Low cost & quasi solid state Na2Mn0.5Ni0.5Fe(CN)(6)//NaxFe2O3 hybrid Na-ion batteries for solar energy storage

Herein, we have explored low cost Prussian blue analogues (PBA), namely Na2MnFe(CN)(6) (Mn-PBA) and Na2Mn0.5Ni0.5Fe(CN)(6) (MnNi-PBA), as positive electrodes and iron oxides, namely Fe2O3 and Na-incorporated Fe2O3 (NaxFe2O3), as negative electrodes for quasi solid state Na-ion batteries. The detailed electrochemical characterization reveals the fact that MnNi-PBA shows superior positive electrode performances to Mn-PBA, while NaxFe2O3 depicts improved negative electrode performances with respect to Fe2O3. The comparative electrode performance data are corroborated by bond-valence energy landscape (BVEL) and density of states (DOS) calculations. Moreover, a 1.6 V full cell with MnNi-PBA positive and NaxFe2O3 negative electrodes is assembled in organic-inorganic hybrid hydrogel electrolyte, which demonstrates a specific capacity of 48 mA h g(-1) (@ 50 mA g(-1)), an energy density of 77 W h kg(-1) (@ 118 W kg(-1)), a power density of 803 W kg(-1) (@ 56 W h kg(-1)) and good cycle life (80% capacity retention after 250 cycles at 50 mA g(-1)) in the 0-1.6 V regime. Further, to validate the solar energy storage applications, a 3.2 V prototype device is fabricated by the series connection of two 1.6 V cells, which is capable to illuminate a 3 V/270 mW light-emitting diode (LED) setup, and successfully demonstrates a one week-long solar-charge/LED-discharge cycling module.