Construction And Research On Lithium Battery Properties Of Poms-based Ionic Crystals

With the rapid growth of global energy demand,the development of clean energy and the realization of sustainable development of energy utilization are urgent problems to be solved in the field of energy storage.Lithium-ion batteries（LIBs）have become the most promising energy storage systems because of the high energy density.However,the lack of low-potential and high-capacity anode materials limits the further improvement of Li-ion battery performance.In consequence,the development of high-efficiency new anode materials is crucial for promoting energy development.In this paper,a series of POMs-based ionic crystals（PICs）have been constructed by utilizing POMs with unique advantages such as redox reversibility,multi-electron transfer characteristics and counterbalancing cation tunability.It makes up for the defects of easy agglomeration and loss of POMs in practical applications,realizes the uniform distribution of POMs,improves the rate of charge transfer and lithium-ion migration,and exhibits excellent lithium storage performance.In addition,the composition-structure-function connection has been elucidated.The importance of the synergistic mechanism of anion and cation in PICs and pore structure for lithium storage has been revealed.The designability of PICs opens up new ideas for the development of new anode materials for lithium-ion batteries.The specific work is as follows:1.A series of inorganic cationic POMs-based ionic crystals with transition metal ions as reverse cations have been successfully constructed by cation exchange method.:Fe PMo₁₂O₄₀、Co_1.5PMo₁₂O₄₀、Ni_1.5PMo₁₂O₄₀.The good lithium storage performance has been obtained with solving the problem of easy agglomeration and loss of POMs.It is confirmed that PICs are more prone to redox reaction because the introduction of transition metal cations increases the electron cloud density of[PMo₁₂O₄₀]^3-.Furthermore,It is revealed that the synergistic mechanism of anions and cations accelerates electron transport and greatly affects the lithium storage performance.The specific capacity of Fe PMo₁₂O₄₀can still maintain 872.4 m A h g^-1 at the current density of 0.5 A g^-1after 100 cycles,showing excellent cycling and rate performance2.Compared with inorganic cations,the structure and composition of metal complex cations are more diverse.In addition,the PICs formed by the combination of metal complex cations and POMs anions usually have pore structures.Therefore,on the basis of the work in the previous chapter,in order to explore the influence of counter cations on the lithium storage performance of POMs in more detail,a series of trinuclear metal complex-type of POMs-based ionic crystals were successfully constructed by precisely controlling the content of metal centers in the metal complex cations.The accurate structure of PICs has been determined,which expands the application of PICs in the field of lithium-ion battery.The structure-activity relationship of PICs as anode materials in the process of lithium storage has been elucidated.In addition,it is revealed that the synergistic mechanism of anion and cation in PICs and the pore structure are the keys to improve the lithium storage performance of PICs.Under the same conditions,the lithium storage performance of PICs（PIC（I）,PIC（II）,PIC（III））with the ratio of 2:1 cation and anion is much higher than that of each component of cation and anion and physical mixture,which proves that the formation of PICs greatly improves the lithium storage performance.Furthermore,the three kinds of POMs-based ionic crystals have different pore structures because of different effects of electrostatic interactions and hydrogen bonding by precisely regulating of metal center content.The construction of the pore structure create conditions for accelerating electron transfer and Li⁺diffusion.Therefore,PIC（II）has the best specific capacity,reaching 1142 m A h g^-1 under the current density of 100m A g^-1.