As rechargeable batteries, lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) have become indispensable products, but they come with drawbacks such as high cost, short lifespan, and unstable performance. To address these issues, scientists in Japan have developed a new type of polymer-based adhesive that can significantly improve battery performance.
Despite dominating the rechargeable battery market, the drawbacks of LIBs have led people to seek alternatives. Sodium-ion batteries have long been considered as a replacement for lithium-ion batteries due to the abundance and low cost of sodium in nature, as well as its higher electrochemical potential. However, SIBs also suffer from stability issues.
Currently, inexpensive carbon materials are used to make the anodes of lithium-ion and sodium-ion batteries. These anodes primarily rely on traditional non-ionic conductive adhesives such as polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR). However, these polymers cannot effectively transport lithium ions and sodium ions, greatly limiting the battery’s capacity ratio, charging speed, and cycle life.
Researchers at the Japan Advanced Institute of Science and Technology (JAIST) in the Hokuriku region have developed a new type of dense functionalized polymeric ionic liquid (DFPIL) adhesive. By combining the adhesive containing a large amount of water-soluble polymer PMAI (synthesized from multiple carbonyl methylene 1-vinyl-3-methylimidazolium) with the battery anode, they have found significant improvements in addressing the shortcomings when using PVDF.
In their experiments, researchers added the new PMAI material to the anode graphite of LIBs and the anode hard carbon adhesive of SIBs, and conducted electrochemical and cycle charge-discharge tests on these electrodes while also observing the internal changes using cross-sectional imaging.
The results showed that the LIBs based on PMAI in the anode exhibited a battery capacity of 297mAh/g at 1 Coulomb, while LIBs using traditional PVDF material only had a capacity of 228mAh/g. Furthermore, the capacity of the SIBs anode increased by nearly 30% when using PMAI compared to PVDF material.
Additionally, both LIBs and SIBs demonstrated excellent cycle stability. After 750 charge-discharge cycles, the LIBs using PMAI maintained a maximum capacity retention rate of approximately 80%, whereas those using PVDF had only 72%. Similarly, the SIBs maintained a capacity retention rate of 96% after 200 cycles with PMAI compared to 88% with PVDF material.
This indicates that both LIBs and SIBs exhibited superior electrochemical performance and higher capacity under the influence of PMAI material. The improvement in performance is related to the strong adhesion of PMAI on the active material and copper foil, providing stable electrochemical performance and alleviating the expansion of the graphite electrode after multiple charge-discharge cycles.
Furthermore, through instrumental analysis, researchers discovered that the structure inside the adhesive containing PMAI polymer was densely arranged, forming numerous channels conducive to the shuttle of sodium and lithium ions, allowing the ions to traverse through the carbon and graphite layers efficiently. This reduces resistance, enhances ion conductivity, and increases the battery’s capacity ratio.
These results are sufficient to demonstrate that LIBs and SIBs using PMAI polymer have good potential for practical applications and are expected to be applied to more rechargeable batteries in the future.
When asked what makes this new material stand out, Professor Noriyoshi Matsumi from the Japan Advanced Institute of Science and Technology explained to the school’s newsroom that the global demand for batteries with rapid charge-discharge capabilities has increased, thus requiring a solution to the slow sodium-ion diffusion in sodium-ion batteries. This polymer-based adhesive containing dense ionic liquid can effectively address the issues present in sodium-ion batteries.
He elaborated, “The new polymer (ionic liquid) is a new type of material that has been extensively researched for energy storage, biochemical applications, sensor applications, catalysis, and more. The new polymer we developed has potential applications in the various research areas mentioned above.”
The research findings were published on September 12th in “Advanced Energy Materials”.