Preparation Of Germanium-based Anode Materials And Their Lithium Storage Performance

With the rapid development of society,the existing commercial lithium-ion batteries have been difficult to meet the ever increasing demand due to their energy density.So it is urgent to develop lithium-ion batteries with higher energy density.In many studies about lithium-ion batteries,the development of high-capacity anode materials has demonstrate to be an effective method to improve the energy density of lithium-ion batteries.Germanium（Ge）-based materials have low working potential,high conductivity and high theoretical capacity,thus showing great potential in anode materials of lithium-ion battery.In general,the nanostructure and size of anode materials are intimately related to their electrochemical properties.In this work,we focused on the design and preparation of germanium-based nanomaterials.In the third chapter,we successfully realized the controllable preparation of unique Ge@C hollow nanostructures.In the fourth chapter,we developed a molten salt method to achieve the mild and efficient synthesis of Ge₄Se₉@C composites.Meanwhile,this work also investigated the lithium storage performance of the above two germanium-based anode materials.The main contents are as follows:1.A unique hollow structured Ge@C composite was designed and prepared,using commercial Ge O₂ as the germanium source and phenolic resin as the carbon source.The hollow Ge@C nanomaterials were successfully synthesized by carbonization and reduction under H₂/Ar atmosphere.The carbon skeleton provides the strong support for the nanostructure while providing channels for the transport of lithium ions and electrons,which enhances the overall electrical conductivity of the material.Ge nanoparticles are uniformly embedded in the carbon skeleton,which effectively buffers the volume expansion and maintains the structural integrity during charging and discharging.The Ge@C anode shows a high lithium storage performance with a reversible capacite of 1483 m Ah g^-1 at 200 m A g^-1,and good cycling stability retaining1100 m Ah g^-1 after 750 cycles at 1000 m A g^-1.2.A mild molten salt selenization method was developed to successfully prepare hollow Ge₄Se₉@C composite.The selenization of Ge@C was carried out in AlCl₃-Na Cl-KCl molten salt system at low-temperature using selenium powder as selenium source at 300℃.When molten salt was heated to the melting point,the system will maintain a stable liquid reaction environment.The whole synthesis process is green and non-toxic,which not only avoids excessive reaction temperature,but also achieves efficient synthesis with equal stoichiometric ratios.In addition,the unique hollow nanostructure of precursor is also maintained efficiently.The Ge₄Se₉@C anode exhibits excellent lithium storage performance,delivering a stable capacity of 830 m Ah g^-1 after 1000 cycles at 1000 m A g^-1,and achieves reversible phase transition during charging and discharging.Moreover,the full cell assembled with Ge₄Se₉@C and LiFePO₄ successfully achieves a high energy density of 327.1 Wh kg^-1.