Limiting Factors in the Sodiation Kinetics of Sodium-Ion Battery Anodes

Sodium-ion battery (SIB) displays many of the properties similar to Li-ion battery such as operating principles and capacity, noticeably compressed the SIB cathode exploration period. Having said that, anode materials of Na-ion battery is still underperforming as the commercial graphite is inadequate in storing bulky Na ions. Alloying elements such as those used in Li-ion batteries can also be used for sodium-ion batteries. This alloying type of materials has the ability to absorb more charges and higher storage capacity.  It is essential to keep in mind that such materials exhibit huge volume expansion upon sodiation and hence, considerable mechanical stress upon cycling. In contrast to intercalating material, it is found that the SEI layer formed during the initial cycles undergo fracture and regeneration in further cycles causing a capacity to decay over time. The mechanism of charge storage (and removal) in the electrode essentially remains the same whether it is sodium or lithium. However, due to the fact that the sodium atom has a bigger radius and higher mass compared to the Li atom, the diffusion induced stress is much more prominent in this case. This may not only cause pulverization of electrode but can also result in loss of adherence of active material and the current collector. Thus, Sn has been selected as an exemplar system to study the properties of Na+ in a sodium-ion battery.

Ionic motions between electrode and electrolyte have a pivotal role in determining the battery response. Higher ion‐uptake capabilities of an electrode (alloy type) come with a price of large structural and morphological changes and a premature cell failure. The possibility of designing an electrode with essential properties requires a detailed analysis of the limiting factors related to the intercalation in an electrode and ionic transport through the electrode/electrolyte interface. In this study, we have focused on evaluating the effective kinetic and transport properties of an anode in the context of sodium-ion battery. Fick’s law based galvanostatic intermittent titration technique (GITT) analysis was conducted in the presence of different anionic group ( and ). Depending on cation-anion interaction energy, desolvation of different salts and the number of effective charge carriers will vary. Thus, we have compared the anionic effect on efficient transport of charge carriers in different electrolyte systems. Here we decided to wade through the fundamental properties like intercalation rate constant, exchange current density, and charge transfer resistance to have a better understanding with different levels of sodiation and de-sodiation. With a rich set of calculated parameters, this study will lay the foundation for the future development of the electrochemical model for a sodium ion system.