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Instruments / Technical Area	Publication Details	Published
I09-Surface and Interface Structural Analysis	Understanding the roles of tris(trimethylsilyl) phosphite (TMSPi) in LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811)/silicon–graphite (Si–Gr) lithium‐ion batteries Haidong Liu , Andrew Naylor , Ashok Sreekumar Menon , William R. Brant , Kristina Edström , Reza Younesi Advanced Materials Interfaces 8 DOI: 10.1002/admi.202000277 Diamond Proposal Number(s): [23159] Open Access Show Abstract ▼ Abstract: The coupling of nickel‐rich LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes with high‐capacity silicon–graphite (Si–Gr) anodes is one promising route to further increase the energy density of lithium‐ion batteries. Practically, however, the cycle life of such cells is seriously hindered due to continuous electrolyte degradation on the surfaces of both electrodes. In this study, tris(trimethylsilyl) phosphite (TMSPi) is introduced as an electrolyte additive to improve the electrochemical performance of the NMC811/Si–Gr full cells through formation of protective surface layers at the electrode/electrolyte interfaces. This is thought to prevent the surface fluorination of the active materials and enhance interfacial stability. Notably, TMSPi is shown to significantly reduce the overpotential and operando X‐ray diffraction (XRD) confirms that an irreversible “two‐phase” transition reaction caused by the formed adventitious Li2CO3 layer on the surface of NMC811 can transfer to a solid‐solution reaction mechanism with TMSPi‐added electrolyte. Moreover, influences of TMSPi on the cathode electrolyte interphase (CEI) on the NMC811 and solid electrolyte interphase (SEI) on the Si–Gr are systematically investigated by electron microscopy and synchrotron‐based X‐ray photoelectron spectroscopy which allows for the nondestructive depth‐profiling analysis of chemical compositions and oxidation states close to the electrode surfaces.	Jun 2020
I11-High Resolution Powder Diffraction	The influence of synthesis routes on the crystallography, morphology and electrochemistry of Li2MnO3 Ashok Sreekumar Menon , Dickson O. Ojwang , Tom Willhammar , Vanessa K. Peterson , Kristina Edstrom , Cesar Pay Gòmez , William R. Brant Acs Applied Materials & Interfaces DOI: 10.1021/acsami.9b20754 Diamond Proposal Number(s): [19093] Show Abstract ▼ Abstract: With the potential of delivering reversible capacities of up to 300 mAh/g, Li-rich transition metal oxides hold great promise as cathode materials for future Li-ion batteries. However, a cohesive synthesis-structure-electrochemistry relationship is still lacking for these materials, which impedes progress in the field. This work investigates how and why different synthesis routes, specifically solid-state and modified Pechini sol-gel methods, affect the properties of Li2MnO3, a compositionally simple member of this material system. Through a comprehensive investigation of the syn-thesis mechanism along with crystallographic, morphological and electrochemical characterization, the effects of different synthesis routes were found to predominantly influence the degree of stacking faults and particle morphology. That is, the modified Pechini method produced isotropic spherical particles with approx. 57% faulting and the solid state samples possessed heterogeneous morphology with approx. 43% faulting probability. Inevitably, these differences lead to variations in electrochemical performance. This study accentuates the importance of understanding how syn-thesis affects the electrochemistry of these materials, which is critical considering the crystallographic and electrochemical complexities of the class of materials more generally. The methodology employed here is extendable to studying synthesis-property relationships of other compositionally complex Li-rich layered oxide systems.	Jan 2020
I09-Surface and Interface Structural Analysis	Depth-dependent oxygen redox activity in lithium-rich layered oxide cathodes Andrew J. Naylor , Eszter Makkos , Julia Maibach , Niccolo Guerrini , Adam Sobkowiak , Erik Bjorklund , Juan G. Lozano , Ashok Sreekumar Menon , Reza Younesi , Matthew R. Roberts , Kristina Edström , M. Saiful Islam , Peter G. Bruce Journal Of Materials Chemistry A DOI: 10.1039/C9TA09019C Diamond Proposal Number(s): [14733, 16629] Open Access Show Abstract ▼ Abstract: Lithium-rich materials, such as Li1.2Ni0.2Mn0.6O2, exhibit capacities not limited by transition metal redox, through the reversible oxidation of oxide anions. Here we offer detailed insight into the degree of oxygen redox as a function of depth within the material as it is charged and cycled. Energy-tuned photoelectron spectroscopy is used as a powerful, yet highly sensitive technique to probe electronic states of oxygen and transition metals from the top few nanometers at the near-surface through to the bulk of the particles. Two discrete oxygen species are identified, On- and O2-, where n<2, confirming our previous model that oxidation generates localised hole states on O upon charging. This is in contrast to the oxygen redox inactive high voltage spinel LiNi0.5Mn1.5O4, for which no On- species is detected. The depth profile results demonstrate a concentration gradient exists for On- from the surface through to the bulk, indicating a preferential surface oxidation of the layered oxide particles. This is highly consistent with the already well-established core-shell model for such materials. Ab initio calculations reaffirm the electronic structure differences observed experimentally between the surface and bulk, while modelling of delithiated structures shows good agreement between experimental and calculated binding energies for On-.	Sep 2019

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