Overdischarge-induced evolution of Cu dendrites and degradation of mechanical properties in lithium-ion batteries

The degradation of mechanical properties of overdischarge battery materials manifests as a significant effect on the energy density,safety,and cycle life of the batteries.However,establishing the correlation between depth of overdischarge and mechanical properties is still a significant challenge.Studying the correlation between depth of overdischarge and mechanical properties is of great significance to improving the energy density and the ability to resist abuse of the batteries.In this paper,the mechanical properties of the battery materials during the whole process of overdischarge from discharge to complete failure were studied.The effects of depth of overdischarge on the elastic modulus and hardness of the cathode of the battery,the tensile strength and the thermal shrinkage rate of the separator,and the performance of binder were investigated.The precipitation of Cu dendrites on the separator and cathode after dissolution of anode copper foil is a key factor affecting the performance of battery materials.The Cu dendrites attached to the cathode penetrate the separator,causing irreversible damage to the coating and base film of the separator,which leads to a sharp decline in the tensile strength,thermal shrinkage rate and other properties of the separator.In addition,the Cu dendrites wrapping the cathode active particles reduce the adhesion of the active particles binder.Meanwhile,the active particles are damaged,resulting in a significant decrease in the elastic modulus and hardness of the cathode.

TiS_(2)-graphene heterostructures enabling polysulfide anchoring and fast electrocatalyst for lithium-sulfur batteries:A first-principles calculation

Lithium-sulfur batteries have attracted attention because of their high energy density.However,the "shuttle effect" caused by the dissolving of polysulfide in the electrolyte has greatly hindered the widespread commercial use of lithiumsulfur batteries.In this paper,a novel two-dimensional TiS2/graphene heterostructure is theoretically designed as the anchoring material for lithium-sulfur batteries to suppress the shuttle effect.This heterostructure formed by the stacking of graphene and TiS2 monolayer is the van der Waals type,which retains the intrinsic metallic electronic structure of graphene and TiS2 monolayer.Graphene improves the electronic conductivity of the sulfur cathode,and the transferred electrons from graphene enhance the polarity of the TiS2 monolayer.Simulations of the polysulfide adsorption show that the TiS2/graphene hetero structure can maintain good metallic properties and the appropriate adsorption energies of 0.98-3.72 eV,which can effectively anchor polysulfides.Charge transfer analysis suggests that further enhancement of polarity is beneficial to reduce the high proportion of van der Waals(vdW) force in the adsorption energy,thereby further enhancing the anchoring ability.Low Li2 S decomposition barrier and Li-ion migration barrier imply that the heterostructure has the ability to catalyze fast electrochemical kinetic processes.Therefore,TiS2/graphene heterostructure could be an important candidate for ideal anchoring materials of lithium-sulfur batteries.