Nanoscale Mapping of Transition Metal Ordering in Individual LiNi_0.5Mn_1.5O₄ Particles Using 4D-STEM

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Spinel LiNi0.5Mn1.5O4 is a high-voltage cathode material for lithium-ion batteries (LIBs).
• Electrochemical performance depends on transition metal arrangement (ordered vs. disordered structures).
• Current techniques lack the nanoscale resolution to study ordering within individual particles.

Purpose of the Study:

• To directly observe the ordering distribution of transition metals in LiNi0.5Mn1.5O4 particles.
• To develop a method for quantifying the local degree of ordering at the nanoscale.
• To understand how annealing conditions influence ordering and particle-scale distribution.

Main Methods:

• Utilized 4D-STEM (Scanning Transmission Electron Microscopy) for nanometric spatial resolution.
• Developed a quantification method based on electron diffraction spot intensities to determine the ratio of ordered to disordered spinel lattices.
• Analyzed the transition metal ordering distribution within individual LiNi0.5Mn1.5O4 particles.

Main Results:

• Achieved the first direct nanoscale observation of ordering distribution in individual LiNi0.5Mn1.5O4 particles.
• Demonstrated consistent transition metal ordering throughout primary particles in ordered spinel structures.
• Showed that the extent of ordering is influenced by particle-scale distribution and annealing conditions.
• Elucidated the boundaries between highly-ordered and low-ordered LiNi0.5Mn1.5O4 particles using 4D-STEM.

Conclusions:

• 4D-STEM provides unprecedented spatial resolution for studying cation ordering in battery materials.
• The degree of transition metal ordering significantly impacts LiNi0.5Mn1.5O4 particle characteristics.
• Annealing conditions play a critical role in controlling the nanoscale ordering and distribution within LiNi0.5Mn1.5O4 particles, affecting electrochemical performance.