Design And Synthesis Of Zn₂GeO₄ Nanocomposite For Lithium Storage

Along with the development of the industrial revolution and the continuous consumption of non-renewable energy,the energy crisis is more and more critical.People gradually turn their attention to the use of renewable energy.However,due to the intermittent characteristics of renewable energy such as wind energy and solar energy,great energy storage equipment is needed to store the energy and then be used by people.With the large-scale application of portable electronics and new energy vehicles in modern society,the main commercial anode material of lithium ion battery is graphite,which is hard to meet the market's demand for high energy density batteries.Germanium based materials have higher electron conductivity and lithium ion diffusion rate than silicon and higher theoretical specific capacity than tin based materials,therefore,more research has been done by researchers.However,large volume changes of Ge elements during charging and discharging will lead to the rupture and reconstruction of SEI layer,resulting in low coulombic efficiency and poor cycle stability of batteries.Moreover,the high cost of material preparation has seriously hindered the commercial application of Ge-based materials.In order to solve these problems,researchers often combine germanium with other materials to make composite materials,so as to lower the cost of materials and enhance the electrochemical performance of materials.Among them,Ternary metal germanium oxide Zn₂Ge O₄ is considered as one of the most potential substitutes.Because Zn₂Ge O₄ material contains relatively cheap metal element Zn,and Ge only accounts for 27%of the total weight,so the cost of Ge-based negative electrode material can be reduced.Moreover,the presence of Zn can improve the reactivity of lithium during charging and discharging,thus improving the storage capacity of battery.In addition,the addition of electrochemically active Zn prevents materials such as Ge from accumulating into large particles during the cycling process,and acts as a buffer against volume changes and structural stresses.However,when Zn₂Ge O₄ is used as the anode material of lithium ion battery,the bulk expansion will occur,which reduces the electrochemical performance of the material.Therefore,this paper introduces the research progress of anode materials for lithium ion battery by reviewing three kinds of materials,silicon,germanium and tin base material.And on this basis,the anode materials of Zn₂Ge O₄ base for reasonable structural design,through methods such as doping,cladding,pore-forming modification of Zn₂Ge O₄ processing,effectively improve the electrical conductivity of Zn₂Ge O₄material,easing cycle in the process of volume expansion,preparation of superior electrochemical properties of the new type lithium ion battery anode composite materials.The main research contents are as follows:(1)Preparation of P-doped Zn₂Ge O₄@N-doped carbon nanorods and their electrochemical properties.Zn₂Ge O₄ nanorods were produced making use of C₄H₆O₄Zn and Ge O₂ as main raw materials by hydrothermal method.Subsequently,Zn₂Ge O₄@PDA nanorods were synthesized using dopamine hydrochloride as carbon source.Then,the porous P-Zn₂Ge O₄@NC composite material was formed by using sodium hypophosphate as the phosphorus source and high-temperature annealing treatment under nitrogen atmosphere.The porous P-Zn₂Ge O₄@NC composites exhibited excellent electrochemical performance by various morphology and structure characterization and electrochemical performance tests.This is because the nitrogen doped carbon and phosphorus structure improve the conductivity of the material,which makes the P-Zn₂Ge O₄@NC nanorods in the process of charging and discharging keep the stability of the structure and the SEI layer,behaved high specific capacity and great cycle stability and rate performance.After 140 cycles at a current density of 200 m A·g^-1,it still has a high capacity of854.4 m Ah·g^-1.(2)Preparation of porous Ge/Zn₂GeO₄@TiO₂@NC nanorods and study on their electrochemical properties.We synthesize the Zn₂Ge O₄@Ti O₂@PDA composite material with the Zn₂Ge O₄,tetramethyl titanate as the titanium source,and dopamine hydrochloric acid as the carbon source.The porous Ge/Zn₂GeO₄@TiO₂@NC nanorod composite material was prepared through the reduction treatment of high temperature hydrogen gas.The metallic Ge nanoparticles in the composite material can play a catalytic role,promote the reversible conversion reaction of active substances,and improve the reversible capacity of the material in the cycling process.The internal porous structure and the external Ti O₂ and N-doped carbon protective layer can effectively alleviate the volume expansion of the material during the process of deintercalation of lithium,maintain the structural stability of the material,and make the material show excellent cyclic stability and multiplication performance.At the current density of 1C(1443 m A·g^-1),after600 cycles,it still has 706.2 m Ah·g^-1 high reversible specific capacity with a capacity retention rate of up to 95.9%.