Effects Of Crystal Structures And Doping On The Performance Of Co-Based Selenide For Li/Na-Ion Batteries

More than ever before,the developments of rechargeable lithium ion/sodium ion battery?LIBs/NIBs?technology will continue unabated,driven by growing demand for portable consumer electronics,wearable and electronic devices,and large-scale energy storage.Negative electrode material is an important part of LIBs/NIBs,and the choice of its material type is very important to improve key battery parameters?energy density,cycle life,safety,etc.?.Co-based selenides of redox mechanism provide higher theoretical capacity based on multi-electron participation in chemical reactions,and become the most promising anode material for lithium/sodium ion batteries.However,the large volume change and voltage polarization during the charging and discharging process seriously hindered the application of Co-based selenides.Therefore,it is necessary to explore effective strategies to improve energy storage performance of Co-based selenides as anodes for LIBs/NIBs.The main results are as follows:?1?Hierarchically porous orthogonal CoSe₂?o-CoSe₂?and cubic CoSe₂?c-CoSe₂?spheres are prepared through a controllable selenization and subsequent annealing strategy.Both types of CoSe₂spheres exhibit superior electrochemical properties resulting from hierarchical architecture which can alleviate of the structural strain,the accelerate electron transmission and shorten the diffusion pathway of Na⁺.As anode materials for NIBs,the o-CoSe₂electrode delivers a higher rate capability of244 m Ah g^-1at 3000 m A g^-1and a better cyclability of 378 m Ah g^-1after 100 cycles at 1000 m A g^-1compared to the c-CoSe₂.From detailed microstructure characterization and kinetics behavior analysis,it is revealed that the o-CoSe₂spheres exhibits larger specific surface,more optimized porous nature,higher pseudocapacitive contribution,and more powerful Na⁺ions mobility.?2?A three-dimensional?3D?pomegranate-like porous bimetallic spheres?termed as NC@NCS?of nano-sized Ni Co₂Se₄particles as inner core and Ni Co₂Se₄layer/thin-walled N-doped carbon respectively as inner/outer shell is delicately synthesized by simple hydrothermal.Duing to the synergistic effects of intrinsic metallic characteristics,hierarchically porous structure,robust double shells,intimate nanosphere-N-doped carbon contact layer,NC@NCS show a capacity of 1401.6 m Ah g^-1after 500 cycles at a current rate of 0.5 A g^-1for LIBs and 433.9 m Ah g^-1after 1000cycles at 3A g^-1for NIBs.In the rate performance,the as-obtained NC@NCS exhibits excellent reversible rate capability with 513.3(at 11A g^-1)and 306.6 m Ah g^-1(at 20 A g^-1)for LIBs and NIBs,respectively.Kinetic analysis shows that the lithium/sodium storage in NC@NCS anode is mainly contributed by pseudocapacitance behavior,which is an important contribution to the charge transfer and stable long-term cycling.