The Modifications Of Potassium Storage Property For The Bi₂S₃ Anode In Potassium-Ion Batteries

In recent years,global energy has been accelerating its transformation in the direction of high efficiency,cleanliness,and diversification,and its supply and demand pattern is entering a stage of profound adjustment.Promoting the energy revolution and focusing on the development of clean energy is an important task of my country’s 14th Five-Year Plan.Lithium-ion batteries（LIBs）,as a clean energy storage device,have many advantages such as high energy density,power density,and long-cycle stability.As the main power source for portable electronic devices,hybrid electric vehicles（HEVs）and electric vehicles（EVs）,it has achieved great success in commercial applications.In particular,the mass production of electric vehicles has brought important development opportunities for the LIBs industry.However,in the face of such a huge planning layout,the global lithium resource reserves will be far from meeting the needs of the market in the future.At the same time,the excessive exploitation and consumption of lithium resources will inevitably affect the ecological environment.The development of a potassium-ion battery（PIBs）system with similar chemical properties to LIBs and rich in resources,as a useful supplement to LIBs,is expected to be developed and applied in low-speed electric vehicles and large-scale energy storage.However,the large radius of potassium ions and the limited electrode reaction and diffusion kinetics in the battery hinder the practical progress of PIBs.Therefore,designing and developing high-performance electrode materials suitable for potassium ion storage is the key to the application and development of PIBs.Bismuth sulfide（Bi₂S₃）is a narrow band gap（～1.3 e V）semiconductor and has a high theoretical specific capacity based on the conversion-alloy mechanism in the electrochemical process,which is a potential high-performance PIBs anode material.However,this material has the problems of serious volume expansion and slow kinetics in the PIBs system,resulting in poor cycle stability and rate performance.In response to the above-mentioned scientific problems,this paper prepared bismuth sulfide with a microsphere structure and its composite materials,and studied its energy storage properties.The research conclusions obtained are as follows:First,we used the solvothermal method to prepare the Bi₂S₃ material with the second-level microsphere structure self-assembled by the first-level nanorods.By adjusting the particle size,the volume expansion of the electrode material during the electrochemical reaction is slowed down to improve its cycle stability;by adjusting the micron spherical morphology,the specific surface area of the material in contact with the electrolyte is increased,the diffusion path of potassium ions is shortened,and the rate performance is improved.We found that the concentration of the bismuth source greatly affects the particle size and morphology of the material,which in turn affects its electrochemical performance.Studies have shown that at the current densities of 0.2,0.5,1.0,1.5,and 2.0 A g^-1,Bi₂S₃-10 microspheres have reversible capacities of 570,480,340,270 and 230 m Ah g^-1,respectively.And the measured current density returns to 0.2 A g^-1,the specific capacity can still reach 545 m Ah g^-1.In contrast,Bi₂S₃-10micron spheres have excellent rate performance,while Bi₂S₃-5 micron spheres and Bi₂S₃-20 micron spheres have much inferior rate performance.Furthermore,the self-assembled Bi₂S₃ microspheres were coated with reduced graphene oxide by the visible-light-assisted method,and the Bi₂S₃@RGO composite material was successfully prepared.After testing,the composite material achieves a high specific capacity of 538 m Ah g^-1 after 10 cycles at a current density of 0.2 A g^-1,and the capacity retention rate can reach 72.7%.The capacity retention rate after 10cycles of the original material is only 63.4%.The material also exhibits excellent long-cycle performance and rate performance:at a current density of 2 A g^-1,the material can provide a specific potassium storage capacity of 237 m A h g^-1 for 300 cycles.In addition,the study on the potassium storage mechanism of Bi₂S₃@RGO found that during the first discharge,the potassium storage behavior was a combination of the conversion mechanism and the alloying reaction mechanism.Bi₂S₃@RGO composite material has such excellent electrochemical potassium storage performance thanks to:on the one hand,the synergy of conversion and alloying reaction not only helps to achieve high specific capacity,but also helps to alleviate the volume expansion of the material during the cycle.On the other hand,the introduction of a high-conductivity RGO network improves the dynamic performance of the material,and at the same time greatly alleviates the volume change of the material in the electrochemical reaction.Therefore,Bi₂S₃@RGO composite material has more remarkable long-cycle stability and rate performance.In this paper,we aimed at the volume expansion during the electrochemical potassium storage process the low intrinsic conductivity of the Bi₂S₃ anode material,from the perspective of material functional design,we adopt methods such as particle size optimization,shape control,and construction of conductive networks.It not only alleviates the volume expansion of the material during the cycle,but also effectively improves the dynamic properties of the electrode material,and the electrochemical performance is significantly improved.The research work in this paper provides practical experimental schemes and theoretical basis for the pioneering and development of PIBs anode materials.