Synthesis and characterization of lithium and sodium nickelates and cobaltates for application as cathode materials

Improving the electrochemical performance of cathode materials remains a pivotal challenge in the advancement of next-generation rechargeable energy storage systems. This study focuses on the synthesis and characterization of alkali transition metal oxide cathode materials: lithium cobaltate (LCO), sodium cobaltate (NCO), lithium nickelate (LNO) and sodium nickelate (NNO) by solid-state sintering method. Whereas the structural properties of these materials are reported extensively in the literature, the electrical conductivity data is lacking and is an essential requirement for fabricating rechargeable batteries and supercapacitors. It is found from X-ray diffraction studies that LNO samples contain mixed phases of Li 2 NiO 2.88 and Li 2 NiO 2 while Na 10 Co 4 O 9 and Na 5 CoO 4 exist in the NCO sample. The LCO and NNO samples contain single phases of LiCoO 2 and Na 5 NiO 4 respectively. The FTIR analysis reveals characteristic Ni-O and Co-O bond vibrations peaks. The FESEM studies show particles of size in the range of 0.2–0.6 µm, with strong agglomeration due to long duration thermal treatment at 600 o C for 24 h. The LNO, NNO and LCO samples are semiconducting and their electrical conductivity increases with increase in temperature, the conductivities of these samples are 1.24 × 10 2 mS‧cm −1 ,7.05 × 10 −3 mS‧cm −1 and 1.72 × 10 −3 mS‧cm −1 respectively at 313 K. The NCO sample is metallic; its conductivity decreases with increase in temperature, conductivity is 3.4 × 10 3 mS‧cm −1 at 313 K and 3.5 × 10 4 mS‧cm −1 at 3 K. At a low current density of 0.04 A g −1 , LNO sample exhibits a maximum specific capacitance of 1062 F kg −1 and a highest specific energy of 0.33 Wh Kg −1 at a specific power of 35 W Kg −1 . The cyclic voltammetry studies of all samples show that the specific capacitance of the samples decreases with increase in the scan rate, and their specific capacitance is in the range: 63–290 F kg −1 at a scan rate of 25 mV s −1 .