Depending on the stoichiometry, sodium manganese oxides mainly have two kinds of structures: (i) layered structure (e.g. Na0.7MnO2.05) or (ii) tunnel structure (e.g. Na0.44MnO2), both having large number of vacancies accommodating constituent Na-ions. Na0.44MnO2 is particularly attractive as cathode in NIB because of its unique 3D crystal structure, which greatly facilitates Na+ mobility whereas Na0.7MnO2.05 is good candidate for cathode in NICs owing to its sloppy discharge profile. Here, ultrasonic sonochemical synthesis has been employed to obtain the target compounds, which restricts the final high-temperature annealing duration within 1-2 h. Herein, we will present (i) single crystalline Na0.7MnO2.05 nanoplates with preferential growth in (100) direction facilitating efficient Na+ (de)insertion leading to capacity over 140 mAh/g (average voltage = 2.4 V) and (ii) orthorhombic Na0.44MnO2 having a reversible capacity of 110 mAh/g (average voltage = 2.3 V). The salient features of sonochemical synthesis, structure, morphology and final electrochemical performance of NaxMnO2 oxides (both as NIB and NIC) will be presented combining experimental work as well as first-principle calculations.