FeFe?CN?₆ And Ni₃S₂/MnO As Advanced Electrode Materials For Rechargeable Aqueous Batteries

Renewable energies,like solar and wind energy,have attracted much attention in the past decades,due to the great consumption and limited resources of conventional energies.In general,these renewable energies are converted to electric energy for practical applications.Thus,how to realize the high-efficient storage/release of electric energy is of importance.As one of most successful devices,lithium-ion batteries hold the advantages of high energy density,low self-discharging effect,and low weight.But they also have the drawbacks,such as flammable and expensive organic electrolytes,low diffusion coefficient of Li ions in organic electrolytes,and strict operation for fabrication.Rechargeable aqueous batteries?RABs?,another important type of batteries,would greatly mitigate these issues,because of aqueous electrolytes that could effectively lower the cost,increase ionic conductivity of salts,reduce the electrolyte flammability,and assemble easily in air as compared to organic electrolyte.These results make RABs quite promising in the future.However,these RABs face the challenges both from electrode materials and from electrolytes.Firstly,aqueous electrolytes only work within a narrow potential window?1.5-2 V?dependent on electrode over-potential and electrolyte salts.Secondly,electrode materials fitted within this potential window are quite limited.The ideal anode/cathode materials are supposed to make the best use of this potential window and achieve the specific capacity as high as possible.This work synthesized two electrode materials for RABs,PBA-structured FeFe?CN?₆ and Ni₃S₂/MnO,and evaluated their electrochemical performances.The main results about them are summarized as follows.1.FeFe?CN?₆ nanocubes were successfully synthesized by a modified co-precipitation method.Well-separated redox reactions,fair cycling stability and rate capability of FeFe?CN?₆ enabled it to be developed as a bipolar material in an aqueous sodium ion battery.The as-obtained full battery exhibited outstanding cycling stability and rate capability.It could deliver a capacity of 32.2 mAh g^-1 at 20 C(2 A g^-1),76%of the capacity at 2 C.After 200 cycles at 2 C,98%of the initial capacity was maintained for this battery,suggesting a good capacity retention.The high loading mass made the areal capacity to reach 0.143 mAh cm^-2 even after 200 cycles.2.Cauliflower-like precursor was grown on carbon papers by an electro-deposition process,and the Ni₃S₂/MnO composite was gained after annealing treatment.As a cathode material,the precursor showed undesirable performance between 0-0.6 V?vs.Hg/HgO?,because of its poor crystallinity.While Ni₃S₂/MnO composite,exhibited a specific capacity of 87.1 mAh g^-1 at 2 A g^-1 and an average discharge plateau at 0.43 V.After 450 cycles at 2 A g^-1,the capacity retention could be still kept at 97.5%,indicating the excellent stability.Compared to Ni₃S₂ alone,this composite was much better,confirming the synergistic effect of multi-components.