Teresa Insinna

Lithium metal batteries (LMBs) show strong potential for next-generation energy storage, because of their high theoretical energy density. However, their practical deployment is limited by microstructure and dendrite formation, which raises serious safety and efficiency concerns. A key factor influencing dendrite growth is the passivating film, or solid electrolyte interphase (SEI), that forms at the lithium metal surface. Gaining insight into the SEI is essential for controlling dendrite formation, yet this remains challenging due to its complex composition and disorder. Lithium metal endogenous Dynamic Nuclear Polarization (DNP) offers opportunities to probe the SEI with enhanced sensitivity. In this work, we investigate how dendrite morphology influences both DNP enhancement and polarization transfer mechanisms. We develop a protocol to produce lithium dendrites with controlled morphologies on copper electrodes, and find that DNP efficiency is strongly affected by dendrite morphology and the substate they grow on, primarily through variations in the electron spin relaxation times. For Li dendrites grown on a copper substrate, extremely short relaxation times are seen for some morphologies, which we suggest is due largely to the Cu impurities present at the Li/SEI interface since the effect is more pronounced for the thin dendrites, where electrons travel for shorter distances before encountering a surface impurity. The enhancements also depend on the frequency of the applied microwave radio frequency (rf) irradiation, and the extent of rf penetration into the lithium microstructures. Finally, we explore polarization transfer from lithium metal to surrounding salt species in the SEI, providing insight into the underlying mechanisms.

Over the past 15 years, dynamic nuclear polarization (DNP) has emerged as a unique and powerful strategy to enhance the solid-state nuclear magnetic resonance (NMR) signals of surface species. This approach, known as DNP surface-enhanced NMR spectroscopy (DNP SENS), has been successfully applied to a broad range of functional materials. DNP SENS relies on the use of exogenous sources of electrons, typically stable organic radicals. A key method for adding these polarizing agents to the target material and obtaining high NMR signal enhancement factors is incipient wetness impregnation (IWI) with a radical-containing solution. However, DNP SENS via IWI is not amenable to all materials due to chemical incompatibilities between the polarizing solution and the surface of interest. This strongly limits the application fields of DNP-SENS. Here, we report the design and synthesis of new porous silica-based solids that incorporate organic biradicals within their bulk of their framework. These polarizing solids can be mixed with other powdered materials, and once impregnated with a pure solvent or solvent mixture, they efficiently transfer the polarization to external surfaces. Numerical simulations provide a framework to describe the 1H-spin diffusion-relayed polarization transfer from the polarizing solid to the target solid. This solid-to-solid relayed DNP approach is demonstrated with pristine and functionalized alumina particles, as well as sensitive catalytic surfaces. Substantial NMR sensitivity gains are reported on surface species, establishing a new strategy for DNP SENS.

Graphite is used, almost ubiquitously, as an anode material in today's high energy density Li-ion batteries. Both artificial and natural graphites are widely used, and there are large differences in the production methods, cost, particle morphologies, sizes, and percentage of defects in their structures, all these parameters affecting use and performance. The success of graphite as an anode depends on the formation of a Li-ion-conducting passivation layer (the solid electrolyte interphase (SEI)) on the first cycle, with the nature of this layer still being under investigation with a range of approaches. During lithiation (charge in a full cell), graphite is lithiated in stages and becomes electronically conductive. The conduction electrons of lithiated graphite anodes are exploited in this work to enhance the nuclear magnetic resonance (NMR) signal of bulk and surface nuclei via Overhauser dynamic nuclear polarization (DNP). The parameters directly affecting the enhancement factor (leakage factor, saturation factor, and coupling factor) are examined in detail for an artificial graphite at different lithiation stages. Four additional (natural and artificial) graphites are then studied to explore the effects of particle size and morphology, electron relaxation times, and conductivity on the observed DNP enhancements. Finally, the polarization transfer between bulk and surface (SEI) species is explored through ^6,7Li, ¹H, and ¹³C DNP NMR experiments.

Lithium imide is an underexplored candidate for an all-solid-state battery electrolyte. Here it is shown to possess many desirable properties and unusual electrochemical behaviour, alongside its first operation in two lithium metal batteries.

The increased capacity offered by oxygen-redox active cathode materials for rechargeable lithium- and sodium-ion batteries (LIBs and NIBs, respectively) offers a pathway to the next generation of high-gravimetric-capacity cathodes for use in devices, transportation and on the grid. Many of these materials, however, are plagued with voltage fade, voltage hysteresis and O₂ loss, the origins of which can be traced back to changes in their electronic and chemical structures on cycling. Developing a detailed understanding of these changes is critical to mitigating these cathodes' poor performance. In this work, we present an analysis of the redox mechanism of P2-Na_0.67[Mg_0.28Mn_0.72]O₂, a layered NIB cathode whose high capacity has previously been attributed to trapped O₂ molecules. We examine a variety of charge compensation scenarios, calculate their corresponding densities of states and spectroscopic properties, and systematically compare the results to experimental data: ²⁵Mg and ¹⁷O nuclear magnetic resonance (NMR) spectroscopy, operando X-band and ex situ high-frequency electron paramagnetic resonance (EPR), ex situ magnetometry, and O and Mn K-edge X-ray Absorption Spectroscopy (XAS) and X-ray Absorption Near Edge Spectroscopy (XANES). Via a process of elimination, we suggest that the mechanism for O redox in this material is dominated by a process that involves the formation of strongly antiferromagnetic, delocalized Mn-O states which form after Mg²⁺ migration at high voltages. Our results primarily rely on noninvasive techniques that are vital to understanding the electronic structure of metastable cycled cathode samples.

Graphite is the most commercially successful anode material for lithium (Li)-ion batteries: its low cost, low toxicity, and high abundance make it ideally suited for use in batteries for electronic devices, electrified transportation, and grid-based storage. The physical and electrochemical properties of graphite anodes have been thoroughly characterized. However, questions remain regarding their electronic structures and whether the electrons occupy localized states on Li, delocalized states on C, or an admixture of both. In this regard, electron paramagnetic resonance (EPR) spectroscopy is an invaluable tool for characterizing the electronic states generated during electrochemical cycling as it measures the properties of the unpaired electrons in lithiated graphites. In this work, ex situ variable-temperature (10-300 K), variable-frequency (9-441 GHz) EPR was carried out to extract the g tensors and line widths and understand the effect of metallicity on the observed EPR spectra of electrochemically lithiated graphites at four different states of lithiation. We show that the increased resolution offered by EPR at high frequencies (>300 GHz) enables up to three different electron environments of axial symmetry to be observed, revealing heterogeneity within the graphite particles and the presence of hyperfine coupling to Li nuclei. Importantly, our work demonstrates the power of EPR spectroscopy to investigate the local electronic structure of graphite at different lithiation stages, paving the way for this technique as a tool for screening and investigating novel materials for use in Li-ion batteries.

We report a novel magnetically-facilitated approach to produce 1-D ‘nano-necklace’ arrays composed of 0-D magnetic nanoparticles, which are assembled and coated with an oxide layer to produce semi-flexible core@shell type structures.

A series of triarylamines was synthesised and screened for their suitability as catholytes in redox flow batteries using cyclic voltammetry (CV). Tris(4‐aminophenyl)amine was found to be the strongest candidate. Solubility and initial electrochemical performance were promising; however, polymerisation was observed during electrochemical cycling leading to rapid capacity fade prescribed to a loss of accessible active material and the limitation of ion transport processes within the cell. A mixed electrolyte system of H₃PO₄ and HCl was found to inhibit polymerisation producing oligomers that consumed less active material reducing rates of degradation in the redox flow battery. Under these conditions Coulombic efficiency improved by over 4 %, the maximum number of cycles more than quadrupled and an additional theoretical capacity of 20 % was accessed. This paper is, to our knowledge, the first example of triarylamines as catholytes in all‐aqueous redox flow batteries and emphasises the impact supporting electrolytes can have on electrochemical performance.