Synthesis And Performance Of Pristine And Copper Doped Prussian Blue Analog For Sodium Ion Batteries

Pristine Prussian Blue?PB?and Prussian Blue Analogs?PBA?of high capacity and high cycle stability are fundamentally and technologically important for sodium ion batteries?SIB?.Currently pristine and doped PBAs are becoming a hot research area these material are cheap,enviromentally friendly,easy to synthesise and have good theoretical capacity.The focus of this work was on synthesis and electrochemical performance evaluation of pristine asnd copper doped PBA.Pristine Prussian Blue?PB?and copper doped Prussian Blue Analog?PBA?materials were synthesized by harnessing combined advantageous effects of sodium citrate,PVP and low temperature.When synthesizing PB and PBA materials,the main precursors that were reacted are sodium hexacyanoferrate Na₄Fe?CN?₆,iron?II?chloride tetra hydrate?FeCl₂.4H₂O?and copper?II?chloride dihydrate?CuCl₂.2H₂O?while PolyVinylPyrrollidone?PVP?,sodium citrate?Na₃C₆H₅O₇.2H₂O?and sodium chloride?NaCl?were used as additives.Throughout the experiments,all precursors and other additives were kept constant while temperature,amount of sodium citrate and the ratio of iron to copper were being optimized/changedThe PB sample synthesized using less sodium citrate at 25^oC?NPB-1?delivered reversible specific capacity of 132 mAh/g at 1C with 40%capacity retention after 150cycles.Increasing amount of sodium citrate during synthesis to at25^oC?NPB-2?led to a reversible specific capacity of 97 mAh/g at 1C with capacity retention of 70%after 150cycles.Conducting the experiment at 0^oC led helped to slow down nucleation and crystal growth there by reducing the number vacancies,increasing the sodium content and improving crystallinity.This helped to obtain a capacity retention of over 78.4%after 150th cycle at 1C.The amount of sodium citrate,the ratio of Fe:Cu and temperature,all had direct effect of the electrochemical performance of copper doped PBA.The copper doped PBA sample synthesized using Fe:Cu=3:2 at 25^oC?NPBC-1?has initial discharge specific capacity of 64 mAh/g and a capacity retention of 59%after 300 cycles.However when the same ammount of sodium citrate was used,changing the ratio Fe:Cu=3:1 at 25^oC?NPBC-4?,the initial discharge specific capacity increased 110mAh/g and a capacity retention of 56%after 300 cycles.From a wide range of the results,it is observed that initial specific discharge capacity increases as the ratio of Fe:Cu decreases?amount of copper decreases?.This shows that copper does not really contribute to the specific discharge capacity but helps to improve the capacity retention because it improving the rigidity of the PBA crystals so that it does not easily collapse during cycling.The effects of temperature on copper doped PBA were similar to what was observed in pristine PB.In a nut shell,it was found that,while optimizing temperature and amount of sodium citrate helps improve both capacity and capacity retention of PB and PBA samples,optimization on coper doping only helps improve capacity retention.