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Hau, Han-Ming

Publications and source records attributed to Hau, Han-Ming.

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Solvent Determines the Formation Pathway in Sol–Gel Synthesized Disordered Rock Salt Material for Lithium Ion Battery Application

The increasing demand for lithium-ion batteries with high capacity and cycling stability, in combination with the scarcity of cobalt and nickel, has led to significant efforts to develop new cathode materials based on earth-abundant transition metals. Mn- and Ti-based disordered rock salt (DRX) cathodes are promising candidates fulfilling these requirements. However, their large-scale fabrication can be energy- and time-intensive using traditional fabrication methods, e.g., solid-state synthesis. The present study showcases sol-gel synthesis as an alternative method with control over the crystallization pathway through solvent choice. Dimethylformamide (DMF) aids the homogenization of the transition metals during early crystallization stages and formation of Li2TiO3 and LiMn2O4 intermediates before the DRX phase is formed. In contrast, 2-methoxyethanol (2-ME) shows transition metal segregation and formation of an additional transition metal intermediate (Ti2MnO4) while not resulting in phase-pure DRX material after calcination. Coin cells prepared with DMF-material yield higher capacity and cycling stability compared with 2-ME material.

Kodalle, Tim↗
DOE OSTI2024

Earth-abundant Li-ion cathode materials with nanoengineered microstructures

Manganese-based materials have tremendous potential to become the next-generation lithium-ion cathode as they are Earth abundant, low cost and stable. Here we show how the mobility of manganese cations can be used to obtain a unique nanosized microstructure in large-particle-sized cathode materials with enhanced electrochemical properties. By combining atomic-resolution scanning transmission electron microscopy, four-dimensional scanning electron nanodiffraction and in situ X-ray diffraction, we show that when a partially delithiated, high-manganese-content, disordered rocksalt cathode is slightly heated, it forms a nanomosaic of partially ordered spinel domains of 3–7 nm in size, which impinge on each other at antiphase boundaries. The short coherence length of these domains removes the detrimental two-phase lithiation reaction present near 3 V in a regular spinel and turns it into a solid solution. This nanodomain structure enables good rate performance and delivers 200 mAh g –1 discharge capacity in a (partially) disordered material with an average primary particle size of ~5 µm. The work not only expands the synthesis strategies available for developing high-performance Earth-abundant manganese-based cathodes but also offers structural insights into the ability to nanoengineer spinel-like phases.

36 MATERIALS SCIENCE↗
DOE OSTI2023

In situ formed partially disordered phases as earth-abundant Mn-rich cathode materials

Abstract Earth-abundant cathode materials are urgently needed to enable scaling of the Li-ion industry to multiply terawatt hours of annual production, necessitating reconsideration of how good cathode materials can be obtained. Irreversible transition metal migration and phase transformations in Li-ion cathodes are typically believed to be detrimental because they may trigger voltage hysteresis, poor kinetics and capacity degradation. Here we challenge this conventional consensus by reporting an unusual phase transformation from disordered Li- and Mn-rich rock salts to a new phase (named δ ), which displays partial spinel-like ordering with short coherence length and exhibits high energy density and rate capability. Unlike other Mn-based cathodes, the δ phase exhibits almost no voltage fade upon cycling. We identify the driving force and kinetics of this in situ cathode formation and establish design guidelines for Li- and Mn-rich compositions that combine high energy density, high rate capability and good cyclability, thereby enabling Mn-based energy storage.

25 ENERGY STORAGE↗