In Situ Visualized Cathode Electrolyte Interphase on LiCoO₂ in High Voltage Cycling

Abstract

Charging lithium ion battery cathode materials such as LiCoO to a higher voltage may simultaneously enhance the specific capacity and average operating voltage and thus improve the energy density. However, battery cycle life is compromised in high voltage cycling due to lattice instability and undesired oxidation of electrolyte. Cathode solid-electrolyte interphase (SEI), or cathode-electrolyte interphase (CEI), in situ formed at the cathode-electrolyte interface under high voltage, is critically important in understanding the cathode degradation process and crucial in improving high voltage cycle stability. Here we present in situ atomic force microscopy (AFM) investigation of CEI on LiCoO at high voltage. The formation of CEI is only observed at the LiCoO edge plane, not at the basal plane. The thin layer of AlO coating completely suppresses the formation of CEI at the edge planes, and is shown to significantly improve coin cell high voltage cycle stability.

Advances in Understanding Materials for Rechargeable Lithium Batteries by Atomic Force Microscopy

“…d) In situ AFM images of the CEI formation on the edge plane of LiCoO 2 crystal. Copyright 2017, American Chemical Society . AFM, atomic force microscopy; CEI, cathode electrolyte interphase; ESM, electrochemical strain microscopy.…”

“…No CEI can be observed on basal planes or edge planes with thin Al 2 O 3 coating on LiCoO 2 microcrystals. It is revealed that thin Al 2 O 3 coating can prevent the interfacial reaction, stabilize interface catalytic activity, and improve the high voltage stability of LiCoO 2 cathode . Wu et al.…”

“…interface catalytic activity, and improve the high voltage stability of LiCoO 2 cathode. [83] Wu et al use AM-FM and KPFM methods to investigate the surface morphology, contact stiffness, and surface potential distribution of LiCoO 2 thin film for deep understanding of the aging mechanism of LIBs. The film stiffness is related to the microstructure and elastic modulus of materials, inferring that the degradation is closely associated with the Li content reduction and CEI formation.…”

Functional Scanning Force Microscopy for Energy Nanodevices

“…Copyright 2001, Electrochemical Society. e,f) In situ AFM topographical image of basal plane of LiCoO 2 cathode before (e) and after (f) charging to 4.50 V. g,h) In situ AFM topographical image of edge plane of LiCoO 2 cathode before (g) and after (h) charging to 4.50 V. e–h) Reproduced with permission . Copyright 2017, American Chemical Society.…”

“…Especially when the sample was charged to 4.50 V, a fibrillary thin film covered the surface of the edge plane (Figure g,h). The formation of the CEI on edge planes can be completely suppressed by atomic layer deposited thin Al 2 O 3 layer, which was correlated with improved stability of coin cells in high voltage cycling …”