Probing microstructure of solid-state synthesized LiCoO₂ with MAS NMR spectroscopy

Area of Science:

• Materials Science
• Electrochemistry
• Solid-state Chemistry

Background:

• Lithium cobalt oxide (LiCoO2) is a key cathode material for lithium-ion batteries, valued for its high energy density and stable performance.
• Enhancing LiCoO2's charging voltage is crucial for maximizing its theoretical capacity.
• Understanding structure-property relationships at the atomic level is essential for optimizing LiCoO2.

Purpose of the Study:

• To investigate the local atomic environments in LiCoO2 synthesized using different sintering methods.
• To correlate the local atomic structure with electrochemical performance in all-solid-state batteries.
• To identify the optimal sintering method for improved LiCoO2-based battery performance.

Main Methods:

• High-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy (7Li and 59Co) was used to probe local atomic environments.
• Synthesis of LiCoO2 via three common sintering methods.
• Assembly and testing of all-solid-state lithium batteries using LiCoO2/LGPS/LiIn configuration.

Main Results:

• NMR analysis revealed distinct 7Li linewidths and relaxation times (T1) dependent on sintering method and lithium stoichiometry.
• The two-step sintering method was found to effectively eliminate unreacted Co3O4.
• LiCoO2 synthesized via the two-step method demonstrated the best discharge capacity in all-solid-state batteries.

Conclusions:

• The two-step sintering method yields LiCoO2 with improved purity and atomic ordering.
• NMR spectroscopy is a powerful tool for correlating local structure with electrochemical properties in LiCoO2.
• Optimizing sintering processes is critical for advancing the performance of LiCoO2-based all-solid-state batteries.