Controllable Fabrication Of Bimetallic Compound Hollow Heterostructures And Their Application In Lithium/Sodium Storage

Rechargeable batteries are key in the field of electrochemical energy storage,and the development of advanced electrode materials is essential to meet the increasing demand of electrochemical energy storage devices.Lithium-ion batteries（LIBs）currently provide the dominant power source for a range of devices,due to their high energy and power densities.Sodium-ion batteries（SIBs）are promising candidates for future large-scale energy storage systems due to their low cost and high safety.Related studies have shown that bimetallic compounds have better ion and electron transport capabilities than single-metallic compounds.At the same time,the construction of bimetallic compound heterostructures can lead to defects and heterogeneous electronic states at the phase interface,which leads to a substantial increase in material activity.In this thesis,we select bimetallic compound heterostructures as active materials to study their electrochemical performance as the anodes of lithium-ion battery and sodium-ion battery,respectively.The detailed contents are as follows:（1）Using ZIF-67 nanocubes as template,CoS₂@MnO₂ hollow nanoboxes with heterogeneous interfaces were prepared by PDA encapsulation,hydrothermal treatment and liquid phase vulcanization.The design shortens the diffusion path of electrons/Li⁺and enhances the electric conductivity of the compound.At the same time,the internal hollow structure provides abundant active sites for lithium absorption,and reduces the capacity loss caused by volume change in the process of charge and discharge.By virtue of these advantages,CoS₂@MnO₂ hollow nanoboxes show excellent electrochemical properties in terms of rate capability and cycle life.When the prepared CoS₂@MnO₂ hollow nanoboxes are used as the anode of LIBs,the first cycle charge/discharge capacity is 984.1/1433.8 mAh·g^-1.At the current density of 0.1A·g^-1,the capacity is 983.2 mAh·g^-1 after 200 cycles.（2）Using Fe-MIL-88A hexagonal rod as template,FeS₂@Mn S yolk-shell nanorods with heterogeneous interfaces were prepared by calcination,PDA encapsulation and gas phase vulcanization.An internal built-in electric field is generated at the interface of the heterostructure owing to differences in the bandgaps of the two compounds,and this is conducive to accelerating the Na⁺diffusion and enhancing charge transport.Meanwhile,the one-dimensional rod-like skeleton can effectively alleviate volume variations and prevent the aggregation of active material during the sodium storage process.As expected,the FeS₂@Mn S yolk-shell nanorods delivered good rate performance(561.4 mAh·g^-1 at 0.2 A·g^-1)and excellent cycling durability(86.4%capacity retention after 200 cycles at 0.2 A·g^-1 current density).In addition,at a high current density of 5 A·g^-1,the capacity was 338.8 mAh·g^-1 after the 600 cycles.