RESUMO
Due to high volumetric energy density, the major market share of cathode materials for lithium-ion batteries is still dominated by LiCoO2 (LCO) at a 3C field. However, a number of challenges will be triggered if the charge voltage is increased from 4.2/4.3 to 4.6 V to further increase energy density, such as a violent interface reaction, Co dissolution, and release of lattice oxygen. Here, LCO is coated with the fast ionic conductor Li1.8Sc0.8Ti1.2(PO4)3 (LSTP) to form LCO@LSTP, while a stable interface of LCO is in situ constructed by the decomposition of LSTP at the LSTP/LCO interface. As decomposition products of LSTP, Ti and Sc elements can be doped into LCO and thus reconstruct the interface from a layered structure to a spinel structure, which improves the stability of the interface. Moreover, Li3PO4 from the decomposition of LSTP and remaining LSTP coating as a fast ionic conductor can improve Li+ transport when compared with bare LCO, and thus boost the specific capacity to 185.3 mAh g-1 at 1C. Benefited from the stable interface and fast ion conducting coating, the LCO@LSTP (1 wt %) cathode delivers a high capacity of 202.3 mAh g-1 at the first cycle (0.5C, 3.0-4.6 V), and shows a higher capacity retention of 89.0% than LCO (50.9%) after 100 cycles. Furthermore, the change of the Fermi level obtained by using a kelvin probe force microscope (KPFM) and the oxygen band structure calculated by using density functional theory further illustrate that LSTP supports the performance of LCO. We anticipate that this study can improve the conversion efficiency of energy-storage devices.
RESUMO
Sodium-ion batteries (SIBs) have inspired the potential for widespread use in energy storage owing to the advantages of abundant resources and low cost. Benefiting from the layered structure, 2D-layered materials enable fast interlayer transport of sodium ions and thus are considered promising candidates as anodes for SIBs. Herein, a strategy of adjusting crystal orientation is proposed via a solvothermal method to improve sodium-ion transport at the edge of the interlayers in 2D-layered materials. By introducing surfactants and templates, the 2D-layered V5 S8 nanosheets are controlled to align the interlayer diffusion channels vertically to the surface, which promotes the fast transport of Na+ at the edge of the interlayers as revealed by experimental methods and ab initio calculations. Benefiting from the aligned crystal orientation and rGO coating, the vertical-V5 S8 @rGO hybrid delivers a high initial discharge capacity of 350.6 mAh g-1 at a high current density of 15 A g-1 . This work provides a strategy for the structural design of 2D-layered anode materials by adjusting crystal orientation, which demonstrates the promise for applications in fast-charging alkaline-ion batteries.
