New age electrode with densely functionalized polymeric binder for high-performance lithium and sodium-ion batteries

This has led researchers and the industry to find an alternative to LIBs. A promising contender is sodium-ion batteries (SIBs) because sodium is abundant in nature, is cost-effective, and has high electrochemical potential. However, certain issues need to be addressed before implementing them for commercial applications. First, the ionic radius of sodium is larger than lithium which gives rise to slow ion kinetics and complications in phase stability, and interphase formation. Second, there is a need to develop electrodes that are compatible and ensure high performance with not only LIBs but also SIBs. Moreover, carbon-based materials make promising electrodes for LIBs and SIBs, but they are not without their own set of flaws.

To help improve the performance and stability of electrodes, Professor Noriyoshi Matsumi from Japan Advanced Institute of Science and Technology (JAIST), Japan with his doctoral course student Amarshi Patra at JAIST, shifted their focus towards polymeric binders for manufacturing electrodes in SIBs. In their recent study published in Advanced Energy Materials on 12 September 2024, they developed a new densely functionalized and water-soluble poly(ionic liquid), poly(oxycarbonylmethylene 1-allyl-3-methyimidazolium) (PMAI) and tested its binding ability for LIB and SIB. The PMAI-based anodic-half cell showed excellent electrochemical performance and cyclic stability. "There has been a worldwide increase in demand for materials enabling fast charge-discharge and resolving the slow kinetics issue of sodium-ion diffusion. This polymer-based binder with dense ionic liquid functional groups acts as a component of high-performing electrode systems in SIBs," explained Prof. Matsumi when asked what sets this new material apart.

To test the effectiveness of the new PMAI material, the researchers used it as a graphite anode binder and hard carbon anode binder in LIB and SIB, respectively. The results from electrochemical evaluation revealed that PMAI-based anodic-half cell showed exceptional electrochemical performance, high capacities (297 mAhg^-1 at 1C for LIBs and 250 mAhg^-1 at 60 mAg^-1 for SIBs) and great cycle stability with 96% capacity retention after 200 cycles for SIBs and 80% capacity retention after 750 cycles in LIBs.

Furthermore, the experimental results showed improved ion diffusion coefficient, lower resistance and activation energy, attributed to the densely polar ionic liquid groups and the formation of a functionalized solid electrolyte interphase via binder reduction.

The improvement in performance and stability, as evident from the full-cell examination with PMAI as the anode binder is a testament to the novel material's potential as a binder for secondary ion battery applications. "This class of materials will be adopted in fast-charging energy storage systems for commercial applications, as this binder promotes improved sodium-ion diffusion. This study will encourage the development of more advanced materials, paving the way for new sodium-ion powered electronic devices and electric vehicles," concludes Prof. Matsumi.

"The developed novel poly(ionic liquid) is a novel class of material. Poly(ionic liquid)s have been intensely studied for a variety of applications such as energy storage devices, biochemical applications, sensing applications, catalytic applications etc. Our novel densely ionic liquid functionalized polymer has potential utility for above-mentioned various research field."