An article written by Engelbert Hopf and Ralf Higgelke for Markt&Technik, with the collaboration of Shalu Argawal, PhD, Technology & Market Analyst, Power Electronics & Materials from Yole Développement (Yole).
Up until now, lithium-ion batteries have been inextricably linked to electromobility. This could now change, as CATL has unveiled a marketable sodium-ion battery. Markt&Technik asked experts from science and industry for their assessment.
Post-lithium batteries, which are an alternative to lithium-ion systems, have so far only been a promise from the research labs. A few weeks ago things changed. Dr Robin Zeng, Chairman of China’s largest battery producer, Contemporary Amperex Technology, unveiled the first generation of marketable sodium-ion batteries at a technology conference hosted by his company. They offer an energy density of 160 Wh/kg; they have already started to be rolled out to industry.
Sodium-ion batteries operate on a similar principle to lithium-ion batteries. In the rocking chair principle, sodium ions move back and forth between the anode and cathode of the cell. Since sodium ions are larger than lithium ions, the requirements placed on the structural stability and kinetic properties of the materials are higher. This previously hindered the industrialisation of sodium-ion batteries. CATL now uses Prussian white with a high specific capacity as cathodes and has additionally reshaped the structure of the material by rearranging the electrons. In this way, the rapid capacity fade during cyclic charging and discharging can be overcome.
For the anode, the company has developed a hard carbon material that is characterised by a special porous structure. This allows sodium ions to be stored on a large scale and transported quickly; cycle stability is also improved in this way. Currently, the energy density of the cells is 160 Wh/kg. At room temperature, the cells can be charged to 80 per cent in 15 minutes. In addition, the cells can retain more than 90 per cent of their capacity at an ambient temperature of -20 °C. Dr Zeng announced that CATL’s next step would be to increase the energy density of the cells to 200 Wh/kg. This would then correspond to the current energy density of lithium-ion cells.
‘CATL’s advance could be the breakthrough for sodium-ion battery technology,’ assesses Professor Andreas Jossen, holder of the Chair of Electrical Energy Storage Technology at the Technical University of Munich. ‘In the past, however, only energy densities of around 100 Wh/kg were achieved, so the technology was not considered for electric vehicles.’
In addition to the fact that existing production lines for lithium-ion cells can be converted to sodium-ion cells, as CATL indicates, Professor Jossen believes that the main arguments in favour of sodium-ion technology as a cheaper alternative to lithium-ion systems are the use of inexpensive materials – copper, cobalt, nickel and lithium can be dispensed with – and less energy-intensive manufacturing processes (graphite). The only drawback so far: about 30 per cent more installation space would be required for the battery.
In Germany and Europe, however, says Professor Jossen, ‘sodium-ion technology has to date been neglected somewhat, so there is not so much research activity on it.’ An assessment shared by Dr Ulrike Wunderwald, head of the battery materials working group at Fraunhofer IISB in Freiberg: ‘We have not yet examined sodium-ion technology in detail.’
Freiberg is currently working on aluminium-ion batteries as a potential successor to lithium technology. In laboratory systems, an energy density of 135 Wh/kg in relation to the active mass has already been achieved with graphite powder as the cathode. In her view, the following applies to both sodium and aluminium systems: ‘Due to the predicted enormous demand for electrical storage, alternative battery technologies based on readily available and low-cost materials will be in demand.’ She is also convinced ‘that a lower-cost technology with the same or only slightly smaller performance always has the chance to capture market share from other technologies.’
Professor Stefano Passerini, coordinator of the EERA Joint Programme on Energy Storage and director of the Helmholtz Institute Ulm, calls the CATL initiative ‘a significant initiative’ and sees ‘Europe once again forced into the role of latecomer.’ Even though, at 160 Wh/kg, the first generation of sodium-ion cells are still well below the 200 Wh/kg of lithium-ion batteries, ‘in extreme cases they can replace them in all those applications that do not require high energy, such as stationary applications, light commercial vehicles, urban transport, delivery services, refuse collection or city cars and scooters.’
‘Their biggest advantage over lithium-ion batteries lies in the abundant and inexpensive raw materials,’ Dr Shalu Argawal also confirms. The analyst at Yole Développement continues: ‘Almost all the lithium in the world comes from four countries: Australia, Chile, China and Argentina. Moreover, the extraction of lithium is not environmentally friendly, while sodium is over a thousand times more abundant than lithium in the earth’s crust.’ This makes both sodium and corresponding batteries much cheaper than their lithium counterparts. ‘In addition, the cathodes of lithium-ion batteries typically use cobalt, a metal of limited availability that is associated with significant environmental and humanitarian problems. Sodium metal oxide is usually used for the cathodes of sodium-ion batteries,’ says the analyst.
A recent survey by Markt&Technik among leading battery manufacturers shows that they do not seem to have opted for sodium-ion batteries so far. For example, Oliver Sonnemann, Department Head Battery Sales at Panasonic Industry Europe, states that ‘we do not see sodium-ion batteries as the technology of the future and are instead moving in other directions.’ GS Yuasa would not give an assessment of the potential of sodium-ion systems.
Holger Gritzka, CEO of battery start-up Blackstone Technology, gives sodium-ion batteries a chance ‘if we succeed in compensating for the chemical-physical disadvantages of sodium compared with lithium in the cell design.’ Sodium-ion systems will not be a replacement for lithium-ion systems in the foreseeable future, ‘but they could be a useful addition for certain applications over a long period of time.’ Ultimately, however, he too sees only sodium-ion and lithium solid-state batteries as a long-term, marketable alternative to conventional lithium-ion systems.
And how do potential users such as battery assemblers assess the market opportunities for sodium-ion systems? ‘I don’t think they are suitable for the consumer market,’ says Werner Suter, Managing Director of Tefag Elektronik; ‘the energy density is still too low for that.’ However, he sees possibilities for stationary and automotive applications, ‘but that will take time.’ An assessment that is also shared by the ZVEI. There, it is currently expected that further cell technologies will be ready for the market in about the second half of this decade, which could compete with the established lithium-ion systems: ‘These could include sodium-ion batteries and also solid-state batteries.’
Dr Martin Busche, Director of Engineering at Akasol in Darmstadt, currently sees sodium-ion batteries as a complement: ‘CATL opted for the better fast-charging capability and the better low-temperature performance when they were unveiled. The low energy density should be offset by the combination with high-energy LIBs.’ Akasol sees market opportunities for sodium-ion batteries, as Na- and Li-ion batteries are similar in terms of production processes ‘and so you can use LIB equipment for NIB batteries as well, and thus take advantage of the cost benefits from the ever-improving production lines.’
For Dr Tim-Patrick Fellinger, battery researcher at the Federal Institute for Materials Research and Testing (BAM), the market opportunities for sodium-ion batteries also appear realistic, as the increasing demand for lithium-ion batteries can hardly be met by production in the short term. ‘Since the production capacity for sodium-ion cells could be ramped up quickly, these can offer an alternative. In addition, sodium-ion cells can be produced in a more environmentally friendly way and at a lower price,’ Fellinger sums up.
Read the original German article on Markt&Technik…
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