Preparation And Electrochemical Performance Of Anode Materials For Sodium/Potassium-ion Batteries

The uneven distribution and scarcity of lithium resources would hinder the further development of lithium-ion batteries?LIBs?.Sodium/potassium-ion batteries have been regarded as the most promising alternative,thanks to the high abundance,low cost and environmental benignity of sodium/potassium resources and also their similar working mechanism to LIBs.However,the radius of Na⁺/K⁺is larger than that of Li⁺,which makes that graphite as the anode of commercial LIBs,shows poor electrochemical performance using as the anode of sodium/potassium ion batteries.As a result,the discovery of suitable anode materials with high capacity,long cycle life and excellent high-rate property has become a major challenge for the development of the anode of sodium/potassium-ion batteries.Here,hollow Ni-NiO nanoparticles/porous carbon nanosheets?Ni-NiO/PCNs?as hybrid anode material in sodium-ion batteries?SIBs?with long cycle life were prepared using the template-removal method and the kirkendall effect;ultrasmall Fe₇Se₈nanoparticles/N-doped carbon nanofibers?Fe₇Se₈/N-CNFs?as hybrid anode material in SIBs with superior rate property were prepared by a facile electrospinning method;based on the above template-removal method and previous studies,ultra-high N-doped porous carbon nanosheet?N-PCNs?as carbon-based anode in potassium-ion batteries?PIBs?with excellent comprehensive electrochemical performances were prepared.The details are as follows:?1?As a candidate of the next-generation rechargeable batteries,SIBs have attracted great interest owing to the high abundance,low cost and environmental benignity of sodium resources.However,a shortage of appropriate anode materials with superior electrochemical performance has become the major bottleneck for their future development.Here,a unique hybrid material of hollow Ni-NiO nanoparticles embedded in PCNs was fabricated through a facile in situ synthesis strategy.As an anode in SIBs,the as-fabricated Ni-NiO/PCN electrode shows an ultra-long cycle life(a nearly unvarying capacity of 235.4mAh g^-1 at a current density of 1 A g^-1 even after 5000 cycles),which originates from the synergistic effect of high-content carbon,interconnected PCNs,metallic Ni phase,and hollow Ni-NiO nanoparticles.This work provides a promising strategy for rationally developing novel electrode materials for advanced energy storage devices.?2?On account of increasing demand for large-scale energy storage devices,SIBs have shown great potential to replace LIBs owing to the abundant reserve,low cost and environmental benignity of sodium resources.Here,we report a facile electrospinning method to fabricate a hybrid material of ultrasmall Fe₇Se₈ nanoparticles/N-CNFs.As an anode material in sodium-ion batteries,the Fe₇Se₈/N-CNF hybrid exhibits superior rate property with a specific capacity of 286.3 mAh g^-1 at a current density of 20 A g^-1,outperforming other metal selenides.Such an excellent performance originates from the synergistic effects of ultrasmall Fe₇Se₈ nanoparticles as well as the unique and interconnected network of N-rich CNFs,which offer short Na⁺diffusion distance,provide efficient electrolyte diffusion paths,supply numerous defects and active sites for Na⁺adsorption,enhance surface pseudocapacitive behavior,improve the electronic conductivity,and thus facilitate the electron/ion transport and electrochemical reaction kinetics.?3?PIBs are a promising alternative to LIBs owing to their low-cost,high safety,and low redox potential of K/K⁺.However,it is still a challenge to achieve fast charging/discharging and long cycle life with the current electrode materials because of the intrinsic large ionic radius and heavy molar mass of K⁺.Here,we report a template-removal method to fabricate a 3D interconnected N-PCNs,which exhibits superior electrochemical properties as an anode material in PIBs,high rate property of127.5 mAh g^-1 at a current density of 5 A g^-1 and cycling stability of 151.2 mAh g^-1 after10000 cycles at 1 A g^-1.These remarkable performances are attributed to ultra-high N doping and a high specific surface area with abundant hierarchical pores,which provides a large amount of active sites for K⁺insertion/extraction,enhances the electronic conductivity,and offers efficient electrolyte diffusion paths.Density functional theory?DFT?calculations demonstrate that pyrrolic and pyridinic-N doping can promote the adsorption of K⁺on the N-PCN electrode,which promotes K⁺storage.