Preparation Of High Entropy Rare Earth Oxide Powder And Research On Lithium Battery Properties

Nowadays,the energy revolution has put forward higher requirements for electrochemical energy storage technology,and secondary batteries are the key materials in the field of electrochemical energy storage.And new energy dominated by lithium battery is particularly concerned.However,the existing research results of electrochemical energy storage of traditional lithium ion batteries cannot meet the demands of high cycle and high capacity.So researchers have turned their efforts to developing new materials for lithium.As an emerging design concept,“high entropy”has been introduced into energy storage materials,which greatly expands the research scope of electrochemical energy storage materials.High entropy materials play a key role in the development of electrochemical properties.In this paper,a series of high and medium entropy oxides were synthesized by different preparation methods,and the formation of phase structure,optical and electrochemical properties were also studied.The research contents are as follows:（1）Multicomponent oxides(Ce_1/2Zr_1/2)_1-x(La_1/3Y_1/3Gd_1/3)_xO_2-σswere synthesized by precipitation method.XRD patterns analysis shows that the compostion with x=0.9 exhibits mixing crystal structure of fluorite and bixbyite phase,while the others possess single-phase fluorite structures.Transmission electron microscopy shows that nanoparticles of CZLYG90 with a particle size of about 34 nm were synthesized.Thermodynamic analysis shows that low mixing enthalpy and high configuration entropy are favorable to the stability of single-phase multiprincipal oxides.The Ultraviolet-visible absorption peak appears blue shift due to the decrease of interatomic forces.The direct band gap value of CZLYGx increases from 3.51 e V to 3.99 e V with x increasing.（2）(Y_0.2Sm_0.2La_0.2Gd_0.2Ce_0.2)₂Sn₂O₇ high entropy pyrochlore material was synthesized by solid phase method and precipitation method.The single-phase pyrochlorite structure was formed at 1300℃by the solid-phase method,and its average particle size was about 0.19μm.The optimum reaction condition of precipitation method was p H=10,and pure pyrochlorite phase was formed at1200℃.SEM showed that the powder had an average particle size of 0.15μm.According to the charge and discharge test analysis,the initial discharge specific capacity of the materials synthesized by solid-phase method was 677m A h g^-1.The precipitation method under the same test conditions has a first discharge specific capacity of 807 m A h g^-1,which is attributed to their smaller particle size.After 100 cycles,the two groups samples had a similar capacity of about 336 m A h g^-1.When the charge-discharge cycle with high current density of 2 A g^-1 is used,the sample prepared by solid-phase method has better rate performance with specific discharge capacity of 275 m A h g^-1.This is attributed to the agglomeration phenomenon of particles in the powder prepared by precipitation method,which leads to the reduction of cycle stability.Moreover,the analysis of AC impedance spectroscopy shows that the sample prepared by precipitation method has better conductivity,which further explains the phenomenon of high capacity of the sample prepared by precipitation method.（3）(Y_0.25Sm_0.25La_0.25Gd_0.25)₂Sn₂O₇ medium entropy pyrochlore material was synthesized by precipitation method and sintered at 700-1000℃,respectively.XRD patterns analysis shows that pyrochlorite structure is formed at 900℃,and the sintering temperature is lower than that of high entropy materials.This is due to the complexity of the elements and low configurational entropy.TEM results showed that nano-powder with particle size of about 45nm was synthesized.According to the charge and discharge test analysis,the initial discharge specific capacity of the medium entropy materials was 1151m A h g^-1,and the initial charge and discharge efficiency was 63.18%.Compared with the high entropy anode,the capacity of the medium entropy anode is increased by 344 m A h g^-1,which is attributed to the enhanced lithium ion diffusion rate by the nanopowder.The specific capacity can be maintained at about 351 m A h g^-1 after cycle 100 times.It is shown that the configurational entropy plays an important role in achieving a stable transformation reaction mechanism.At the same time,the medium entropy material has 332 m A h g^-1discharge specific capacity in the 2 A g^-1 large rate charge and discharge conditions.