Short-Range Order and Li_xTM_4-x Probability Maps for Disordered Rocksalt Cathodes.

Area of Science:

• Materials Science
• Computational Materials Science
• Solid-State Chemistry

Background:

• Short-range order (SRO) in cation-disordered states critically affects lithium-4 tetrahedron cluster formation in disordered rocksalt (DRX) cathode materials.
• Existing DRX materials exhibit lithium-4 probabilities below the random limit, with limited systematic investigation and strategies to surpass this threshold.
• Fundamental ordering behaviors on the face-centered cubic (FCC) lattice require deeper exploration.

Purpose of the Study:

• To quantitatively examine pair SRO parameters and lithium-x transition metal-4-x probabilities in disordered states.
• To investigate strategies for achieving lithium-4 probabilities exceeding the random limit.
• To advance the fundamental thermodynamic understanding of ordering behaviors in FCC systems.

Main Methods:

• Exhaustive Monte Carlo mapping across a simplified parameter space.
• Quantitative examination of pair SRO parameters.
• Analysis of lithium-x transition metal-4-x probabilities.

Main Results:

• In the disordered state, lithium-4 probability is governed by the nearest-neighbor (NN) pairwise SRO parameter.
• Lithium-4 probabilities do not simply attenuate low-temperature long-range order, especially in Layered and Spinel-like orderings.
• Proposed strategies can mitigate or reverse NN pair SRO mixing tendencies, enabling lithium-4 probabilities beyond the random limit.

Conclusions:

• Nearest-neighbor interactions are key determinants of short-range order and lithium-4 cluster formation in DRX materials.
• Strategies to control cation mixing can enhance lithium-4 probabilities, crucial for optimizing cathode performance.
• The findings offer a generalized thermodynamic framework for understanding ordering phenomena in FCC systems.