Rising demand for electronic devices and electric vehicles has significantly increased reliance on secondary ion batteries. Although lithium-ion batteries have been popular for years, sodium-ion batteries (SIBs) are emerging as a promising alternative. However, SIBs face challenges in gaining broader acceptance due to slow ion kinetics that impact their performance. A recent development is a polymer-based binder called PMAI, which creates a functionalized solid electrolyte interphase. Research shows that when used as an anode binder, PMAI can significantly enhance the performance and cyclic stability of SIBs.
The global appetite for electronic devices and electric vehicles is expected to keep expanding, necessitating more powerful batteries that offer improved efficiency, performance, and safe storage. For over 30 years, lithium-ion batteries (LIBs) have dominated the secondary ion battery market. Yet, concerns over the declining availability of lithium due to unsustainable extraction practices, high costs, and uneven geographic distribution are pushing the search for alternatives.
This situation has prompted researchers and industry leaders to seek substitutes for LIBs. Sodium-ion batteries (SIBs) present an attractive option since sodium is plentiful, cost-efficient, and possesses a high electrochemical potential. Nevertheless, several challenges must be overcome before they can be commercially viable. One challenge is that sodium’s larger ionic radius compared to lithium leads to sluggish ion kinetics and stability issues in phase and interphase formations. Additionally, developing electrodes that are effective and compatible with both LIBs and SIBs is essential. Carbon-based materials, although promising for both types of batteries, also come with limitations.
To enhance the performance and stability of electrodes, Professor Noriyoshi Matsumi from the Japan Advanced Institute of Science and Technology (JAIST) and his doctoral student Amarshi Patra shifted their research focus to polymeric binders for SIB electrodes. Their recent study, published on September 12, 2024, in Advanced Energy Materials, introduced a new water-soluble poly(ionic liquid) binder called poly(oxycarbonylmethylene 1-allyl-3-methylimidazolium) (PMAI). Their findings revealed that PMAI as an anode binder exhibited remarkable electrochemical performance and cycle stability. “There’s a growing global demand for materials that facilitate fast charge-discharge rates and solve the slow ion diffusion issue in sodium-ion batteries. This polymer-based binder, with its dense ionic liquid functional groups, is key to developing high-performance electrode systems in SIBs,” said Prof. Matsumi.
To evaluate PMAI’s effectiveness, the researchers tested it as a binder for a graphite anode in LIBs and a hard carbon anode in SIBs. Their electrochemical assessments showed that the PMAI-based anode achieved impressive performance, recording high capacities—297 mAhg-1 at 1C for LIBs and 250 mAhg-1 at 60 mAg-1 for SIBs—along with excellent cycle stability, retaining 96% capacity after 200 cycles for SIBs and 80% after 750 cycles for LIBs.
Moreover, the experiments indicated improved ion diffusion coefficients, reduced resistance, and lower activation energy, which can be attributed to the densely polar ionic liquid groups and the development of a functionalized solid electrolyte interphase during binder reduction.
The enhancements in performance and stability from the full-cell tests using PMAI as the anode binder underscore the potential of this innovative material for secondary ion battery applications. “This type of material is well-suited for rapid charging energy storage systems in commercial settings, as it facilitates better sodium-ion diffusion. Our research will foster the development of advanced materials, laying the groundwork for new sodium-ion powered electronic devices and vehicles,” concluded Prof. Matsumi.
“This new poly(ionic liquid) represents a significant advancement. Poly(ionic liquids) have been extensively researched for various applications, including energy storage, biochemistry, sensing, and catalysis. Our densely ionic liquid functionalized polymer has the potential to be beneficial across these fields,” he added.
