TY - BOOK

T1 - Advancing understanding of disordered rocksalt material Li1.2Ni0.2Ti0.6O2 as a lithium-ion battery cathode

AU - McKinney, Sarah

PY - 2025

Y1 - 2025

N2 - Continued demand for energy storage systems with higher energy density and better cycle life means lithium-ion batteries (LIB) remain a key focus of research in the field. The cathode is the bottleneck component for improving these metrics in LIBs so new cathode materials continue to be studied. This thesis focuses on lithium transition metal oxide LIB cathode materials with disordered rocksalt (DRX) structure. Such materials have high theoretical capacities and allow the use of a diverse range of earth-abundant elements such as nickel and titanium. The solid-state synthesis of Li1.2Ni0.2Ti0.6O2, a member of the Li1+z/3Ni1/2-z/2Ti1/2+z/6O2 LNTO series, has been investigated. This Li-rich system has a theoretical capacity of 398 mAh g-1 based on lithium but only 133 mAh g-1 based on Ni2+/4+ redox which means it is expected to rely on oxygen redox to attain high capacity. Three different solid-state synthetic methods were developed to produce LNTO. The differences between the LNTO materials were investigated using X-ray diffraction, neutron diffraction and muon spectroscopy to understand their crystal structures while X-ray absorption spectroscopy, X-ray photoelectron spectroscopy and UV-Vis spectroscopy were used to understand charge distribution in the bulk and surface structures. A combination of ex situ and operando characterisation of the bulk and surface structures indicated that the material follows the asymmetric redox process caused by ligand-to-metal transfer (LMCT) demonstrated in the literature.Muon spectroscopy had not been previously used to characterise DRX materials and was a useful probe to show that particle size and morphology were the main difference between the LNTO materials, not their cation arrangements or differences in composition. The material with roughly 100 nm particle size synthesised using a lower temperature than the previous literature reports (850 °C) was found to show the best combination of specific capacity and capacity retention compared to the materials with 1 μm and 80 nm particle sizes.Developing this understanding of how to optimise particle size during synthesis rather than by adding an additional step to electrode fabrication contributes to efforts to commercialise DRX materials. Furthermore, this work highlights the advantages of using a non-electrochemical technique like muon spectroscopy to study ion diffusion in order to understand the effects of synthetic method.

AB - Continued demand for energy storage systems with higher energy density and better cycle life means lithium-ion batteries (LIB) remain a key focus of research in the field. The cathode is the bottleneck component for improving these metrics in LIBs so new cathode materials continue to be studied. This thesis focuses on lithium transition metal oxide LIB cathode materials with disordered rocksalt (DRX) structure. Such materials have high theoretical capacities and allow the use of a diverse range of earth-abundant elements such as nickel and titanium. The solid-state synthesis of Li1.2Ni0.2Ti0.6O2, a member of the Li1+z/3Ni1/2-z/2Ti1/2+z/6O2 LNTO series, has been investigated. This Li-rich system has a theoretical capacity of 398 mAh g-1 based on lithium but only 133 mAh g-1 based on Ni2+/4+ redox which means it is expected to rely on oxygen redox to attain high capacity. Three different solid-state synthetic methods were developed to produce LNTO. The differences between the LNTO materials were investigated using X-ray diffraction, neutron diffraction and muon spectroscopy to understand their crystal structures while X-ray absorption spectroscopy, X-ray photoelectron spectroscopy and UV-Vis spectroscopy were used to understand charge distribution in the bulk and surface structures. A combination of ex situ and operando characterisation of the bulk and surface structures indicated that the material follows the asymmetric redox process caused by ligand-to-metal transfer (LMCT) demonstrated in the literature.Muon spectroscopy had not been previously used to characterise DRX materials and was a useful probe to show that particle size and morphology were the main difference between the LNTO materials, not their cation arrangements or differences in composition. The material with roughly 100 nm particle size synthesised using a lower temperature than the previous literature reports (850 °C) was found to show the best combination of specific capacity and capacity retention compared to the materials with 1 μm and 80 nm particle sizes.Developing this understanding of how to optimise particle size during synthesis rather than by adding an additional step to electrode fabrication contributes to efforts to commercialise DRX materials. Furthermore, this work highlights the advantages of using a non-electrochemical technique like muon spectroscopy to study ion diffusion in order to understand the effects of synthetic method.

U2 - 10.17635/lancaster/thesis/2891

DO - 10.17635/lancaster/thesis/2891

M3 - Doctoral Thesis

PB - Lancaster University

ER -