Additive stabilization of SEI on graphite observed using cryo-electron microscopy

Bing Han,Yucheng Zou,Jing Wu,Yunxian Qian,Shiguang Hu,Guiyin Xu,Yuanyuan Kang,Meng Gu,Xiaomin Ma,Tengteng Li,Hong Wang,Yonghong Deng,Hong Meng,Jianquan Yao,Zhen Zhang,Ju Li

doi:10.1039/d1ee01678d

Abstract

Cryo-electron microscopy study finds that EC-based electrolyte can exfoliate the graphite surface and destabilize the SEI. Useful additives including FEC, DTD, TPP, and VC can form a stable SEI to protect the graphite anode.

Highlights

Graphite is the prevalent commercial anode for rechargeable Li-ion batteries in electric vehicles and consumer electronics
A large degree of graphite layer expansion has been observed due to the Li(PC)x intercalation into the graphite as shown by the schematic in Fig. S2-a (ESI†),[7] where Li(PC)x stands for a Li+(PC)x cation complex with an electron attracted to the metallic graphene layers nearby, where x may be smaller than y as this cation may shed some solvent molecules as it inserts in between the graphene
For any x Z 1, such process will be harmful to the long-term cycling stability of the graphite anode, as the expanded c-spacing and residual stress due to the solvent molecule lead to the exfoliation of the graphene layers or chunks of graphite

Summary

Introduction

Graphite is the prevalent commercial anode for rechargeable Li-ion batteries in electric vehicles and consumer electronics. DTD has a higher reduction potential (1.3 V versus Li+/Li metal) than EC (0.95 V),[8] which means that DTD is easier to be reduced at the graphite anode surface to form SEI, which blocks the entry of the Li-electrolyte solvation sheath complex and only allows naked Li+ ion to transport across it.

Results

Conclusion