Quench-Induced Surface Activated Layer Of Nanosphere Fe₂O₃,Ag/Fe₂O₃ For Lithium-Ion Battery Anode Materials

Improving the electrochemical performance of nanomaterials when used in the anode of lithium-ion batteries has been an important research direction in the field of lithium-ion batteries.Among the numerous methods of modification of nanomaterials,it has been verified that the surface chemistry of solid electrode materials plays a crucial role in the repeated charging and discharging process of batteries.Based on this research trend,this study examines nanomaterial surface modification techniques in detail and selects Fe2O3 material as the object of study.Using high temperature calcination and subsequent quenching operations,the surface chemistry of Fe2O3 has been modified,which has also been systematically studied.The study compares the surface structure and electrochemical properties of Fe2O3 material obtained by quenching and Fe2O3 material cooled naturally with the furnace.The results showed that quenching induced the formation of an amorphous activation layer on the surface of the Fe2O3 material,and XPS characterization verified the presence of oxygen vacancies on the surface.XRD and SEM tests also demonstrated a slight shrinkage of the lattice of the nano-spherical Fe2O3 material as a result of the quenching operation,with an overall smaller particle size than in the naturally cooled sample.The various modifying effects brought about by quenching resulted in a significant improvement in the electrochemical properties of Fe2O3 when used in Li-ion batteries.After 100 cycles at a current density of 0.5 A·g^-1 an extremely stable specific capacity was shown,which could be maintained at approximately 1000m Ah·g^-1.Further optimization experiments also explored the optimum quenching experimental conditions and it was found that the best electrochemical performance was obtained for samples quenched at 600°C and calcined for 5 h.To further address the volume effect of Fe2O3 when used in Li-ion batteries,atomic Ag doping was introduced using a co-deposition method to enhance the electrical conductivity of the composite before quenching.A series of SEM,TEM and EDX characterization techniques demonstrated the formation of a surface amorphous activation layer containing atomic Ag on the surface of the material.XPS and Raman spectroscopy verified the existence of electron exchange between Ag and Fe2O3 in the surface layer,which greatly enhanced the structural stability of the material.Electrochemical tests have shown that the lithium-ion batteries prepared from the composites exhibit little degradation during cycling after the introduction of Ag atom doping as compared to pure quenching operations.It continues to cycle up to 1000cycles with 1150.64 m Ah·g^-1 at a current density of 0.5 A·g^-1,and up to 1500 cycles with 528.30 m Ah·g^-1for cells cycled at a high current density of 5 A·g^-1 before decay.It also exhibits excellent electrochemical stability with a capacity retention rate of approximately 70%at the 2,000th cycle relative to the steady state.Given that this novel surface structure greatly improves the electrochemical properties of Fe2O3 materials;and that quenching is a simple and scalable research method that promises to be an enhanced modification for the next generation of solid-state electrodes for Li-ion batteries,this study further investigates the structural changes in the surface of Fe2O3 materials during quenching using an Ex-situ TEM technique.The results show that with increasing calcination temperature and time,the Fe2O3 nanoparticles undergo a transformation process from single crystal to polycrystalline to amorphous and from surface to internal structural changes.The subsequent quenching operation enables the nanoparticles to maintain their state at the end of the long calcination period,resulting in the formation of an amorphous surface activation layer.The study also characterized the physical features of the cycled composites by Ex-situ TEM and XPS techniques to investigate the reasons for the superb stability of their electrochemical properties.The results show that the quench-induced amorphous layer containing Ag atoms can maintain a dynamically stable state during repeated charging and discharging,allowing the overall structure of the composite nanospheres to remain stable and greatly mitigating the volume effect when Fe2O3 is applied to Li-ion batteries.