Suppressing oxygen redox in layered oxide cathode of sodium-ion batteries with ribbon superstructure and solid-solution behavior

Sodium-ion batteries(SIBs)are proved as one of the most acceptable candidates for replacing lithium-ion batteries in some fields by virtue of a similar“rocking chair”mechanism and the abundance of sodium.The voltage,rate performance,and energy density of these batteries are mainly determined by the cath-odes.Hence,a Li-Ni-Co co-substituted P2-Na_(0.67)[Li_(0.1)(Mn_(0.7)Ni_(0.2)Co_(0.1))_(0.9)]O_(2)(NLMNC)with ribbon super-structure is prepared with the aim of multi-ion synergistic modification.Owing to the addition of Ni and Co,the Jahn-Teller distortion of Mn can be suppressed corresponding with the improved structural stability,and a little bit of oxygen redox activities is triggered.When with the substitution of 10%Li,the X-ray diffraction(XRD)peaks of NLMNC show the ribbon superstructure at about 21°and 22°.The smooth charge/discharge profiles of the NLMNC cathode exhibit the solid-solution reaction.In addition,the platform at high voltage disappears corresponding with the existing oxygen redox activities being suppressed which may be related to the ribbon superstructure and the promotion of the Ni redox.Such NLMNC cathode can deliver a reversible discharge capacity of 123.5 mA h g^(-1)at 10 mA g^(-1).Even if the current density increases to 500 mA g^(-1),a reversible discharge capacity of 112.8 mA h g^(-1)still can be ob-tained.The distinguished cycling stability is related to the reversible migration of Li+between the metal oxide layer and the interlayer and low volume change during cycling.It is also needing to be mentioned that the capacity retention of NLMNC cathode is about 94.4%(based on the highest discharge capacity)after 100 cycles.This work presents an effective route to develop high-performance cathodes for SIBs.

In situ constructing(MnS/Mn_(2)SnS_4)@N,S-ACTs heterostructure with superior Na/Li-storage capabilities in half-cells and pouch full-cells

Effective design of nanoheterostructure anode with high ion/electron migration kinetics can give electrode with superior electrochemical performance.However,the design and preparation of nanoheterostructure composites with high-capacity and long cycling life in half and pouch full cells remain a big challenge.Here,a novel micro-pore MnS/Mn_(2)SnS_(4)heterostructure nanowire were in situ encapsulated into the N and S elements co-doped amorphous carbon tubes(abbreviated as(MnS/Mn_(2)SnS_(4))@N,S-ACTs)and showed superior energy storage properties in Na-/Li-ion half cells and pouch full cells.The Na-/Li-storage capabilities improvement are attribute to the strong synergistic effect between MnS/Mn_(2)SnS_(4)heterostructure and N,S-ACTs protective layer,the former induces an local built-in electric field between Mn_(2)Sn S_(4)and MnS during charging/discharging,accelerating interfacial ion/electron diffusion dynamics,the latter effective maintains the morphology and volume evolution during Na~+/Li~+charging/discharging,achieving a long-term cycling stability(e.g.,high discharge capacity of 79.2 mAh/g with the capacity retention of 79.3%can be gained after 2200 cycles at 3 C in(Mn S/Mn_(2)Sn S_(4))@N,S-ACTs//LiFePO_(4)pouch full cells;a high capacity of~34 mAh/g at 10 C can be got with a Coulombic efficiency of 100%after 1000 cycles in pouch(Mn S/Mn_(2)Sn S_(4))@N,S-ACTs//Na_(3)V_(2)(PO_(4))_(2)O_(2)F full cells.