Onboard energy storage systems’ energy density and safety would be improved by replacing Li-ion technology
New battery technologies can increase energy density and reduce risk compared with lithium (Li)-ion batteries. With growing demand for onboard energy storage on tugs, alternatives to Li-ion technology, which has fire risks both as an energy source and during transport, need to be found.
ABS principal engineer for corporate technology Mejdi Kammoun says different technologies could replace the liquid electrolyte used in Li-ion batteries, reducing risks to vessel safety. “Battery chemistry is evolving to reflect the emergence of new technologies, in the process addressing safety concerns and energy issues, providing dividends for maritime end users,” says Mr Kammoun.
Li-ion batteries use a liquid or gel electrolyte to deliver emissions-free energy at the point of use. They are ideal for fully electric propulsion, but vessels are limited by their distance from the charging station, which can be overcome by adding generators in hybrid propulsion.
New technologies including metal-air batteries (MABs), redox flow batteries, (RFBs), sodium metal chloride batteries (SMC) and solid-state batteries (SSBs) could offer increased energy density and reduced risk.
“These alternatives are in different stages of research, but they hold the potential for battery systems to become more practical and widespread in maritime applications in the future as the maritime industry further electrifies,” Mr Kammoun explains to Riviera Maritime Media.
SSBs are similar to Li-ion batteries but have solid electrolytes, which means they are smaller and lighter than liquid electrolytes, resulting in higher capacity or lower weight.
“Using a solid electrolyte also makes SSBs safer since solid electrolytes are not prone to thermal runaway like the flammable liquid electrolytes in Li-ion batteries,” says Mr Kammoun. SSBs are being tested with several different electrode and electrolyte materials, with lithium metal a popular anode due to its high energy density.
RFB operations are based on a chemical reduction and oxidation reaction between two liquid electrolytes in the battery cell. These electrolytes are stored in tanks and pumped into the cell as needed, reacting across an ion-selective membrane so the electrolytes are not mixed together.
“The electrolytes are redox pairs, able to reversibly react with each other to charge and discharge depending on the battery’s needs,” Mr Kammoun explains. ABS has recently issued a New Technology Qualification to the developer of a vanadium redox flow battery system, and plans to move into prototype testing later this year.
MABs have the same general structure as Li-ion batteries but use air as a cathode and have a metal anode, with zinc, aluminium and lithium among the leading metals researched currently. “Because the cathode uses oxygen in the air instead of a typical lithium oxide cathode, the theoretical specific energy is only limited by the capacity of the metal anode,” says Mr Kammoun. “This specific energy can be up to 10 times higher than that of a Li-ion battery depending on the MAB type.”
An SMC cell is a high-temperature secondary battery. Its cathode is based on metals, mainly nickel and common table salt, while the anode consists of molten sodium. “The anode and cathode are separated by a solid electrolyte made of a ceramic material that allows for fast transport of sodium ions at temperatures above 200°C,” says Mr Kammoun.
“There are no side reactions, and no gaseous elements are produced during the charge and discharge process, so the cell can be hermetically sealed without the need for any venting valve. The energy density of an SMC is comparable to that of a Li-ion battery.”
These new battery designs are currently undergoing fine-tuning at the prototype stage for various components such as battery cells, modules, packs and battery management systems before entering mass production. “We estimate that with the necessary testing, production and regulatory process, these new technologies could be widely available for marine applications by 2030,” forecasts Mr Kammoun.
New battery technologies may initially be more expensive than current Li-ion batteries due to the development of new materials and the need to scale up production. However, as the technology matures and production scales up, costs are expected to decrease.
Additionally, some new battery technologies such as sodium-metal, RFBs and MABs have the potential to significantly reduce production costs by using abundant material in their designs.
ABS recently agreed a sponsorship programme with Texas A&M Engineering Experiment Station to research topics including vessel electrification using battery technology to underscore and broaden its own research efforts.
“Together, these new technologies are a potential game changer in the application of batteries at sea,” says Mr Kammoun.
“By combining the advantages of a longer lifespan, greatly improved energy capacity and an improved safety profile, they have the potential to accelerate the energy transition in the maritime industry, supporting shipping’s global decarbonisation goals.”
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