Researchers at Oxford University and Tokyo University of Science published separate studies on December 17 detailing advances in sodium-ion battery charging speeds and solid electrolytes that maintain conductivity.
Scientists at Tokyo University of Science showed that sodium-ion batteries using hard-carbon electrodes charge faster than conventional lithium-ion batteries. Professor Shinichi Komaba’s team applied a diluted electrode method, which involves mixing hard-carbon particles with electrochemically inactive aluminum oxide. This approach removes ion traffic jams that occur in dense composite electrodes during rapid charging.
The researchers conducted cyclic voltammetry and electrochemical analysis to evaluate ion movement. Their measurements indicated that sodium ions travel through hard carbon more quickly than lithium ions. The apparent diffusion coefficient, which quantifies ion mobility, proved higher for sodium than for lithium in general.
Komaba stated, “Our results quantitatively demonstrate that the charging speed of an SIB using an HC anode can attain faster rates than that of an LIB.” The study further revealed that sodium ions need less activation energy to create pseudo-metallic clusters inside hard-carbon nanopores. This property renders sodium insertion into the material less affected by temperature variations.
The Tokyo research appeared in the journal Chemical Science. These findings establish the intrinsic charging capabilities of hard-carbon anodes in sodium-ion batteries compared to lithium-ion counterparts.
At Oxford University, Paul McGonigal and PhD student Juliet Barclay developed cyclopropenium-based electrolytes. These organic materials retain ionic conductivity during the transition from liquid to solid states. This development counters the standard electrochemical observation that ion mobility drops sharply when liquids solidify.
The team synthesized disc-shaped molecules equipped with flexible side chains. Upon solidification, these molecules self-assemble into columnar structures. The design spreads positive charge evenly over a flat molecular core. This configuration avoids trapping negative ions and sustains a permeable setting that supports ion transport.
Barclay remarked, “We’ve demonstrated that it’s possible to engineer organic materials so that ion mobility does not freeze out when the material solidifies.” Tests in the study confirmed steady conductivity across liquid, liquid-crystal, and solid phases for different ion types.
Published in Science, the Oxford work highlights consistent performance in conductivity regardless of phase state. Manufacturers can heat these electrolytes to a liquid state during battery assembly. Cooling then produces stable solid forms that prevent leakage and reduce fire risks without compromising ion movement efficiency.
