Impact Of P₂O₅ To TeO₂-V₂O₅ Glass On Structure And Electrochemical Properties

Disorder/order transition occurred in some oxide glasses when used as anode for lithium-ion batteries（Li Bs）,which enhanced its electrochemical performance.In this work,the effects of chemical composition of the TeO₂-V₂O₅-P₂O₅（TVP）glasses on microstructural and electrochemical properties was detailed investigated.The study emphasis is on the microstructural evolution of TVP glass anode upon the lithiation/delithiation process.Along with the redox reaction in discharge/charge progress,both the mechanisms for nanocrystal formation and its enhancement of electrochemical properties were clarified.In terms of phosphate glass is deliquescent,we studied the effects of humidity treatment at constant temperature on the microstructure of TVP glasses,in particular,the forms of water existing in glasses and its enhancement of the electrochemical performances.Thus the main research contents and conclusions are as follows:（1）We studied the effect of P₂O₅ in（70-x）TeO₂-30V₂O₅-x P₂O₅（TVP）glass anode on its microstructural and electrochemical properties.The results showed that both the glass transition temperature T_g and V⁴⁺content increased with the increasing P₂O₅.Based on the EIS analysis,the charge transfer resistance of Li Bs before cycles was reduced with the increasing V⁴⁺content.The TVP50（x=50 mol%）glass anode exhibits the largest discharge capacity of 220.7 m Ah g^-1 after 1000 discharge/charge cycles at the current density of 1000 m A g^-1.According to the NMR results,the TeO₃ and VO₄units in TVP glass gradually transformed into TeO₄ and VO₅ units with the increasing P₂O₅,promoting the formation of Li₂Te nanocrystals after cycles.Moreover,the Li₂Te increases with the increasing P₂O₅ content,which highly contributed to the increasement of the discharge capacity.（2）Taking the 30TeO₂-30V₂O₅-40P₂O₅（TVP40）glass with superior electrochemical performance as the research object,we conducted detailed investigations on its local structural evolution during discharge/charge cycles by means of the state-of-the-art solid-state nuclear magnetic resonance（SSNMR）in order to clarify the mechanism for nanocrystals formation and its enhancement for electrochemical performance.It was found that the structural network of TVP40 glass anode after cycles was fully broken into negatively charged species,such as[PO₄]^3-,[VO₄]^3-,[V₂O₇]^4-,[TeO₃]^2-and[Te₂O₅]^2-,which were bonded to Li⁺ions to form different types of nano-domains with a high degree of order.Combined the XRD,HRTEM and CV results,Li₃PO₄ and Li₂Te nanocrystals were confirmed to form in TVP40 glass anode after cycles.Both of them possess high ion conductivity.Besides,we acquired the diameter of Li₃PO₄ nanocrystal using the CT-DQ-DRENAR method.The coexistence of these different kind of nanocrystals prevented them from agglomerating.These nanocrystals with high ionic conductivity uniformly distributing in the glass matrix could effectively enhance the ion and electron transport of electrode and maintain the structure stable.Therefore,TVP40 glass anode gave Li Bs excellent performance.（3）We studied the effect of humidity treatment at constant temperature on the structural optimization of 20TeO₂-60V₂O₅-20P₂O₅ glass,and further studied its electrochemical performance when used as anode for Li Bs.It was found that with the increase of the relative humidity（RH）（to 65 RH%and 85 RH%）,H₄V₃P₃O_16.5·x H₂O precipitated along with the OH-group in glass matrix induced by the incorporated water.These OH-groups in 20TeO₂-60V₂O₅-20P₂O₅ glass can broaden the network channel for Li⁺diffusion,provide active sites for lithium storage,and enhance the electrical conductivity of anode.In addition,took 65RH sample as an example,the formation of nanocrystals featured with high specific surface area,thus enhanced the pseudocapacitance effect and improved its electrochemical performance.Notably,as a representative,the 65RH sample exhibits a reversible capacity of 442 m A h g^-1 and the capacity retention is nearly 100%at a current density of 1000 m A g^-1 after 200 cycles,which is much better than that of the TVP anode(182 m A h g^-1).The rational structure design by humidity treatment at constant temperature could enhance dramatically the capacity and cycling performance of the TVP glass.This study not only provides a promising pathway to efficiently improve the electrochemistry performance of the oxide glass electrode but also develops a new strategy to develop novel electrode materials for LIBs.The findings in this work provided important ideas for designing and developing high-performance glass anode materials for Li Bs.