Preparation And Li-storage Performance Of Perovskite-type High-entropy Oxide

Lithium ion battery is considered to be the most promising energy storage technology device,and has been widely concerned because of its excellent high specific energy,long cycle life and environmental protection.The disadvantages of high purity graphite,which is commonly used at present,such as low negative basic theoretical capacity and high volume utility of transition metal oxide anode materials in charge and discharge process limit the performance of lithium ion batteries.Therefore,this paper took perovskite type high-entropy oxides La(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O₃ as the research object,using unordered high entropy oxide（HEO）own high entropy stable crystal structure and lattice distortion effect between the principal and the"cocktail effect".The influence of preparation method and element substitution on its lithium storage performance was discussed,through the design of morphology structure and composition,so as to achieve the effect of"1+1>2".The specific research content and results of this paper are as follows:Firstly,porous perovskite type La(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O₃ HEO nano powder with granular aggregates was successfully prepared by solution combustion synthesis with metal nitrate as metal source and glycine as fuel,its specific surface area/aperture are 29.2 m²·g^-1/19.555 nm,and the surface oxygen vacancy content is40.07%.Studies show that the anode material shows good cyclic stability:with the increase of the number of cycles,the specific capacity decreases slightly at first and then increases gradually.Due to the high pseudocapacitance characteristic,the reversible specific capacity after 250 cycles is 300 m Ah·g^-1,and after 500 cycles,the reversible specific capacity increases to 570 m Ah·g^-1,which is not only much higher than its theoretical specific capacity(320 m Ah g^-1)and also higher than the binary perovskite La Co O₃ anode material(418 m Ah·g^-1)at the same current density.La(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O₃ HEO capacity increase attributed to the crystalline structure of configurational entropy of high stability,high constraint capacitance characteristic and the gradual improvement of electronic conductivity and Li⁺diffusivity.Then,using SiO₂ as templates,hollow spherical La(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O₃HEO with surface microporous was prepared by solution combustion synthesis and etching method,its specific surface area of 49.0 m²·g^-1 and oxygen vacancy is 53.53%.Electrochemical tests show that the hollow spherical La(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O₃showed excellent electrochemical performance under the current density of 200m A·g^-1,its first discharge specific capacity and coulombic efficiency are 716 m Ah·g^-1and 63.6%respectively,both higher than porous La(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O₃anode materials 50%,looping 250 times specific capacity increased to 1260 m Ah·g^-1.Moreover,the hollow spherical anode material exhibits better rate performance,with a specific capacity of 300 m Ah·g^-1 at a high current density of 3 A·g^-1.The further improvement in the electrochemical properties of hollow spherical La(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O₃ anode materials can be attributed to the increase in specific surface area increases the number of active sites and turns capacitance contribution rate;the increase of oxygen vacancy enhances electron transport performance.Finally,a series of La(Cr_0.2Fe_0.2Mn_0.2Ni_0.2Mg_xZn_0.2-x)O₃ HEO nanocrystalline powders with single perovskite structure were prepared by replacing expensive Co with Mg and Zn.Electrochemical performance studies show that:all the HEOs anode materials replaced by elements show good cycle stability and rate performance,among which Zn_0.15Mg_0.05 anode material has the highest first-cycle discharge capacity and coulomb efficiency（663 m Ah·g-1 and 57%）at 200 m A·g^-1,and the highest cycle capacity of 250 times.420 m Ah·g^-1.This is attributed to the barrier effect of appropriate amount of inactive Mg and li-Zn alloy formed by lithium of active Zn.