Potency of Potassium Doping on Na-Ion Sites to Avert Phase Transition in P2 Type Sodium-Ion Battery

Sodium-ion battery (SIB) is acquiring considerable attention as a viable replacement to lithium-ion battery (LIB) technology in the ever-expanding energy storage market due to its attractive combination of homogeneous profusion in the earth and identical intercalation chemistry to LIB. However, SIB is still a laboratory child as SIBs exhibit slightly lower energy density as compared to those of LIBs. Hence, it is critical to determine a suitable cathode to facilitate facile Na-ion transport as cathode is the key factor affecting cycle life, energy density as well as safety. In case of SIBs, layered transition metal oxides are widely preferred as cathode material due to their excellent high specific capacity as well as their simple synthesis process. In this research, Manganese enriched P2 type quaternary Na 0.6 Fe 0.48 Mn 0.5 Ti 0.01 V 0.01 O 2 (NFMTV) cathode material is studied which shows high capacity and high voltage (4.2V) along with reducing Jahn-Teller (JT) Effect. However, inferior reversibility and capacity fading have still been a challenge, particularly for higher voltage window as lower Na content during discharge process initiates the unavoidable phase transition. To preserve the lattice orientation, a feasible approach is demonstrated in this research by introducing potassium (K) ion into Na ion sites between transition metal oxide (TMO 2 ) layers. This work explains that the K + into Na + ion layers serve as the supporting pillar to hold the stacking pattern intact even for very low Na content at higher voltage. As seen from the SEM and EDS analysis, no apparent alternation happened in surface morphology and crystal structure for a small amount of K doping. Furthermore, the XRD and Rietveld refinement results validate that emplacement of K + ions in the Na sites in the NFMTV crystal structure. It also expands the Na + ion diffusion path and substantially boosts the rate performance and reversibility. Besides, K + ion doping halts the gliding phenomenon and hence, phase transition is impeded which is observed from the improved cyclability and capacity retention.