Preparation Of Ge/GeO₂-based Anode Materials And Their Lithium Storage Performance

Due to their extended durability,reliable stability and eco-friendly nature,lithium-ion batteries have become increasingly prevalent in diverse industries.In the last few years,there has been a significant surge in demand for these batteries,primarily fuelled by the burgeoning consumer electronics and new energy vehicle markets.The traditional graphite cathode(theoretical specific capacity:372 mAh/g)can not satisfy the market requirements for lithium-ion batteries due to its limited energy density.Hence,the need of the hour is to create cathode materials for lithium-ion batteries that have a high energy density,are capable of enduring multiple cycles,and exhibit exceptional safety performance.Germanium has the potential to be an excellent anode material because of its high capacity,with a theoretical specific capacity that can be as high as 1625 mAh/g.Compared to conventional graphite,this material can provide four times the capacity,making it a highly promising choice for various applications.However,in the process of lithiation and de-lithiation,germanium undergoes a volume change of about 270%,which can lead to damage and fragmentation of the active material in repeated and continuous expansion and contraction,eventually leading to a rapid decrease in battery capacity and a rapid shortening of battery life.In order to improve the electrochemical performance and address the issue of volume expansion of germanium-based anode materials,this paper has developed nanomaterials made from germanium with varying structures.The main research results are as follows.(1)A honeycomb Ge/C composite with porous carbon skeleton covered with germanium nanoparticles was obtained by a one-step safe high-temperature assisted sol-gel method using inexpensive melamine foam as a carbon source.Specifically,the complex generated after the reaction of germanium dioxide with ethylenediamine was mixed with polyvinyl alcohol(PVA),after which it was monolithically attached to the melamine foam by means of the polymerization reaction between polyvinyl alcohol and melamine,and finally heat treated,and the structure and microscopic morphology were characterized by SEM and TEM,and it was observed that the germanium nanoparticles were uniformly embedded in the three-dimensional porous carbon skeleton.When the calcination temperature reached 800℃,researchers discovered that the material had an initial discharge capacity of 1255.6 mAh/g(100 mA/g).After undergoing 100 cycles,the material maintained a reversible capacity of 625.4 mAh/g and exhibited strong electrochemical performance.The porous carbon skeleton can suppress the volume expansion of germanium,improve the electrical conductivity of the material,and provide a proximity high-speed channel for ion/electron conduction.(2)Nanostructured GeO2 was prepared by a solvothermal method combined with high-temperature heat treatment in a simple,green and non-polluting process.Specifically,the precursor(NH4)3H(Ge7O16)H2O2.72 was firstly produced by hydrothermal reaction of germanium oxide and ammonia,and then calcined in a tube furnace to obtain nanostructured GeO2.compared with other fabricated materials and commercial GeO2 with larger size and irregular morphology,the GeO2-2 electrode exhibited excellent electrochemical performance.According to the research,the GeO2-2 electrode exhibited an initial discharge capacity of 1195.5 mAh/g(0.1 A/g).The electrode’s reversible capacity remained consistent at 811.0 mAh/g after 100 cycles,suggesting a capacity retention rate of 91.7%when compared to the second cycle.The use of nanostructure effectively retards the expansion of GeO2 volume during charge and discharge process,while also increasing the specific surface area.By extending the number of active sites that react and the contact area between the electrolyte and active material,the diffusion distance of lithium ions is reduced.This enhances the rate of electron transport,resulting in a higher reversible capacity and exceptional performance.(3)The hollow structured GeO2 nanoparticles were prepared by a simple and safe green bubble template solvothermal method in one step.Specifically,the hollow structured GeO2 nanoparticles were obtained by adding anhydrous ethylenediamine to create an alkaline environment,dissolving germanium oxide in deionized water,followed by the addition of sodium borohydride,a bubble template agent,and benzyl alcohol,a surfactant,through a hydrothermal reaction.The study discovered that the electrode that was made had a second discharge capacity of 545.3 mAh/g(0.1 A/g).In addition,the electrode demonstrated a consistent reversible capacity of 549.8 mAh/g following 100 charge and discharge cycles.Hollow-structured nanomaterials can withstand greater mechanical stresses due to their structural advantages and can effectively mitigate volume changes.In the meantime,the empty framework boasts an increased specific surface area that permits full percolation and infiltration of the electrolyte.Additionally,it provides a multitude of reactive locations for chemical reactions and expands the interaction zone between the active constituent and electrolyte.This leads to a reduction in the diffusion time of lithium ions and an acceleration in the transfer of electrons.