High crystallinity, preferred orientation and superior reversible capacity P2–Na0.67Ni0.25Mn0.75O2 thin film as cathode material for wide voltage sodium-ion battery

As a desirable cathode material for microelectronic energy storage devices, high performance P2–Na0.67Ni0.25Mn0.75O2 thin films were prepared on stainless substrates using pulse laser deposition. To unlock their cyclability and rate capability, the substrate temperature as well as post deposition annealing was varied from 350 to 750 °C. The crystal structure and surface morphology were measured as functions of temperature, showing an enhancement in crystallization and a formation of textured grains with the c-axis. The charge/discharge tests demonstrate that the thin-film deposited at 550 °C owns the highest reversible capacity of 166.3 mAh g−1 after 130 cycles at 13 mA g−1, corresponding to the initial value of 90.6%. As compared with the datum reported before, the as-deposited film-type P2–Na0.67Ni0.25Mn0.75O2 cathode material exhibits superior cycling performance and high reversible capacity in the wide operating range from 1.5 to 4.3 V, which should be due to the enhancement of a stable P2–O2 phase transition platform at around 4.2/4.1 V. These outstanding results would endow P2–Na0.67Ni0.25Mn0.75O2 thin film cathode material with great potential for application in high power and energy density sodium-ion batteries.