Na0.67Mn0.33Ni0.33Co0.33O2: Effect of synthesis technique on competing P3 and P2 phases

Abstract

In layered NaxTMO2 (TM = transition metal) common understanding attributes the emergence of P2 and P3 phases to the synthesis temperature. In this work, we show that the synthesis technique is the main responsible for these phases. We synthesize Na0.67Mn0.33Ni0.33Co0.33O2 with two techniques, solid-state and electrospinning, using two temperatures, 700 °C and 900 °C. Both electrospun samples sintered at 900 °C and 700 °C show single phase P2 and P3, respectively. Both solid-state synthesized samples at 900 °C and 700 °C show mixture of P2/P3. Electrochemical properties of the sample with only P3 phase has the highest initial capacity of 130 mAhg−1 at C/3 rate. The sample with only P2 phase has very stable cycle performance with 87 % capacity retention over 100 cycles consistent with its large interlayer separation. Our results show that the synthesis technique plays a crucial role in the crystal structure and the electrochemical performance of the layered cathode materials for Na-ion batteries.