No abstract

No abstract

Interatomic potential simulation techniques have been applied to both the bulk and surfaces of yttrium-stabilized cubic zirconia (YSZ). In the Mott−Littleton bulk calculations representing the infinitely dilute system, the yttrium dopants tend to exist as a pair with two yttriums close to each other and preferentially occupying the next-nearest neighbor (NNN) sites to the oxygen vacancy. However, the energy of the YSZ system as well as the configuration of defect cluster depends on the dopant concentration level. The calculated lattice energy for supercell models linearly increases with yttria content. At around 10% mol Y2O3, the simulations indicate the existence of two stable cubiclike phases differencing in term of the detached arrangement of oxygen ions. Surface-energy calculations confirm the dominance of the (111) surface in c-ZrO2 and YSZ. The yttrium solution energy at the surface has been estimated as a function of the Y dopant-vacancy cluster depth. The calculations demonstrate that for yttrium segregation to the top layers of the (111) surface. However, there is no evidence for strong segregation to the (110) surface.

The reactivity of sodium inserted hard carbon with ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), EC:DEC, EC:DMC and NaPF 6 EC:DEC (/DMC) electrolytes was studied by Accelerating Rate Calorimetry (ARC), and the products after the ARC experiments were investigated by X-ray diffraction. The results show that sodium inserted hard carbon reacts with DMC to form sodium methyl carbonate, and that it reacts with EC and DEC to form sodium alkyl carbonates which apparently have a similar structure to sodium methyl carbonate. Sodium inserted hard carbon is more reactive with DMC and DEC than with EC. Finally, Na inserted hard carbon is more reactive in NaPF 6 EC:DEC and NaPF 6 EC:DMC than in EC:DEC and EC:DMC due to the high thermal stability of NaPF 6 and preferential solvation of NaPF 6 by EC, which leaves DEC and DMC available for reaction. The reactivity of Li inserted hard carbon was also compared to the reactivity of Na inserted hard carbon in both solvent and electrolyte and it was found that Li inserted hard carbon shows much better thermal stability.

Li-ion pouch cells were made to study the factors that influence gas evolution during formation (first charge). Electrode materials, electrolyte additives and temperature were varied. Measurements were made using the Archimedes' In Situ Gas Analyzer at Dalhousie University. When cells are charged to high voltages (>4.2 V) there is gas evolution, presumed to be from reactions on the surface of the positive electrode. This is separate from the gas evolution known to happen at lower voltage (<3.5 V) caused by reactions on the negative electrode. Both evolutions were characterized by the magnitude of volume changes and their onset voltages. Gas volumes appear to increase and onset voltages decrease, respectively, with increasing temperature. Use of the additive prop-1-ene-1,3-sultone at 2% by weight in Li[Ni 0.42 Mn 0.42 Co 0.16 ]O 2 /graphite cells yields smaller volume and higher onset voltage of gas evolution at all temperatures, compared to other additives tested. Certain cathode materials, namely some coated LiCoO 2 samples, can be charged to high voltages (≤4.7 V) without producing gas at high voltage.

No abstract

The unfavorable morphology and inefficient utilization of phase transition reversibility have limited the high‐temperature‐processed inorganic perovskite films in both efficiency and stability. Here, a simple soft template‐controlled growth (STCG) method is reported by introducing (adamantan‐1‐yl)methanammonium to control the nucleation and growth rate of CsPbI3 crystals, which gives rise to pinhole‐free CsPbI3 film with a grain size on a micrometer scale. The STCG‐based CsPbI3 perovskite solar cell exhibits a power conversion efficiency of 16.04% with significantly reduced defect densities and charge recombination. More importantly, an all‐inorganic solar cell with the architecture fluorine‐doped tin oxide (FTO)/NiOx/STCG‐CsPbI3/ZnO/indium‐doped tin oxide (ITO) is successfully fabricated to demonstrate its real advantage in thermal stability. By suppressing the inductive effect of defects during the phase transition and utilizing the unique reversibility of the phase transition for the high‐temperature‐processed CsPbI3 film, the all‐inorganic solar cell retains 90% of its initial efficiency after 3000 h of continuous light soaking and heating.

It has long been suspected that parasitic reaction products created at one electrode of a Li-ion battery can migrate to the other electrode and influence its operation. In order to demonstrate that these “electrode-electrode interactions” do occur, four types of coin cells were investigated. Two of these were Li4Ti5O12-limited and LiNi0.5Mn1.5O4-limited LiNi0.5Mn1.5O4/Li4Ti5O12 (LNMO/LTO) “full cells”. In order to prevent electrode-electrode interactions, LTO/Li and Li/LNMO coin cells were connected by a wire joining the negative (Li) sides of the two coin cells making a simulated LNMO/LTO Li-ion cell with separate electrolyte compartments for the positive and negative electrodes. Virtually no parasitic reactions were observed at the LTO electrode in Li/LTO cells as evidenced by a coulombic efficiency near 1.0000. By contrast, severe electrolyte oxidation, leading to charge end point capacity slippage and poor coulombic efficiency was observed in Li/LNMO cells. The behavior of the simulated LNMO/LTO Li-ion cells could be well understood and predicted based on the behavior of the half cells. By contrast, true LNMO/LTO Li-ion cells showed severe parasitic reactions occurring at the LTO electrode due to electrolyte oxidation products from the LNMO electrode migrating to the LTO electrode. Understanding such electrode-electrode interactions is critical in making long-lived Li-ion batteries and also for understanding the mechanisms governing the function of electrolyte additives. Similar effects, albeit at much smaller effective currents, can be occurring in Li-ion cells with standard positive and negative electrodes.