Potential Energy Calculations for Water Adsorption on Poly (methyl methacrylate)

Mateusz J. Zuba, P. Howard, B. Familo, T. Kane, R. Netusil, and C. C. Ilie The generosity of the NOYCE Research Grant enabled me to focus on the study of various polymers. The main goal was to study the molecular orbitals of poly (methyl methacrylate) (PMMA) and calculate the energy band gap. We obtained the activation energy from thermal desorption spectra of water on poly (methyl methacrylate) by employing Arrhenius analysis. Thermal desorption of PMMA is coverage independent with peaks at the same temperature. Activation energy of desorption may increase with increasing water coverage, i.e. the amount of water exposed to the system. We also performed the potential energy calculations for our system: two polymer chains and water molecules. The method by which potential energy calculations were performed involved HyperChem Professional 8.0; a very sophisticated molecular modeling software known for its quality, flexibility, and ease of use. As seen using HyperChem water molecules take a favorable position above the PMMA chains. Double bonded oxygen atoms of PMMA favor the Hydrogen atoms of the water molecule. CH3 ligands tend to turn the oxygen of water down towards the polymer backbone. Potential energy plots (in eV) for the water molecule as a function of distance from PMMA chains along the lateral to the backbone chain were obtained. These calculations were used in scientific papers

How Bulk Sensitive is Hard X-ray Photoelectron Spectroscopy: Accounting for the Cathode-Electrolyte Interface when Addressing Oxygen Redox.

Sensitivity to the "bulk" oxygen core orbital makes hard X-ray photoelectron spectroscopy (HAXPES) an appealing technique for studying oxygen redox candidates. Various studies have reported an additional O 1s peak (530-531 eV) at high voltages, which has been considered a direct signature of the bulk oxygen redox process. Here, we find the emergence of a 530.4 eV O 1s HAXPES peak for three model cathodes-Li2MnO3, Li-rich NMC, and NMC 442-that shows no clear link to oxygen redox. Instead, the 530.4 eV peak for these three systems is attributed to transition metal reduction and electrolyte decomposition in the near-surface region. Claims of oxygen redox relying on photoelectron spectroscopy must explicitly account for the surface sensitivity of this technique and the extent of the cathode degradation layer

Understanding improved capacity retention at 4.3 V in modified single crystal Ni-rich NMC//graphite pouch cells at elevated temperature

The capacity retention of commercially-sourced pouch cells with single crystal Al surface-doped Ni-rich cathodes (LiNi0.834Mn0.095Co0.071O2) is examined. The degradation-induced capacity fade becomes more pronounced as the upper-cut-off voltage (UCV) increases from 4.2 V to 4.3 V (vs. graphite) at a fixed cycling temperature (either 25 or 40 °C). However, cycles with 4.3 V UCV (slightly below the oxygen loss onset) show better capacity retention upon increasing the cycling temperature from 25 °C to 40 °C. Namely, after 500 cycles at 4.3 V UCV, cycling temperature at 40 °C retains 85.5% of the initial capacity while cycling at 25 °C shows 75.0% capacity retention. By employing a suite of electrochemical, X-ray spectroscopy and secondary ion mass spectrometry techniques, we attribute the temperature-induced improvement of the capacity retention at high UCV to the combined effects of Al surface-dopants, electrochemically resilient single crystal Ni-rich particles, and thermally-improved Li kinetics translating into better electrochemical performance. If cycling remains below the lattice oxygen loss onset, improved capacity retention in industrial cells should be achieved in single crystal Ni-rich cathodes with the appropriate choice of cycling parameter, particle quality, and particle surface dopants

Understanding improved capacity retention at 4.3 V in modified single crystal Ni-rich NMC//graphite pouch cells at elevated temperature

The capacity retention of commercially-sourced pouch cells with single crystal Al surface-doped Ni-rich cathodes (LiNi0.834Mn0.095Co0.071O2) is examined. The degradation-induced capacity fade becomes more pronounced as the upper-cut-off voltage (UCV) increases from 4.2 V to 4.3 V (vs. graphite) at a fixed cycling temperature (either 25 or 40 °C). However, cycles with 4.3 V UCV (slightly below the oxygen loss onset) show better capacity retention upon increasing the cycling temperature from 25 °C to 40 °C. Namely, after 500 cycles at 4.3 V UCV, cycling temperature at 40 °C retains 85.5% of the initial capacity while cycling at 25 °C shows 75.0% capacity retention. By employing a suite of electrochemical, X-ray spectroscopy and secondary ion mass spectrometry techniques, we attribute the temperature-induced improvement of the capacity retention at high UCV to the combined effects of Al surface-dopants, electrochemically resilient single crystal Ni-rich particles, and thermally-improved Li kinetics translating into better electrochemical performance. If cycling remains below the lattice oxygen loss onset, improved capacity retention in industrial cells should be achieved in single crystal Ni-rich cathodes with the appropriate choice of cycling parameter, particle quality, and particle surface dopants

Evidence of a second-order Peierls-driven metal-insulator transition in crystalline NbO2

The metal-insulator transition of NbO2 is thought to be important for the functioning of recent niobium oxide-based memristor devices, and is often described as a Mott transition in these contexts. However, the actual transition mechanism remains unclear, as current devices actually employ electroformed NbOx that may be inherently different to crystalline NbO2. We report on our synchrotron x-ray spectroscopy and density-functional-theory study of crystalline, epitaxial NbO2 thin films grown by pulsed laser deposition and molecular beam epitaxy across the metal-insulator transition at ~810⁰C. The observed spectral changes reveal a second-order Peierls transition driven by a weakening of Nb dimerization without significant electron correlations, further supported by our density-functional-theory modeling. Our findings indicate that employing crystalline NbO2 as an active layer in memristor devices may facilitate analog control of the resistivity, whereby Joule-heating can modulate Nb-Nb dimer distance and consequently control the opening of a pseudogap

31st Annual Meeting and Associated Programs of the Society for Immunotherapy of Cancer (SITC 2016) : part two

Background The immunological escape of tumors represents one of the main ob- stacles to the treatment of malignancies. The blockade of PD-1 or CTLA-4 receptors represented a milestone in the history of immunotherapy. However, immune checkpoint inhibitors seem to be effective in specific cohorts of patients. It has been proposed that their efficacy relies on the presence of an immunological response. Thus, we hypothesized that disruption of the PD-L1/PD-1 axis would synergize with our oncolytic vaccine platform PeptiCRAd. Methods We used murine B16OVA in vivo tumor models and flow cytometry analysis to investigate the immunological background. Results First, we found that high-burden B16OVA tumors were refractory to combination immunotherapy. However, with a more aggressive schedule, tumors with a lower burden were more susceptible to the combination of PeptiCRAd and PD-L1 blockade. The therapy signifi- cantly increased the median survival of mice (Fig. 7). Interestingly, the reduced growth of contralaterally injected B16F10 cells sug- gested the presence of a long lasting immunological memory also against non-targeted antigens. Concerning the functional state of tumor infiltrating lymphocytes (TILs), we found that all the immune therapies would enhance the percentage of activated (PD-1pos TIM- 3neg) T lymphocytes and reduce the amount of exhausted (PD-1pos TIM-3pos) cells compared to placebo. As expected, we found that PeptiCRAd monotherapy could increase the number of antigen spe- cific CD8+ T cells compared to other treatments. However, only the combination with PD-L1 blockade could significantly increase the ra- tio between activated and exhausted pentamer positive cells (p= 0.0058), suggesting that by disrupting the PD-1/PD-L1 axis we could decrease the amount of dysfunctional antigen specific T cells. We ob- served that the anatomical location deeply influenced the state of CD4+ and CD8+ T lymphocytes. In fact, TIM-3 expression was in- creased by 2 fold on TILs compared to splenic and lymphoid T cells. In the CD8+ compartment, the expression of PD-1 on the surface seemed to be restricted to the tumor micro-environment, while CD4 + T cells had a high expression of PD-1 also in lymphoid organs. Interestingly, we found that the levels of PD-1 were significantly higher on CD8+ T cells than on CD4+ T cells into the tumor micro- environment (p < 0.0001). Conclusions In conclusion, we demonstrated that the efficacy of immune check- point inhibitors might be strongly enhanced by their combination with cancer vaccines. PeptiCRAd was able to increase the number of antigen-specific T cells and PD-L1 blockade prevented their exhaus- tion, resulting in long-lasting immunological memory and increased median survival

Surface reduction stabilizes the single-crystalline Ni-Rich layered cathode for Li-Ion batteries

The surface of the layered transition metal oxide cathode plays an important role in its function and degradation. Modification of the surface structure and chemistry is often necessary to overcome the debilitating effect of the native surface. Here, we employ a chemical reduction method using CaI2 to modify the native surface of single-crystalline layered transition metal oxide cathode particles. High-resolution transmission electron microscopy shows the formation of a conformal cubic phase at the particle surface, where the outmost layer is enriched with Ca. The modified surface significantly improves the long-term capacity retention at low rates of cycling, yet the rate capability is compromised by the impeded interfacial kinetics at high voltages. The lack of oxygen vacancy generation in the chemically induced surface phase transformation likely results in a dense surface layer that accounts for the improved electrochemical stability and impeded Li-ion diffusion. This work highlights the strong dependence of the electrode’s (electro)chemical stability and intercalation kinetics on the surface structure and chemistry, which can be further tailored by the chemical reduction method

Irreversible anion oxidation leads to dynamic charge compensation in the Ru-poor, Li-rich cathode Li2Ru0.3Mn0.7O3

Conventional cathodes for Li-ion batteries are layered transition-metal oxides that support Li+ intercalation charge-balanced by redox on the transition metals. Oxidation beyond one electron per transition metal can be achieved in Li-rich layered oxides by involving structural anions, which necessitates high voltages and complex charge compensation mechanisms convoluted by degradation reactions. We report a detailed structural and spectroscopic analysis of the multielectron material Li2Ru0.3Mn0.7O3, chosen due to its low Ru content. Ex situ and operando spectroscopic data over multiple cycles highlight the changing charge compensation mechanism. Notably, over half of the first-cycle capacity is attributed to O2 gas evolution and reversible O redox is minimal. Instead, reduced Ru and Mn species are detected in the bulk and on the surface, which then increasingly contribute to charge compensation as more metal reduction occurs with cycling. Permanent structural changes linked to metal migration are observed with EXAFS and Raman analysis

Regeneration of degraded Li-rich layered oxide materials through heat treatment-induced transition metal reordering

Lithium-rich layered oxides (LRLO) have drawn great attention recently as a high energy density cathode material. However, the practical deployment of this materials is hindered by voltage and capacity decay during electrochemical cycling. Applying mild thermal energy to cycled LRLO materials allows to recover the decayed voltage. In this work, a detailed mechanism study of the voltage and structure recovery is conducted through various analytical tools. Heat treatment provides the necessary energy for the transition metal to overcome the kinetic barrier to move from honeycomb center to honeycomb vertex and recover the honeycomb ordering in the transition metal layer. An ambient-air relithiation using Li+ molten salt was also conducted along with the heat treatment to the cycled LRLO cathode and lead to a material regeneration in both the voltage and capacity. This work identifies the transition metal reordering as the key factor under the structure recovery of degraded LRLO materials. It opens a door for the promising strategies to mitigate the voltage and capacity degradation problem in LRLO and provides the potential routes to recycle degraded LRLO materials