Rational design of FeF2-based cathode to realize high-performance potassium storage

Abstract

The poor electronic conductivity of conversion-type materials (CMs) and the dissolution/diffusion loss of transition metal (TM) ions in electrodes seriously hinder the practical applications of potassium ion batteries. Simply optimizing the electrode materials or designing the electrode components is no longer effective in improving the performance of CMs. Binders, as one of the electrode components, play a vital role in improving the electrochemical performance of batteries. Here we rationally designed FeF₂ electrodes for the first time by optimizing electrode materials with the introduction of carbon nanotubes (CNTs) and combined with a sodium alginate (SA) binder based on strong interactions. We show that the FeF₂@CNTs-SA cathode does not suffer from TM ion dissolution and delivers a high capacity of 184.7 mAh g⁻¹ at 10 mA g⁻¹. Moreover, the capacity of FeF₂@CNTs-SA is as high as 99.2 mAh g⁻¹ after 100 cycles at 100 mA g⁻¹, which is a twofold increase compared to FeF₂@CNTs-PVDF. After calculating the average capacity decay rate per cycle of them, we find that FeF₂@CNTs-SA is about one-third lower than FeF₂@CNTs-PVDF. Therefore, the SA binder can be broadly used for electrodes comprising several CMs, providing meaningful insights into mechanisms that lead to their improved electrochemical performances.