Preparation Of Lithium Ferrite And Sodium Ion Battery Anode Materials By Combustion Method And Their Properties

The technology of Li-ion batteries(LIBs)is very mature and has been applied in various areas.In addition,sodium-ion batteries(SIBs)have been considered as a potential energy storage device in the future.Due to the stable structure and relatively mature preparation technology,graphite has been wildly applied as the commercial anode materials in LIBs.However,the low theoretical specific capacity(372 mAh g-1)of graphite is difficult to meet people's growing demands for high rate performance and high capacity of lithium ion batteries.On the other hand,the research of SIBs electrode materials is still at a developed stage.The drawbacks of carbon based materials with the most extensive studied anodes for SIBs are the low reversible capacities and not ideal initial coulombic efficiency.As a result,it is essential to exploit a new anode material with high capacity and low cost for the SIBs.Ferrite anode materials can react with multiple Li/Na ions per formula by a conversion reaction.In the electrochemical process all the oxidation states of ferrites are utilized,which provides a considerable specific capacity as the anode materials for LIBs.Compared with insertion SIBs anodes,which require particular material structure and interlayer spacing,ferrite anode materials can easier react with Na ions.However,the outstanding Li storage capabilities of ferrite anode materials are usually accompanied with a large volume change during charge/discharge processes,leading to the structural damages and pulverization of electrode material,which peel off easily from the current collector,resulting in a decreasing battery cycle life.Furthermore,in traditional ferrite preparation methods,long reaction time,or special instrumentation is necessary,which restricts the application of ferrites.Our study aims to solve the problems discussed as above,we have prepared MFe2O4(M=Zn,Co,Cu)as LIBs/SIBs anode materials with various morphologies and high crystallinity via using a facile,rapid and low-cost pathway through combustion synthesis.These electrochemical performances and morphologies were studied in detail.The innovation and achievements of our research can be summarized as follow:1.The presence of activity amino group in glycine,easily complexing metal ions,is more reactive fuel than citric acid,which is usually used as fuel in LIBs area.Hence,we used glycine as the fuel and complexing agent to prepare porous ZnFe2O4 and CoFe2O4 nanoparticles successfully via combustion method.The as-prepared materials possess porous network nanostructure which can not only ease the volume expansion during the charge/discharge processes but also provide more interstices for lithium ions insertion.What is more,the high crystallinity is able to stabilize the microstructure avoid the collapse after plenty of lithiation-delithiation processes.Electrochemical test results show that the first discharge capacity of ZnFe2O4 and CoFe2O4 are 1404.06 and 1258.6 mAh g-1 along with the related reversible capacities are 1021.7 mAh g-1 and 1041.8 mAh g-1,after 80 cycles at a current density of 200 mA g-1,respectively.The as-synthesized samples also exhibit outstanding rate capability and long cycle life.After 300 cycles at a high current density of 1000 mA g-1,the discharge capacity of ZnFe2O4 and CoFe2O4 are 794.7 mAh g-1 and 746.5 mAh g-1 with the capacity retention are 109.3%and 87.4%,compared with the second cycle there is almost no capacity fading.The results suggest that this method is a facile,effective and extensively used way to synthesize Fe-based binary transition metal oxides in porous spinel state as an anode material for lithium ion batteries with excellent electrochemical properties.The as-prepared materials show superior rate capability and cycling performance compared with the previous reports.In addition,ZnFe2O4 exhibits better performance than CoFe2O4 in all tests.2.After the first section research,we realize that the synthesis conditions can impact on the morphology,structure and lithium storage capacity of ZnFe2O4.In the comparison,the sample prepared at 700? possesses smaller grain size and lower agglomerated,which are beneficial to improve the performances in galvanostatic tests.As a result,700? is an appropriate calcining temperature for obtaining ZnFe2O4.Combining with the theoretical combustion equivalence ratio,the effects of different glycine-to-nitrate ratio on the combustion processes,phase composition,morphology and electrochemical performances of ZnFe2O4 are investigated in detail.As the glycine-to-nitrate molar ratio rises,the number of pores also increases,and the crystallinity of products first rises then falls.Fe2O3 as the impurity is generated in high glycine-to-nitrate molar ratio samples which affects the cycling stability of materials.When the glycine-to-nitrate molar ratio equals 1.0,the sample possesses less residual quantity of element C and N and more heat release in combustion reaction and it implies complete combustion which will lead to the better crystallinity and larger specific surface area.The electrochemical properties demonstrate that the sample exhibits a high initial discharge capacity of 1485.0 mAh g'1 and remains a stable reversible specific capacity of about 1195.3 mAh g-1 after 100 cycles.Moreover,it also manifests a superior high rate performance than that of other samples.As a result,we can get a conclusion that an appropriate glycine-to-nitrate molar ratio can obviously improve the performances of ZnFe2O4,when the ratio is 1.0,the pure ZnFe2O4 with uniform porous structure and excellent electrochemical performance is easily obtained.3.In this part the CuFe2O4 particles in cubic inverse spinel structure have been prepared for SIBs anode through combustion method with citric acid as a fuel and complexant for the first time.The Na storage electrochemical process of CuFe2O4 is also discussed.In the comparison experiment of calcination temperature,the results show that the 800? sample are not only possesses smaller lattice parameters and grain size,but also has abundant tiny particles,which lead to better storage sodium capacity than other samples.Combining with theoretical combustion equivalence ratio,we chose different citric acid-nitrate molar ratios and studied the effects on materials performances in depth.With the citric acid content increasing,both the particles agglomeration aggravates and the autoignition temperature rises.When the citric acid-nitrate molar ratio equals 0.56,the sample exhibits the best cycling stability,the specific capacity maintains about 311.8 mAh g-1 after 100 cycles at 50 mA g-1.It manifests superior high rate performance which recovers average discharge capacity to 413.4 mAh g-1 at 25 mA g-1 after 10 cycles at 2000 mA g-1.AC impedence spectra represent the sample possesses higher charge transfer ability,faster diffusion coefficient and lower interface impedance.As a result,when citric acid-nitrate molar ratio is 0.56,CuFe2O4 with excellent electrochemical performance SIBs anode can be obtained.