Theoretical Study On Anchoring Effect Of Surface Modified Two-dimensional Materials In Lithium Sulfur Batteries

In recent years,with the increasing demand for portable electronic devices and electric vehicles,the development of electrochemical energy storage systems with higher energy density has become a trend.Lithium sulfur batteries stand out among the next generation of rechargeable lithium batteries due to their high theoretical capacity(1675 m Ahg^-1)and energy density(2600 Whkg^-1).However,the serious shuttle effect of polysulfides greatly hinders the practical application of lithium sulfur batteries.Due to the lack of effective means to suppress the shuttle effect,this has been a long-term problem hindering the development of lithium sulfur batteries.A large number of studies have focused on how to suppress the shuttle effect,such as reducing the solubility of electrolytes to polysulfides,introducing additives to the cathode,and adding solid electrolyte layers.Among them,the research on introducing two-dimensional cathode additives into the cathode of lithium sulfur batteries to suppress the shuttle effect has achieved great success.Importantly,two-dimensional materials have a large specific surface area and unique layered structure,and their unique electronic properties,good stability,and unique physical and chemical properties can effectively promote the electrochemical performance of batteries,reflecting excellent energy storage potential.For simple material system research,traditional theoretical research can provide better analytical expression and derivation methods,but if the system is relatively complex,it can often only be explored through the experience of researchers and repeated trial and error,which makes theoretical research often disconnected from experiments.In this context,Computational Materials Science as an interdisciplinary discipline between computer and materials science,and has been widely used in a short period of time due to its low cost,high accuracy,and short cycle characteristics.In this paper,the first principle calculation system is used to study whether two-dimensional electronic compounds Ca₂N,Y₂C and Ti₂O can effectively shuttle effect and improve battery performance as cathode anchoring materials of lithium sulfur battery.The detailed calculation contents are as follows:（1）Based on the structure of two-dimensional Y₂C,different functional groups（H,O,F,Cl and S）were used to modify its surface in theory,and their key properties as cathode anchoring materials for lithium-sulfur batteries were calculated using first-principles.The calculation results showed that Y₂CF₂ and Y₂CCl₂ have excellent adsorption energy and good adsorption structure,and have low Li⁺/S^2-diffusion barrier and Li₂S decomposition barrier,which meant that they can effectively inhibit the shuttle effect while also promoting the charge and discharge rate and electrochemical performance of the battery.So they completely meet the standard of ideal cathode anchoring material.（2）In theory,Ca₂NX_m（m=1,2）was constructed by modifying the surface of Ca₂N with X functional groups（H,O,F,Cl and S）.Through calculation,it was found that Ca₂NCl₂ has a large adsorption energy for polysulfides（2.96～4.02 e V）,and no obvious distortion was found in its adsorption structure,which indicated that it can effectively inhibit the shuttle of polysulfides.The decomposition barrier of Li₂S on its surface was much smaller than that of Li₂S under natural conditions and has a lower Li⁺/S^2-diffusion barrier.Various advantages show that Ca₂NCl₂ effect can become an excellent cathode anchoring material for lithium sulfur batteries.（3）In theory,six functional groups,O,F,Cl,S,N,and P,were introduced to modify the two-dimensional Ti₂O surface.Through simulation calculation,it was found that Ti₂OF₂ and Ti₂OS₂ have high adsorption energy and good anchoring performance,and their electrochemical properties were still stable after polysulfide adsorption,which indicated that it could not only effectively inhibit shuttle effect,but also improve the electrochemical performance of the battery.