Design,Preparation And Potassium Storage Properties Of Bismuth Antimony Based High Entropy Metal Oxide Anode Materials

Potassium ion（K⁺）batteries are considered to be one of the important choices in the post-lithium-ion batteries era due to their low price and potentially high energy density.However,because of the large size of K⁺,the electrode material（especially the alloy anode electrode with high capacity and high density）has great volume change,slow diffusion kinetics and poor reversibility in the process of charging and discharging.These key problems seriously limit the research and development of potassium ion batteries and its key electrode materials.Due to the synergistic mechanism of entropy stability effect,multiple complementarity effect and lattice distortion effect,high entropy oxides can effectively alleviate the problems of large change in the anode electrode volume,poor structural stability and slow reaction kinetics of metal oxides in the process of charging and discharging.Therefore,in this thesis,a series of bismuth antimon-based high entropy metal oxides composed of five metal elements with equal molar ratio were prepared by ball milling with solid phase sintering and freeze-drying with solid phase sintering methods,and the effects of synthesis process,annealing temperature and composition on their morphology,structure,specific surface area and electrochemical potassium storage properties were fully studied.Multi-effect synergies such as entropy stability effect and nano size effect were used to effectively improve the reactivity and reversibility of active metal sites,improve the theoretical capacity,alleviate the impact of volume change on the electrode,and obtain excellent potassium storage performance.Specific research results are as follows:（1）High entropy metal oxide Bi Sb Co In Sn O_x（BM-BSCISO）was synthesized by ball milling and solid sintering,and the effects of sintering process on the morphology,structure and properties of the products were studied.The results show that the increase of entropy significantly increases the crystallization temperature of BM-BSCISO.When the annealing temperature is lower than 600℃,the product is close to amorphous structure,while the annealing temperature is higher than 700℃,the product is crystal structure.In addition,the five kinds of BM-BSCISO materials annealed at different temperatures all have large specific surface area and abundant mesoporous structure,but with the increase of sintering temperature,the primary particle size and mutual fusion degree increase,the specific surface area and pore volume decrease significantly.In summary,BM-BSCISO prepared at 500℃has large specific surface area and abundant mesoporous structure,which can effectively promote the infiltration of electrolyte,shorten the diffusion path of potassium ions,and effectively alleviate the volume change in the charge and discharge process,so as to show the optimal potassium storage performance.Under the current density of 100 m A g^-1,the capacity can still be maintained at323.5 m Ah g^-1 after 200 cycles,and the capacity retention rate is 84.1%.After 500 cycles of 500 m A g^-1,it can still maintain at 218.5 m Ah g^-1,and the capacity retention rate is 80.5%.The electrochemical performance of the above high entropy BM-BSCISO anode electrode is significantly better than that of the corresponding unit with low entropy and the reported bismuth antimony related metal oxide anode materials.（2）High entropy metal oxide Bi Sb Co In Sn O_x（FD-BSCISO）was prepared by freeze-drying and solid-phase sintering.XRD,XPS and element distribution test results show that FD-BSCISO and BM-BSCISO have similar crystal and electronic structure evolution processes.However,its morphology and potassium storage properties have changed obviously.FD-BSCISO nanoparticles are assembled into a typical layered porous structure,which is looser than that of BM-BSCISO.The electrochemical performance test indicates that FD-BSCISO-800 possesses the best potassium storage performance.After 200 cycles at 100 m A g^-1 current density,the capacity is 363.7 m Ah g^-1and the capacity retention rate is 96.1%.After 500 cycles at 500 m A g^-1,the capacity is 183.2 m Ah g^-1.At low current density,the potassium storage performance of FD-BSCISO-800 is slightly better than BM-BSCISO-500,but at high current density,due to the large particle size caused by sintering at high temperature,the solid phase diffusion distance of K⁺is significantly increased,and the rapid charge and discharge performance of FD-BSCISO-800 is slightly worse than BM-BSCISO-500.（3）Al³⁺,Fe³⁺and Cr³⁺were used to replace Sn⁴⁺in high entropy metal oxides Bi Sb Co In Sn O_x,and a series of bismuth antimony high entropy metal oxides were synthesized.XRD and SEM test results show that its morphology and structure are similar to that of bismuth antimony cobalt indium tin metal oxide.The materials prepared at 500℃and 800℃are amorphous and crystalline high entropy materials,respectively,but the crystal structure obtained at high temperature changes from hexagonal phase structure of bismuth antimony cobalt indium tin to typical cubic phase.The electrochemical performance test further shows that the prepared Bi Sb Co In Fe O_x high entropy oxide shows the best potassium storage performance.Bi Sb Co In Fe O_x-800 maintains 407.2 m Ah g^-1 capacity after 56 cycles under 100 m A g^-1,and 257.1 m Ah g^-1 capacity after 300 cycles under 500 m A g^-1current density,with almost no decline in capacity,showing superior long cycle potassium storage performance.