On controlling the P2-O2 phase transition by optimal Ti-substitution on Ni- site in P2-type Na0.67Ni0.33Mn0.67O2 (NNMO) cathode for Na-ion batteries

Effect of Vanadium Substitution on the Ni-Site in P2-Type Na0.67Ni0.33Mn0.67O2 in Optimized Carbonate Ester Electrolytes as Cathode for Sodium-Ion Batteries

“…The Vsubstituted Na0.67Ni0.33-xVxMn0.67O2 electrodes show poor rate performances as compared to the pristine material. Similar behavior was observed when Ni-site was substituted by Ti 4+ -ions [20]. Ti-substituted Na0.67Ni0.33-xTixMn0.67O2 electrodes (x = 0.08 and 0.16) have displayed better C-rate performances only at capacity rates higher than 0.5C.…”

“…7a-c). P2-O2 structural transition is evident in P2-type Na0.67Ni0.33Mn0.67O2 electrodes in the form of a long voltage plateau at 4.2 V. The P2-O2 irreversible transitions that exist for the initial cycles significantly affect the capacity retention in these types of materials [20,43]. As seen from Fig.…”

“…Additional capacity due to Cu 2+ /Cu 4+ redox, improved capacity retention, and controlled phase changes enhance the electrochemical performance. A recent study on suppressing P2-O2 structural transition by optimum Ti-substitution reveals that the substituted electrodes can minimize the reversible capacity loss up to 12% during 50 chargedischarge cycles [20]. Aliovalently substituted cathodes have been studied at a full-cell level in order to realize practical applications.…”

Challenges of layer-structured cathodes for sodium-ion batteries

“…To suppress this phenomenon, doping some electrochemically active/ inactive elements (such as Mg, Zn, Al, Cu and Li) into Na x TMO 2 has been reported to be beneficial. 35,36,48,60,63,68,[72][73][74] 5.1.1 Cationic doping. Cationic doping is effective in inhibiting the irreversible phase transition, thus improving the electrochemical performance of layered oxides.…”

“…In general, the P2 and O3 phases undergo a series of phase transitions during the electrochemical cycle, involving different stacking sequences of the oxygen layer. 60 During the charging and discharging process, the P2 phase usually transits to the O2 phase due to the sliding of TMO 6 octahedral layers with the extraction of Na + . These problems result in a significant shrinkage of the crystal structure and a reduction in the distance between layers.…”