No abstract

Hexagonal layered O3-NaNi 0.4 Mn 0.4 Co 0.2 O 2 is prepared by mixed hydroxide solid state reaction method at an optimum temperature of 800 °C. Rietveld refined PXRD pattern reveals single phase formation with space group R-3m. Galvanostatic electrochemical studies reveal reversible sodium de-insertion/insertion with concomitant structural phase transitions. In the voltage window of 2.2 -3.8 V, the first discharge capacities are 150 and 135 mAh g -1 at C/20 and C/6.5 current rates, respectively. The capacity retention is 80% after 33 discharge cycle at C/20 rate and 78% after 40 discharge cycle at C/6.5 rate. When the voltage window is increased to 1.6 -4.5 V, the initial discharge capacity is 173 mAh g -1 at C/10 rate and a capacity retention of 63% is observed after 10 discharge cycle. The O3 phase undergoes a series of structural transformations from O3, O'3, P3, P'3 and P3'' during charging and reverts to O3 phase upon deinsertion of Na during discharge. Structural stability is evident from ex-situ XRD studies even after 33 cycles, when cycled in the voltage window of 2.2 -3.8 V at C/20 rate.

Herein, we have explored performance of layered LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM111) cathode material for Li ion battery applications, prepared by different preparation strategies namely co-precipitated mixed hydroxide and solid state high temperature approach combined with high-temperature calcination. The effect of crystal structure and morphology of the obtained materials were characterized by means of X-ray diffraction and scanning electron microscopy. X-ray analysis reveals that the observed lattice parameter ratio c/a is greater than 4.89 for materials with different approaches, which indicates the formation of hexagonal layered α-NaFeO 2 structure. The electrochemical properties of the materials were thoroughly characterized by means of charge-discharge experiments and electrochemical impedance spectroscopy. The direct solid state synthesized NCM111 material exhibits a low retention and discharge capacity of 60 mAh g −1 at the end of 50 cycles with high irreversible capacity during cycling. The present studies have shown that the importance of material synthesis route and its sintering process, prepared at 900 °C for 8 h results low cation mixing between Li and metal ions layer in NCM111 lattice compared to other sintered samples, resulting in superior electrochemical performance. The reversible capacity of 175 mAh g −1 is noticed at C/10 rate within the voltage window of 2.5-4.4 V for 900 °C treated sample. Even at C/3 rate, a stable high reversible capacity of 145 mAh g −1 is obtained with high capacity retention of 95%. The Rietveld and EIS spectroscopic analysis conforms the existence stable layered structure and electrode, interface for NCM11 approached through co-precipitation.

No abstract