Effects of multi-element composition regulation on the structure and electrochemistry of P2-type layered cathode materials.

P2-type Mn-based oxides are promising cathode materials for sodium-ion batteries due to their low cost and high capacity virtue. However, the irreversible phase transition and unstable anion redox at high operating voltages (∼4.2 V) will cause structural distortions, leading to slow sodium-ion diffusion kinetics and severe capacity degradation. Herein, a multi-elemental composition regulation strategy is proposed to enhance the structural stability of P2-type cathode by optimizing the structure and modulating the irreversible oxygen redox during high-voltage cycling. A series of multi-element cathodes Na 0.67 (Fe 1/4 Co 1/4 Ni 1/4 Ti 1/4) 1-x Mn x O 2 (x = 0.4,0.5,0.6,0.7,0.8,0.9) are designed and the effects of component modulation on their structure and electrochemical behavior are systematically investigated. Especially, the optimized Na 0.67 Fe 0.05 Co 0.05 Ni 0.05 Ti 0.05 Mn 0.8 O 2 cathode maintains P2 phase during the initial charging/discharging between 1.5 V and 4.5 V, inhibits irreversible oxygen redox, and exhibits small lattice expansion. Impressively, the above optimized cathode exhibits superior cycling stability with capacity retention of nearly 90 % and reversible capacity of 130.1 mAhg−1 after 100 cycles at 1C rate. Furthermore, the optimized cathode also displays an excellent rate capability (capacity of 108.2 mAh g−1 at 5 C rate) due to the enhanced Na+ diffusion kinetics. This work provides new insight into developing high-stable Mn-based oxide cathodes operating at high voltage for sodium-ion batteries. [Display omitted] • The effects of multi-element component modulation are investigated. • The Mn-rich multi-element samples maintain excellent structural stability. • The Mn-rich multi-element samples suppressed the irreversible oxygen redox. [ABSTRACT FROM AUTHOR]