Preparation And Research Of High Entropy Oxide Anode Materials

The energy storage industry is multiplying in the current world,which serves as a possible solution for the emerging energy crisis.Advanced lithium-ion batteries have raised considerable research interest in recent studies due to their small volume,good stability,long service life,and rare pollution.Anode materials have been actively studied as an indispensable part of lithium-ion batteries.The developments of anode materials can improve lithium-ion batteries’charge/discharge capacity,and contribute to the scale-up application of lithium-ion batteries.A novel high entropy oxide（HEO）anode material,(Mg_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)O,was developed and characterized in this study.Specifically,micron-sized high entropy alloy particles were synthesized as precursors,which were transformed into HEO particles after heat treatment.The microstructural and electrochemical properties of HEO materials have been comprehensively investigated.The developed HEO anode material possesses a simple structure,high stability,and excellent electrochemical performance,which reveal promising applications in advanced lithium-ion batteries.This study is summarized in the following three parts.1.(Mg_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)O,the proposed HEO material,was prepared by hydrothermal route and systematically characterized.Specifically,five metal chlorides were dissolved at the same molar ratio in ethylene glycol solution and then treated at different hydrothermal temperatures.The HEO particles were obtained after the following heat-treatment process.The HEO materials prepared in proper hydrothermal parameters（i.e.,the volume ratio of water to ethylene glycol was 1:1）showed better cycle stability and electrochemical performance.The anode materials presented a good capacity reaching 174.7m Ah g^-1after 450 cycles,with a retention rate of 98.39%.The reversible discharge capacity of 240.1 m Ah g^-1indicated the good charge-discharge reversibility of the developed HEO anode material.2.(Mg_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)O was successfully fabricated via a homogeneous precipitation method,showing superior electrochemical performance and structural stability.The effect of magnesium content in HEO material on anode properties was comprehensively investigated.The results proved that single phase,rock salt type HEO materials were prepared under the designed ratios.As the incorporated Mg content increased,the high entropy alloy precursor particles changed from a stripe-shape to a rectangle-shape.When adding a proper concentration of Mg in the homogeneous solution（i.e.,1.5 times the standard ratio）,the prepared HEO anode materials possessed much-improved electrochemical performance.The charge/discharge capacity reached 947.6 m Ah g^-1at the current density of 200 m A g^-1,which remained stable after 500 cycles.Even at the high charge/discharge current density of 3000 m A g^-1,the reversible capacity of 110.9 m Ah g^-1was maintained.The magnesium oxide in the anode structure was inactive during the charging/discharging process,hindering the aggregation of other active components and maintaining the stability of microstructures during the charge/discharge process.3.(Mg_0.2Co_0.2Ni_0.2Cu_0.2Zn_0.2)O was prepared using the homogeneous precipitation method under different temperatures.The effect of precipitation temperatures on the HEO properties was comprehensively investigated.The HEO anode material prepared at 65℃had a better cycle performance among the tested samples.The charge/discharge capacity reached 1603.9 m Ah g^-1and remained stable at 477.9 m Ah g^-1after 290 cycles.This showed the excellent reversibility of prepared HEO anode materials.Cyclic voltammetric and impedance spectra showed that the HEO anodes prepared at 65℃had a faster lithium-ion diffusion rate.The results show that proper reaction temperature could improve the cyclic stability of high entropy oxide materials.