Chemists have developed a graphene-armoured anode designed to overcome sodium-ion batteries’ trade-off between charging speed and lifespan.
Interest in sodium-ion batteries has grown in recent years as researchers seek more sustainable alternatives to lithium-ion technology. Sodium is approximately 1000 times more abundant than lithium, potentially easing supply-chain constraints and reducing battery costs, although overall environmental impact depends on other components in the battery, supply chains and manufacturing. Sodium-ion batteries also offer several advantages, including high power output, rapid charging and reliable operation at low temperatures. However, sodium-ion batteries currently still exhibit lower power density and energy density than their lithium-ion counterparts.
Researchers in China have now addressed this trade-off by using ultrathin nanosheets of titanium dioxide wrapped in a graphene-based protective shell to create a battery anode. This offers a potential route to high-power sodium-ion batteries, with the key advance being not a new battery ingredient but a structural design that combines fast charging and long life under more demanding electrode conditions.
This architecture, says Wei Li at Fudan University, China, does several jobs at once. The nanosheets allow sodium ions to move in and out easily, helping the electrode charge and discharge quickly, while the graphene coating improves electrical conductivity and helps protect the anode’s structure. ‘Our design combines fast energy storage with long cycle life, even when considerably more active material is packed onto the electrode,’ he adds.
In tests, the electrode retained more than 90% of its capacity after 3000 cycles at a relatively high active-material loading. ‘Practical charging speed also depends on the cathode electrode and electrolyte,’ says Li. ‘Both must keep pace with our electrode and remain stable during repeated fast charging.’
The anode was made using established processing steps: forming the particles, coating them with carbon and heat-treating the material. ‘However, familiarity does not establish industrial scalability,’ says Li. ‘Maintaining the same thin sheets and uniform graphene wrapping across large batches remains unproven. We would need to demonstrate consistent quality, yield and performance using larger equipment, while assessing energy use and processing costs.’
Tengfei Song, a research fellow at the University of Birmingham, UK, who was not involved in the study, agrees. ‘This is a strong piece of fundamental research,’ he says. ‘The authors show that careful nanoscale and interfacial design can give a titanium dioxide anode unusually fast sodium-ion storage kinetics and very long cycle life, even at relatively high mass loading. However, I would see it mainly as a high-power materials concept rather than a commercially ready anode material.’
Although the material’s large surface area helps it store sodium quickly, it could make manufacturing more difficult and costly at scale, Song adds.
‘The main next step would be testing under more realistic full-cell conditions,’ says Song. This would mean testing the material in larger batteries, using practical amounts of active material and without the need for extra sodium to compensate for early losses. A test cell to emulate a normal battery environment would help establish whether the anode’s fast charging and long cycle life translate into useful energy storage in a practical battery, he concludes.
