Molecular Dynamics Study On The Related Properties Of Solid Electrolyte LiPON And Anode Materials

As an efficient and environment-friendly modern energy storage device,lithium-ion batteries(LIBs)have played an important role in many fields.However,traditional LIBs still need further development.On the one hand,the theoretical specific capacity of traditional electrode materials is too low to satisfy future demands for high-capacity LIBs;on the other hand,traditional electrolytes have the risk of being flammable and leaking,which leads to potential safety hazards in LIBs.Recently,solid-state batteries(SSBs)have become research hotspots due to their advantages,such as high safety,high energy density,and simple battery structure,etc.However,the solid-solid interface problems between the electrode and the electrolyte,which have received widespread attention,seriously affect the performance of SSBs.Besides,finding high-capacity anode materials that match the solid electrolyte,in addition to the Li metal anode,is also an important subject.Aiming at the above problems,the studies on high-capacity amorphous silicon oxide(a-SiOy)anode materials and the interface problems of LiPON solid electrolytes are summarized as follow:1.We performed ReaxFF molecular dynamics(ReaxFF MD)simulations to examine the structural evolution,volume expansion,and diffusion properties in amorphous LixSiOy bulks,and to reveal the impact of oxygen content on its performance.Our results suggest that the inserted Li atoms preferentially disintegrate Si-Si connections in Si-rich oxide(a-SiO0.5),while they tend to break Si-O connections in O-rich silicon oxide(a-SiO).Besides,our study demonstrates that a higher concentration of O atoms in a-SiOy reduces its relative expansion upon lithiation,which is desirable for the application of electrode materials.However,we also find that the diffusion properties weaken with increasing O content.At the same level of O concentration,the diffusion coefficient of Li atoms(DLi)increases with lithiation,while at the same level of Li concentration,DLi decreases with the increasing of O content.2.We performed ab initio molecular dynamics(AIMD)to construct a-LiPON/Li(100)interface and Li2PO2N(100)/Li(100)interface.Our research demonstrates that atomic interdiffusion occurs in the interface area,forming a thin interface layer.The local structure statistics of the interface layers and LiPON bulk structure suggests that the proportion of tetrahedral structures centered on Li atom(Li[O2N2],Li[O3N],and Li[O4])decreases significantly,and the average coordination number of Li-O,Li-N,P-O,and P-N in the interface layers also decreases.Due to the changes of structure and coordination number in the interfaces,the ionic bonds between Li and O,N are weaker,and the obstacles of Li+diffusion are smaller in the interface layers.Compared with bulk LiPON electrolytes,the Li+conductivity in the interface layers is 2 to 3 orders of magnitude higher.