Sumaiyatul Ahsan

Advisor: Faisal M. Alamgir

 will propose a doctoral thesis entitled,

Designing stability from intrinsic instability: controlled structural and magnetic transitions in Ni-based oxides

On

[date & time] Session 1: Monday, November 17 at 11:00 AM ET (Teams Link)

[date & time] Session 2: Wednesday, November 19 at 2:00 PM ET (Teams Link)

[building & room] Location: MRDC 3515 Conference Room

Committee

Prof. Faisal M. Alamgir - School of Materials Science and Engineering (Advisor)

Prof. Aaron Stebner - School of Mechanical Engineering and School of Materials Science and Engineering

Prof. Hailong Chen - School of Mechanical Engineering and School of Materials Science and Engineering

Dr. Guoxiang (Emma) Hu - School of Materials Science and Engineering

Prof. Jie Xiao - School of Mechanical Engineering at University of Washington and Battelle Fellow at the Pacific Northwest National Laboratory 

Abstract:

Nickel-based oxides form the foundation of many high-energy batteries. While their layered structures enable high energy density, they also introduce structural and electronic instabilities that limit long-term performance. This dissertation will explore how these intrinsic instabilities, typically regarded to be detrimental to their functionality, can instead be controlled as design principles for new functions.

The first part of this study focuses on the formation of inert NiO in Ni-rich layered cathodes, which is widely viewed as a degradation mechanism for batteries. Here we leverage this seemingly undesirable phase to stabilize Ni-rich cathodes. Density functional theory (DFT) reveals a reduction in Ni 3d-O 2p hybridization in NiO compared to LiNiO2 (LNO), suggesting its potential as a protective layer. Guided by theory, we use the variable temperature X-ray diffraction (VT-XRD) to identify optimal conditions for introducing oxygen vacancy on the surface of LiNi0.8Mn0.1Co0.1O2 (NMC811), which triggers a phase transformation from layered to rock salt NiO on the surface creating a core-shell structure as evidenced by X-ray photoelectron spectroscopy (XPS). Electrochemical methods such as constant current long-term cycling, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) reveal improved capacity, higher Li+ diffusivity, and lower resistance during cycling. X-ray absorption spectroscopy (XAS) and scanning transmission electron microscopy (STEM) imaging confirms reduced disorder and structural heterogeneity. By reframing surface NiO as a controllable design principle, we offer a materials-intrinsic, scalable route to extend the durability of Ni-rich cathodes.

The second part of this thesis further challenges the conventional view that NiO is electrochemically inert and extends the use of lithium-insertion in NiO to magnetic and electrochromic applications. During Li-insertion in NiO electrode, the electrode undergoes a reversible conversion reaction to form Li2O and metallic nickel as evidenced by CV. We demonstrate that this reaction can reversibly switch the magnetic property of NiO between antiferromagnetic NiO and ferro/ferrimagnetic Ni states, as confirmed by the superconducting quantum interference device (SQUID). XRD and scanning electron microscope (SEM) showed the presence of nano-sized Ni particles, which resulted in a high temperature superparamagnetic transition.  Furthermore, the ultraviolet-visible (UV-Vis) spectroscopy reveals reversible bandgap modulation between wide-bandgap NiO and metallic Ni by Li+ insertion, extending NiO’s relevance to optical switching applications.

The final portion of this study integrates defect analysis and magnetic measurements to probe the temperature-dependent structural evolution of LiNiO2 (LNO), a material whose crystallographic symmetry remains a subject of longstanding debate due to minimal structural changes compared to isostructural NaNiO2 across temperature and the pervasive influence of intrinsic defects. Decoupling these subtle structural changes from antisite disorder and NiO inclusions has remained an open challenge. Because both the variable temperature nuclear magnetic resonance (VT-NMR) and SQUID measurements are sensitive to minor defect populations during phase transitions, these experimental approaches will be combined with ab initio molecular dynamics (AIMD) simulations to disentangle these phenomena. This integrated approach will provide new insight into structural evolution of LNO which will extend our understanding of its charge compensation mechanism.

Together, these investigations integrate bulk (XRD), surface (XPS), and temperature-dependent (VT-NMR, VT-XRD) probes with element-specific (XAS, XES), microscopic (SEM, STEM), magnetic (SQUID), and optical (UV-Vis) analyses. Complementary DFT and AIMD simulations elucidate the thermodynamic and kinetic origins of the observed transitions. This multimodal framework provides new insight into how lattice, spin, and charge instabilities can be harnessed to design multifunctional, durable Ni-based oxides for energy storage, magnetic and optical applications.