Will Sodium-Ion Batteries Revolutionize Electric Ships?
April 27, 20262 hours
Christopher Arcus
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Advancements in sodium-ion batteries have come from a new generation of cells from CATL, BYD, and others, bringing the possibility of lower cells costs at higher volume in the near future. CATL has stated it expects oceanic electric ships to be possible in the next three years. Could $20/kWh Naxtra sodium-ion batteries help electric ships reach cost parity with diesel at oceanic distances in the near future? To find out, we need to know ship energy consumption and speed and adjust for expected battery performance in the next three years, the next Naxtra battery generation.
“Container ships increased their average speed by 1% compared to 2023, reaching 14.0 knots.”
Fuel consumption increases with the cube of speed. The data shows a 5,000 TEU Panamax container ship consumes about 50 tons of fuel per day at 17 knots. We can calculate results for this size ship crossing the Atlantic from Rotterdam to New York.
Rotterdam–to–New York Energy Consumption
The Rotterdam to New York sea route distance is 3,323 nm, which is 5,556 km. If a ship travels at 17 knots, it is going 19.56 mph, or 31.484 km/h. Over 5,556 km, it would take 176.5 hours, or 7.35 days, to cross the Atlantic to its destination (5,556 km/(31.484 km/hr)). With fuel consumption of 50 tons/day, a ship uses 367 tons of fuel per trip (50 t/day x 7.35 days). The lower calorific value of HFO is 39 MJ/kg.
1,000 kg = 1.102311 ton
1MJ = 0.27777 kWh
39 MJ/kg x 1,000 kg/1.1023 ton x 0.27777 kWh/MJ = 9,828 kWh/ton for HFO
With combustion efficiency of 0.5, that delivers 4,914 kWh/ton, or 4.914 MWh/ton, at the propeller shaft. For 367 tons of fuel, 367 tons x 4.914 MWh/ton = 1.803 GWh. With an electric motor efficiency of 0.9, the figure for energy storage required is 2.00 GWh for a 5,556 km route from Rotterdam to New York at 17 knots.
Battery Volume vs. Fuel Volume
A 5,000 TEU Panamax container ship can have 2 million gallons of fuel storage. 2 e 6 gal x 3.78 liter/gal x 0.001 cubic meter/liter = 7,560 cubic meters. For 33.1 m3 per TEU, this represents an equivalent of 7,560 cubic meter/[33.1 cubic meter/TEU] = 228 TEU Fuel Volume Equivalent.
If energy storage containers are 10 MWh/TEU, then it takes 200 TEU (2,000 MWh/10 MWh).
At 33.1 cubic meter/TEU, the volume will be 6,620 m3.
Containerized Battery Energy Storage (BESS) specification varies. Utility storage BESS standards differ from marine BESS, because they may be used for grid peak demand over short intervals less than one hour at high charge rates and require high cycle life. China is now using a 2 MWh marine TEU container standard not optimized for volume. Onshore BESS can be found in 5 MWh BESS 20 foot containers. Lithium utility storage BESS trade energy density for cost per kWh and cycle life. Land-based LFP utility storage must keep temperature in a narrow range near 30°C to attain 4,000 cycle life. LFP cells use thicker electrodes and lower energy density to optimize cost per kWh. Because utility storage BESS needs active cooling, it delivers less energy per TEU container. Thermal management consumes space and energy and increases weight. Sodium-ion BESS in ships can be passively cooled and densely packed. Calculations show Naxtra SIB cell volumetric energy density has increased and may match present day LFP, because it has a self-forming anode. Present day LFP is 434 Wh/l.
SIBs at $20/kWh are projected in about 3 years. By then, gravimetric energy density will improve from 175 Wh/kg to 200 Wh/kg, and by ratio, the volumetric energy density will be 484.6 Wh/l (200/175 x 434 Wh/l).
Ships do not need high cycle life. For 5,000 km distances, ships travel in about 8 days. Over a year, a 5,000 km range ship could cycle 40 times. Over a 25 year ship lifetime, that is only 1,000 cycles, easily met by most batteries, and greatly exceeded by sodium-ion battery 10,000 cycle lifetimes. For long trips, battery internal dissipation is miniscule. Losses are primarily motor electronics and control. Sodium-ion has a C of 5. Battery duration is 1 hr/5, or 12 minutes. Trip time is 176 hours. That is a discharge rate of 176 hours. Application duration/rated duration = 176/0.2 = 880. In this long duration electric ship example, current is 880 times less than battery rating. Battery internal resistance losses are decreased by current squared, giving negligible internal dissipation. Energy storage will be near ambient temperature with passive cooling. Together with greater temperature range and safety, sodium-ion requires little space for passive cooling.
Battery Electric Propulsion Volume Compared to Diesel
Given 484 Wh/l
2,000,000 kWh/ (0.484 kWh/l) = 4.132 e 6 litre
4.132 e 6 l x 1 e -3 cubic meter/l = 4,132 cubic meters
There are 33.1 cubic meters per 20 foot container (TEU)
4,132/33.1 = 125 TEU
Given 228 TEU fuel volume equivalent, there is a net theoretical decrease in required volume of 103 TEU required for sodium-ion. Max theoretical sodium-ion BESS TEU capacity is approximately 16 MWh. Sodium-ion can easily exceed 5 MWh/TEU with passive cooling.
2,000 MWh/(10 MWh/TEU) = 200 TEU
200 TEU x 33.1 m3 /TEU = 6,620 m3
The net volume using 10 MWh sodium-ion BES containers is -940 m3.
The equivalent TEU of fuel capacity depends on MWh/TEU. If 10 MWh/TEU, that gives 10 MWh/33.1 m3. The equivalent MWh for diesel fuel volume is 229 TEU. For 10 MWh/TEU and 2,000 MWh capacity, 200 TEU are needed. With 5 Wh/TEU, 400 TEU electric storage is needed, only 171 excess TEU, less than 3.5% of cargo volume. Present day sodium-ion volumetric energy density is good for about 400 Wh/l. That allows a theoretical maximum 13.24 MWh/TEU, good enough for a 10 MWh energy storage container. For LFP and near future Naxtra sodium-ion batteries with volumetric energy density over 400 Wh/l, electric ship energy storage is limited by TEU packing density, not cell volumetric energy density. In ship applications, volumetric benefits of passive cooling and low volatility are more important than cell energy density metrics.
- 10 MWh energy storage containers
- Motor and engine volume are low. Exhaust and cooling weight and volume differences are omitted. Electric motor efficiency is higher than diesel, resulting in lower cooling requirements.
Electric Motor vs Diesel Engine Weight
The weight of a marine diesel engine is 2,100 mt.
The weight of an electric motor is 150 mt.
The difference in motor weight is 1,950 mt.
Battery Weight vs Fuel Weight
2,000 e 6 kWh/0.200 Wh/kg = 10.0 e 6 kg = 10,000 mt batteries
Panamax ships carry 2 million gallons of fuel. Bunker fuel is 3.7 kg/gallon. 2 e 6 gallons x 3.7 kg/gallon = 7.4 e 6 kg = 7.4 e 3 mt = 7,400 mt. Fuel versus battery weight difference is 10,000 mt – 7,400 mt = 2,600 mt. Diesel versus electric motor weight difference is -1,950 mt. The sum of total weight differences is 2,600 mt – 1,950 mt = 650 mt. Electric propulsion is slightly heavier by 650 mt. Panamax ships weigh about 65,000 dwt. Loaded TEU containers weigh 24 mt. The excess weight is the equivalent of about 220 containers, under 5% of possible cargo TEU.
Opex Cost
Fuel Costs
Annual diesel fuel cost is computed from average global fuel cost for VLSFO (2025) at $570/metric ton. VLSFO is 11.28 kWh/kg, or 11,280 kWh/mt. At 48% efficiency, VLSFO delivers 5,400 kWh/mt. VLSFO costs $570/5,400 kWh = $10.56/kWh.
The US average industrial electricity rate was $0.084/kWh in 2025. Permanent Magnet Synchronous Machines (PMSG) for marine applications operate at 96% efficiency. Including efficiency, this translates to $0.0875/kWh stored. Global industrial electricity prices vary based on tax policies and legal matters, sometimes unrelated to wholesale prices. Swappable energy storage containers in combination with renewables can provide $0.084/kWh with renewable generation Power Purchase Agreements (PPA) for solar and wind at high utilization rates. A combination of existing generation and new renewables can provide electricity for swappable energy storage containers.
Traveling 7.5 days, and in port 1.5 days to unload all year, gives a 9 day cycle and 365/9 = 40.55 trips per year. 40 trips/year x 2.0 e 6 kWh/trip x $ 0.1056 – 0.0875/kWh = $1.448 e 6/year electricity cost difference.
Maintenance Cost
The annual maintenance cost for lubricants, filters, monitoring, personnel, and overhauls is about $1 million a year for a 5,000 TEU Panamax ship. Electric maintenance cost is nearly zero. The total opex cost difference is $2.5 million/year.
Capex
A 40,000 HP diesel costs $20–30 million. An electric drivetrain costs about $100,000 per MW, and 40,000 hp is 30 MW. 30 MW x $ 0.1 million/MW = $3 million. Electric motors and batteries have a longer life than marine diesels. Electric generators can last a century or more with little maintenance. The first generators at Niagara Falls are still in working order 100 years later. 2,000 MWh x $20/kWh = $40 e 6, the capex for batteries.
Battery Electric Compared to Diesel
At $20/kWh, over 25 year life, the design study electric ship saves $16 million in present dollars over diesel due to lower operating costs. Diesel opex is greater than excess electric ship capex. Breakeven battery cost is $56 million for 2,000,000 kWh, or $28/kWh.
Battery Life
At 40 trips per year, and with cycle life of 4,000 cycles, battery cycle life is 100 years. Battery calendar life can exceed 25 years. Diesel ship lifetime is 25 years. When higher battery and electric motor lifetimes are considered, electric ship cost advantages widen over diesel.
Conclusion
Calculations show a cross-Atlantic trip of 5,500 km from Rotterdam to New York requires 2 GWh of electricity at 17 knots, while average container speeds are 14 knots. The study example oversizes the battery requirement by 1.78 at the higher speed, allowing trip flexibility. In this scenario, modest near-future gravimetric energy density increases allow electric ship batteries to use less than 5% of cargo volume and weight. With passive cooling and battery safety, near-future SIB added battery volume and weight are under 5% of cargo for ships of 5,000 TEU or more, presenting an opportunity to use container ships as energy tankers.
Research shows diesel lifetime operating costs are high compared to capital costs. A diesel engine can cost $30 million, while annual operating costs can be about $10 million. High diesel operating costs tip the scales towards battery electric propulsion over a typical diesel ship lifetime. Diesel fuel costs exceed electricity costs by $1.5 million annually. Diesel annual maintenance costs can be $1 million, while electric maintenance costs are minimal. At $20/kWh, batteries can be lower cost than diesel ship propulsion for 5,000 km distances. BES versus diesel breakeven is at $28/kWh for 5,500 km range.
A recent study suggested that over 40% of global container ship volume could be electrified with batteries at $50/kWh. With lower costs and greater range, battery electric ships can do the majority of global container and bulk cargo ship volume. Interregional routes from Singapore to Shanghai, and from North Sea to Mediterranean, are likely first applications for 5,000 km electric ships. As demands for lower emission increase, diesel fuel costs and propulsion capex costs increase. Lower emission fossil fuels, scrubbers, hybrids, and synthetic fuel alternatives require additional costs, while renewables and battery costs fall. As battery costs fall, electrification presents a viable pathway to lower emissions. Since the time of this writing, VLSFO costs have soared, tipping the scales further toward electrification. Battery electric advantages go beyond cost toward security and reliability.
Update
At today’s VLSFO prices of about $750/mt, diesel fuel prices rise compared to the scenario $570/mt. Diesel fuel costs rise to $0.139/kWh. 2026 industrial electricity rates rise to $0.09/kWh, and after 96% efficiency is factored, $.0938/kWh. 40 trips/year x 2.0 e 6 kWh/trip x $ 0.139 – 0.094/kWh = $ 3.6 e 6/year electricity cost difference. Together with the $1 million maintenance difference, the total is $4.6 million annually. Over a 25-year lifetime at 4%, the present value is $53.5 million. The excess diesel cost is $40.5 million. Breakeven battery cost is $80.5 million for 2 million kWh, giving $40.25/kWh breakeven.
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