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Instruments / Technical Area	Publication Details	Published
I09-Surface and Interface Structural Analysis	Surface chemistry dependence on aluminum doping in Ni-rich LiNi0.8Co0.2−yAlyO2 cathodes Zachary W. Lebens-higgins , David M. Halat , Nicholas V. Faenza , Matthew J. Wahila , Manfred Mascheck , Tomas Wiell , Susanna K. Eriksson , Paul Palmgren , Jose Rodriguez , Fadwa Badway , Nathalie Pereira , Glenn G. Amatucci , Tien-lin Lee , Clare P. Grey , Louis F. J. Piper Scientific Reports 9 DOI: 10.1038/s41598-019-53932-6 Diamond Proposal Number(s): [22250, 22148] Open Access Show Abstract ▼ Abstract: Aluminum is a common dopant across oxide cathodes for improving the bulk and cathode-electrolyte interface (CEI) stability. Aluminum in the bulk is known to enhance structural and thermal stability, yet the exact influence of aluminum at the CEI remains unclear. To address this, we utilized a combination of X-ray photoelectron and absorption spectroscopy to identify aluminum surface environments and extent of transition metal reduction for Ni-rich LiNi0.8Co0.2−yAlyO2 (0%, 5%, or 20% Al) layered oxide cathodes tested at 4.75 V under thermal stress (60 °C). For these tests, we compared the conventional LiPF6 salt with the more thermally stable LiBF4 salt. The CEI layers are inherently different between these two electrolyte salts, particularly for the highest level of Al-doping (20%) where a thicker (thinner) CEI layer is found for LiPF6 (LiBF4). Focusing on the aluminum environment, we reveal the type of surface aluminum species are dependent on the electrolyte salt, as Al-O-F- and Al-F-like species form when using LiPF6 and LiBF4, respectively. In both cases, we find cathode-electrolyte reactions drive the formation of a protective Al-F-like barrier at the CEI in Al-doped oxide cathodes.	Dec 2019
I09-Surface and Interface Structural Analysis	Resonant doping for high mobility transparent conductors: the case of Mo-doped In2O3 Jack E. N. Swallow , Benjamin A. D. Williamson , Sanjayan Sathasivam , Max Birkett , Thomas J. Featherstone , Philip A. E. Murgatroyd , Holly J. Edwards , Zachary W. Lebens-higgins , David A. Duncan , Mark Farnworth , Paul Warren , Nianhua Peng , Tien-lin Lee , Louis F. J. Piper , Anna Regoutz , Claire J. Carmalt , Ivan P. Parkin , Vin R. Dhanak , David O. Scanlon , Tim D. Veal Materials Horizons 6 DOI: 10.1039/C9MH01014A Diamond Proposal Number(s): [18428] Open Access Show Abstract ▼ Abstract: Transparent conductors are a vital component of smartphones, touch-enabled displays, low emissivity windows and thin film photovoltaics. Tin-doped In2O3 (ITO) dominates the transparent conductive films market, accounting for the majority of the current multi-billion dollar annual global sales. Due to the high cost of indium, however, alternatives to ITO have been sought but have inferior properties. Here we demonstrate that molybdenum-doped In2O3 (IMO) has higher mobility and therefore higher conductivity than ITO with the same carrier density. This also results in IMO having increased infrared transparency compared to ITO of the same conductivity. These properties enable current performance to be achieved using thinner films, reducing the amount of indium required and raw material costs by half. The enhanced doping behavior arises from Mo 4d donor states being resonant high in the conduction band and negligibly perturbing the host conduction band minimum, in contrast to the adverse perturbation caused by Sn 5s dopant states. This new understanding will enable better and cheaper TCOs based on both In2O3 and other metal oxides.	Sep 2019
I09-Surface and Interface Structural Analysis	Band edge evolution of transparent Zn M 2 I I I O 4 ( M I I I = Co , Rh, Ir) spinels Matthew Wahila , Zachary W. Lebens-higgins , Adam J. Jackson , David O. Scanlon , Tien-lin Lee , Jiaye Zhang , Kelvin H. L. Zhang , Louis F. J. Piper Physical Review B 100 DOI: 10.1103/PhysRevB.100.085126 Diamond Proposal Number(s): [16005] Show Abstract ▼ Abstract: Zn M I I I 2 O 4 ( M I I I = Co , Rh, Ir) spinels have been recently identified as promising p -type semiconductors for transparent electronics. However, discrepancies exist in the literature regarding their fundamental optoelectronic properties. In this paper, the electronic structures of these spinels are directly investigated using soft/hard x-ray photoelectron and x-ray absorption spectroscopies in conjunction with density functional theory calculations. In contrast to previous results, ZnCo 2 O 4 is found to have a small electronic band gap with forbidden optical transitions between the true band edges, allowing for both bipolar doping and high optical transparency. Furthermore, increased d − d splitting combined with a concomitant lowering of Zn s / p conduction states is found to result in a ZnCo 2 O 4 ( ZCO ) < ZnRh 2 O 4 ( ZRO ) ≈ ZnIr 2 O 4 ( ZIO ) band gap trend, finally resolving long-standing discrepancies in the literature.	Aug 2019
I09-Surface and Interface Structural Analysis	Revisiting the charge compensation mechanisms in LiNi 0.8 Co 0.2−y Al y O 2 systems Zachary W. Lebens-higgins , Nicholas V. Faenza , Maxwell D. Radin , Hao Liu , Shawn Sallis , Jatinkumar Rana , Julija Vinckeviciute , Philip J. Reeves , Mateusz Zuba , Fadwa Badway , Nathalie Pereira , Karena W. Chapman , Tien-lin Lee , Tianpin Wu , Clare P. Grey , Brent Melot , Anton Van Der Ven , Glenn G. Amatucci , Wanli Yang , Louis F. J. Piper Materials Horizons 5 DOI: 10.1039/C9MH00765B Diamond Proposal Number(s): [19162] Open Access Show Abstract ▼ Abstract: Oxygen participation, arising from increased transition metal–oxygen covalency during delithiation, is considered essential for the description of charge compensation in conventional layered oxides. The advent of high-resolution mapping of the O K-edge resonant inelastic X-ray scattering (RIXS) provides an opportunity to revisit the onset and extent of oxygen participation. Combining RIXS with an array of structural and electronic probes for the family of Ni-rich LiNi0.8Co0.2−yAlyO2 cathodes, we identify common charge compensation regimes that are assigned to formal transition metal redox (<4.25 V) and oxygen participation through covalency (>4.25 V). From O K-edge RIXS maps, we find the emergence of a sharp RIXS feature in these systems when approaching full delithiation, which has previously been associated with lattice oxidized oxygen in alkali-rich systems. The lack of transition metal redox signatures and strong covalency at these high degrees of delithiation suggest this RIXS feature is similarly attributed to lattice oxygen charge compensation as in the alkali-rich systems. The RIXS feature's evolution with state of charge in conventional layered oxides is evidence that this feature reflects the depopulation of occupied O 2p states associated with oxygen participation.	Jul 2019
I09-Surface and Interface Structural Analysis	Evolution of the electrode-electrolyte interface of LiNi 0.8 Co 0.15 Al 0.05 O 2 electrodes due to electrochemical and thermal stress Zachary W. Lebens-higgins , Shawn Sallis , Nicholas V. Faenza , Fadwa Badway , Nathalie Pereira , David M. Halat , Matthew Wahila , Christoph Schlueter , Tien-lin Lee , Wanli Yang , Clare P. Grey , Glenn G. Amatucci , Louis F. J. Piper Chemistry Of Materials DOI: 10.1021/acs.chemmater.7b04782 Diamond Proposal Number(s): [12764, 16005] Show Abstract ▼ Abstract: For layered oxide cathodes, impedance growth and capacity fade related to reactions at the cathode-electrolyte interface (CEI) are particularly prevalent at high voltage and high temperatures. At a minimum, the CEI layer consists of Li2CO3, LiF, reduced (relative to the bulk) metal-ion species, and salt decomposition species but conflicting reports exist regarding their progression during (dis)charging. Utilizing transport measurements in combination with x-ray and nuclear magnetic resonance spectroscopy techniques, we study the evolution of these CEI species as a function of electrochemical and thermal stress for LiNi0.8Co0.15Al0.05O2 (NCA) particle electrodes using a LiPF6 ethylene carbonate: dimethyl carbonate (1:1 volume ratio) electrolyte. Although initial surface metal reduction does correlate with surface Li2CO3 and LiF, these species are found to decompose upon charging and are absent above 4.25 V. While there is trace LiPF6 breakdown at room temperature above 4.25 V, thermal aggravation is found to strongly promote salt breakdown and contributes to surface degradation even at lower voltages (4.1 V). An interesting finding of our work was the partial reformation of LiF upon discharge which warrants further consideration for understanding CEI stability during cycling.	Jan 2018
I09-Surface and Interface Structural Analysis	Electrochemical and Thermal Stress of LiNi 0.8 Co 0.15 Al 0.05 O 2 Electrodes: Evolution of Aluminum Surface Environments Zachary W. Lebens-higgins , Nicholas Faenza , Pinaki Mukherjee , Shawn Sallis , Fadwa Badway , Nathalie Pereira , Christoph Schlueter , Tien-lin Lee , Frederic Cosandey , Glenn Amatucci , Louis F. J. Piper Ecs Transactions 80, 197 - 206 DOI: 10.1149/08010.0197ecst Show Abstract ▼ Abstract: For layered oxide cathodes, aluminum doping has widely been shown to improve performance, particularly at high degrees of delithiation. While this has led to increased interest in Al-doped systems, including LiNi0.8Co0.15Al0.05O2 (NCA), the aluminum surface environment has not been thoroughly investigated. Using hard x-ray photoelectron spectroscopy measurements of the Al 1s core region for NCA electrodes, we examined the evolution of the surface aluminum environment under electrochemical and thermal stress. By correlating the aluminum environment to transition metal reduction and electrolyte decomposition, we provide further insight into the cathode-electrolyte interface layer. A remarkable finding is that Al-O coatings in LiPF6 electrolyte mimic the evolution observed for the aluminum surface environment in doped layered oxides.	Dec 2017
I09-Surface and Interface Structural Analysis	Reaction heterogeneity in LiNi 0.8 Co 0.15 Al 0.05 O 2 induced by surface layer Antonin Grenier , Hao Liu , Kamila M. Wiaderek , Zachary W. Lebens-higgins , Olaf J. Borkiewicz , Louis F. J. Piper , Peter J. Chupas , Karena W. Chapman Chemistry Of Materials DOI: 10.1021/acs.chemmater.7b02236 Diamond Proposal Number(s): [12764, 16005] Show Abstract ▼ Abstract: Through operando synchrotron powder X-ray diffraction (XRD) analysis of layered transition metal oxide electrodes of composition LiNi0.8Co0.15Al0.05O2 (NCA), we decouple the intrinsic bulk reaction mechanism from surface-induced effects. For identically prepared and cycled electrodes stored in different environments, we demonstrate that the intrinsic bulk reaction for pristine NCA follows solid-solution mechanism, not a two-phase as suggested previously. By combining high resolution powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and surface sensitive X-ray photoelectron spectroscopy (XPS), we demonstrate that adventitious Li2CO3 forms on the electrode particle surface during exposure to air, through reaction with atmospheric CO2. This surface impedes ionic and electronic transport to the underlying electrode, with progressive erosion of this layer during cycling giving rise to different reaction states in particles with an intact vs an eroded Li2CO3 surface-coating. This reaction heterogeneity, with a bimodal distribution of reaction states, has previously been interpreted as a “two-phase” reaction mechanism for NCA, as an activation step that only occurs during the first cycle. Similar surface layers may impact the reaction mechanism observed in other electrode materials using bulk probes such as operando powder XRD.	Aug 2017
I09-Surface and Interface Structural Analysis	Electrolyte Induced Surface Transformation and Transition Metal Dissolution of Fully Delithiated LiNi 0.8 Co 0.15 Al 0.05 O 2 Nicholas V. Faenza , Zachary W. Lebens-higgins , Pinaki Mukherjee , Shawn Sallis , Nathalie Pereira , Fadwa Badway , Anna Halajko , Gerbrand Ceder , Frederic Cosandey , Louis F. J. Piper , Glenn G. Amatucci Langmuir DOI: 10.1021/acs.langmuir.7b00863 Diamond Proposal Number(s): [12764] Show Abstract ▼ Abstract: Enabling practical utilization of layered R-3m positive electrodes near full delithiation requires an enhanced understanding of the complex electrode-electrolyte interactions that often induce failure. Using Li[Ni0.8Co0.15Al0.05]O2 (NCA) as a model layered compound, the chemical and structural stability in a strenuous thermal and electrochemical environment was explored. Operando microcalorimetry and electrochemical impedance spectroscopy identified a fingerprint for a structural decomposition and transition metal dissolution reaction that occurs on the positive electrode at full delithiation. Surface sensitive characterization techniques, including X-ray absorption spectroscopy and high resolution transmission electron microscopy, measured a structural and morphological transformation of the surface and subsurface regions of NCA. Despite the bulk structural integrity being maintained, NCA surface degradation at a high state of charge induces excessive transition metal dissolution and significant positive electrode impedance development, resulting in a rapid decrease of electrochemical performance. Additionally, the impact of electrolyte salt, positive electrode surface area, and surface Li2CO3 content on the magnitude and character of the dissolution reaction was studied.	Jun 2017

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