Preparation Of Multi-shelled Binary Metal Oxide Hollow Spheres As Electrode Materials For Battary

The electrode material is the key to improve energy density and power density of electrochemical energy storage device,especially,the power capability can be improved by designing the structure of electrode materials.Multi-shelled hollow structure material is an amazing material,especially,used as electrode material for battery,the multi-shelled hollow structure shows outstanding advantages as follows:a)The larger pores on the shell of hollow spheres ensure the electrolyte access to inner of hollow spheres,increasing the contacting area between active material and electrolyte as a result of the increase in storage sites,and this will improve the overall specific capacity of electrode at high current density;b)The thinner shell composed of nanoparticles around 20-40 nm significantly reduced diffusion path for both ions and electrons;c)The inner free volume of hollow structure between shells can alleviate expansion during insertion/extraction of Na+.Therefore,as electrode material,the multi-shelled hollow structure will provide excellent electrochemical performance.In this paper,the multi-shelled(Co2/3Mn1/3)(CO5/6Mn1/6)2O4 hollow sphere and Fe2(MoO4)3 hollow sphere were synthesized by an improved sequential templating method,and the effect of shell number on performance was explored.The specific work is shown as follow:Firstly,by controlling the precussor,adsorption temperature,adsorption time,the ratio of solution,and the crystalline rate of CoxMnyO4,the single to septuple-shelled(CO2/3Mn1/3)(CO5/6Mn1/6)2O4 hollow spheres was synthesized by sequential templating method.Excitingly,the multi-shelled(CO2/3Mn1/3)(CO5/6Mn1/6)2O4 hollow sphere possess uniform particle size,wrinkled surface,uniform pore size,larger surface area and pore volume.According to many characterization results,the material is spinel with Co3+/Co2+ of 2/1,Mn3+/Mn2+ of 1/1,Co2+/Mn2+ of 2/1,Co3+/Mn3+ of 5/1 which are coincidence with stoichiometric ratio of(CO2/3Mn1/3)(Co5/6Mn1/6)2O4,meanwhile,the Co and Mn are dispersed in(Co1/3Mn1/3)(Co1/6Mn1/6)2O4 hollow sphere uniformly.The effect of calcination condition on(Co2/3Mn1/3)(Co5/6Mn1/6)2O4 hollow sphere was explored;meanwhile,the effect of crystalline rate on(Co2/3Mn1/3)(Co5/6Mn1/6)2O4 hollow sphere was explored by adjusting the ratio of Mn into Co3O4,when the molar ratio of Co/Mn is 3.75,the crystalline rate is fastest,the septuple-shelled(Co2/3Mn1/3)(CO5/6Mn1/6)2O4 hollow sphere was obtained.As cathode material for alkaline battery,the multi-shelled(CO2/3Mni/3)(Co5/6Mni/6)2O4 hollow sphere show excellect electrochemical performance,compared to others,the septuple-shelled hollow sphere demonstrated an excellent specific capacity of 236.39 mAh g-1 at a current density of 1 A g-1 by three-electrode system(106.85 mAh g-1 at 0.5 A g-1 in alkaline rechargeable battery)and excellent cycling life(96.07%capacity retention after cycling 2000 time at 8 A g-1,84.17%capacity retention after cycling 3000 time at 1 A g-1 for alkaline rechargeable battery).As electrode materials for sodium battery,the hollow structure can relieve the expansion and shorten transferring path of sodium,therefore,we explore the effect on electrochemical performance of hollow structure in this section.Firstly,the citric acid can chelate the transition metal ion to restrict the hydrolysis of negative ion and positive ion as MoO42-and Fe3+,therefore,both MoO42-and Fe3+can be adsorped into carbon template,after calcination,the multi-shelled Fe2(MoO4)3 hollow sphere was synthesized.The mechanism was explored in detail.This method is not only fit for the preparation of multi-shelled Fe2(MoO4)3 hollow sphere,but also NiMoO4,MnMoO4 multi-shelled hollow sphere which is composed of metal ion and metal citric radical.Due the coarse surface,the free volume inside of structure,larger specific surface area of multi-shelled Fe(MoO4)3 hollow sphere,the electrolyte can diffuse to inside of hollow structure easily which provide more redox active site,and the transfer path of Na+ and electron are shorten,meanwhile,the expansion during charge/discharge can be released.Therefore,as electrode materials for sodium battery,the multi-shelled Fe2(MoO4)3 hollow sphere show excellent performance.Especially,the quintuple-shelled Fe2(MoO4)3 hollow sphere show highest specific capacity(99.03mAh/g),excellent stability(85.6mAh/g can be retained after 100 cycles at a current density of 2.2C),and outstanding rate capability(67.4 mAh/g can obtained at a current density 10C).I believe this work show an inspiration on multi-shelled hollow sphere,and preparation of excellent electrochemical materials.