellent temperature performance and environmental sustainability, makes them a compelling choice for marine battery use
Due to their low energy density, redox flow batteries require careful consideration of space and weight to determine their suitability for hybrid and dynamic applications in maritime environments However, they can be excellent candidates for energyharvesting applications where space and weight
Pilot scale production (TRL: 6-7)
IEC 62619
IEC 62620 UL 1973
Commercialized (TR: 8-9)
IEC 62932 UL 1973
Table 5: Comparison of working mechanisms and technological maturity of different battery types. (Continued from previous page)
