Study On Lithium Storage Properties Of Manganese-based Prussian Blue Analogues And Their Derivatives As Anode Materials For Lithium Ion Batteries

At present,commercial lithium-ion batteries(LIBs)with intercalation-type cathodes and graphite anodes are approaching their fundamental limits,mainly with respect to the specific capacities.In order to achieve the next generation of rechargeable LIBs with higher energy density,longer cycle life and better safety,it is necessary to develop advanced anode materials because they greatly affect these parameters,especially the capacity and working voltage of the battery.Among many anode materials,Prussian blue analogues(PBAs)have attracted extensive attention because of their open skeleton,adjustable components,simple preparation and non-toxic advantages.Among them,MnFe-PBA is considered to be a promising anode material for LIBs because of its high theoretical capacity and low cost.However,the conductivity of PBAs is low;And coordination water and zeolite water occupy a large number of lattice defects or vacancies in PBAs structure,which hinder the active sites of Li+ insertion reaction,resulting in inferior cycle stability and low capacity utilization.In view of the above problems of MnFe-PBA,we adopted the strategies of morphology regulation,element doping and calcination to further study PBAs and their derivatives with better electrochemical properties.The main research contents and results of this paper are as follows:(1)The controllable synthesis of MnFe-PBA with cubic morphology and properties of LIBs.MnFe-PBA precursor,named MnHFC,was synthesized by a simple coprecipitation method with MnSO4·H2O as metal source,K3Fe(CN)6 as ligand and PVP as binder.Because coordination water and zeolite water occupy a large number of lattice defects or vacancies,MnHFC as LIBs anode material shows low discharge capacity and short cycle life.In order to improve the electrochemical performance of MnHFC,we found that the performance of MnHFC-100 sample calcined at 100?in N2 atmosphere was significantly improved(288.7 mA h g-1 after 100 cycles at 100 mA g-1,which was 44.3%higher than that of MnHFC).Further study found that the structure of MnHFC-100 sample collapsed during repeated Li+(de-)insertion.In addition,the impedance of the electrode increases significantly after cycling.Therefore,the cycle stability of MnHFC-100 sample needs to be further improved.(2)The preparation of ternary metal ZnMnFe-PBA with truncated octahedron morphology and properties of LIBs.We used transition metal doping and low-temperature calcination activation methods to prepare ZnMnFe-PBA with unique truncated octahedral morphology and used it as LIBs anode material,showing excellent electrochemical performance.By exploring the effects of Zn-doping amount and calcination temperature on the morphology and electrochemical properties of MnFe-PBA and ZnMnFe-PBA,we found that Zn doping can improve the structural stability and electronic conductivity of the samples,which is conducive to the improvement of lithium storage performance.In addition,low temperature calcination increases the specific surface area of the sample,reduces[Fe(CN)6]vacancy in the sample,and makes the obtained Z10100 sample show high discharge capacity and good cycle stability.This work not only solves the problems of poor cycle stability and short life of PBA,but also provides a certain reference value for the synthesis of low-cost and efficient electrode materials.(3)The preparation of MnFe-PBA derived porous manganese-iron oxides-based hybrids and properties of LIBs.Using MnFe-PBA as template and organic carbon source,we prepared a series of manganese-iron oxides-based hybrids by calcination method,and explored the effects of the structure,composition and electrochemical properties of the products obtained at different calcination temperatures.Compared with other samples,the prepared porous Fe-Fe0.33Mn0.67O/C nanocube(named M600)shows the best rate performance and cycle life(?890 mA h g-1 at 0.1 A g-1,626.8 mA h g-1 after 1000 cycles at 1.0 A g-1 with a 99%capacity retention),which is mainly due to its unique pore structure and the synergy between components.Therefore,reasonable design of microstructure and composition of functional nanocomposites is the key to obtain ideal electrochemical properties.