The standard lithium-ion battery (LIB) using graphite electrodes has become exceedingly important in today’s world. Everything from electric cars to solar energy storage systems need these batteries, and the capabilities and progress of these devices rely on the steady advancement of battery technology. However, lithium is a scarce resource and is projected to run out with the ever-increasing demand we are placing on it. For this reason, we are investigating sodium ion batteries (SIB) as an alternative to LIB.

While many methods have been studied to improve SIB capacities and lifespans, our method stands out by using antimony nanobelts incorporated into an asymmetric membrane structure as a high performance anode material for SIB due to its theoretical capacity of 660 mAh g^-1 compared to hard carbon-based SIB (300 mAh g^-1)^. In addition to the asymmetric membrane structure, we use a carbon coating around the membrane which can further improve performance and stability. Embedding these group V nanomaterials within an asymmetric membrane structure coated in carbon will accommodate the large volume expansion of Sb-based SIB anode, enhance mechanical strength, and prevent rapid capacity loss due to leaching of cracked materials.

Herein, we demonstrate that the capacity and the cycling performance of SIB can be significantly improved over not only current SIB but also LIB. Preliminary results indicate that Sb nanobelts incorporated into an asymmetric membrane exhibit increased performance as a sodium-ion battery anode compared to Sb nanoparticle membranes, furthermore, dip coating the asymmetric membranes with a carbon based solution increases both capacity and cycling performance compared to membranes with no extra carbon coating. The batteries made using the dip coated Sb nanobelt asymmetric membranes show a specific capacity between 630 and 650 mAh g^-1 with a capacity retention of 99.4 percent over 45 cycles and an initial capacity loss of only 14 percent. In addition to electrochemical tests, we have also characterized the samples using scanning electron microscopy, energy dispersive x-ray spectroscopy, thermal gravimetric analysis, powder x-ray diffraction spectroscopy, and RAMAN spectroscopy to identify and quantify the materials in the membranes and starting materials. Using these characterizations, we were able to confirm the chemical composition and morphology of the Sb and C in our membranes. Thereby a scalable and cost-effective method of increasing capacity of NIB, while maintaining relatively good life cycle longevity has been developed by our research laboratory.