Abstract

Ex situ transmission X-ray microscopy reveals micrometer-scale state-of-charge heterogeneity in solid-solution Li1- x Ni1/3 Co1/3 Mn1/3 O2 secondary particles even after extensive relaxation. The heterogeneity generates overcharged domains at the cutoff voltage, which may accelerate capacity fading and increase impedance with extended cycling. It is proposed that optimized secondary structures can minimize the state-of-charge heterogeneity by mitigating the buildup of nonuniform internal stresses associated with volume changes during charge.

Forecasting the health of a battery is a modeling effort that is critical to driving improvements in and adoption of electric vehicles. Purely physics-based models and purely data-driven models have advantages and limitations of their own. Considering the nature of battery data and end-user applications, we outline several architectures for integrating physics-based and machine learning models that can improve our ability to forecast battery lifetime. We discuss the ease of implementation, advantages, limitations, and viability of each architecture, given the state of the art in the battery and machine learning fields.

Ion insertion at the interfaces of batteries, fuel cells, and catalysts constitutes an important class of technologically relevant, charge-transfer reactions. However, the molecular nature of charge separation at the adsorbate/solid interface remains elusive. It has been hypothesized that electrostatic dipoles at the adsorbate/solid interface could result from adsorption-induced charge redistribution, preferential segregation of charged point defects in the solid, and/or intrinsic dipoles of adsorbates. Using operando ambient-pressure X-ray photoelectron spectroscopy, we elucidate the coupling between electrostatics and adsorbate chemistry on the surface of CeO2–x , an excellent electrocatalyst and a model system for studying oxygen-ion insertion reactions. Three adsorbate chemistries were studiedOH–/CeO2–x (polar adsorbate), CO3 2–/CeO2–x (nonpolar adsorbate), and Ar/CeO2–x (no adsorbate)under several hundred mTorr of gas pressure relevant to electrochemical H2/CO oxidation and H2O/CO2 reduction. By integrating core-level spectroscopy and contact-potential difference measurements, we simultaneously determine the chemistry and coverage of adsorbates, Ce oxidation state, and the surface potential at the gas/solid interface over a wide range of overpotentials. We directly observe an overpotential-dependent surface potential, which is moreover sensitive to the polarity of the adsorbates. In the case of CeO2–x covered with polar OH–, we observe a surface potential that increases linearly with OH– coverage and with overpotential. On the other hand, for CeO2–x covered with nonpolar CO3 2– and free of adsorbates, the surface potential is independent of overpotential. The adsorbate binding energy does not change systematically with overpotential. From these observations, we conclude that the electrostatic dipole at the adsorbate/CeO2–x interface is dominated by the intrinsic dipoles of the adsorbates, with the solid contributing minimally. These results provide an atomistic picture of the gas/solid double layer and the experimental methodology to directly study and quantify the surface dipole.

The efficacy of the electrical conductivity relaxation (ECR) technique for investigating the oxygen transport properties of mixed conducting oxides has been evaluated. Fifteen mol% samarium doped ceria (SDC15), for which approximate values of the two principal transport properties, bulk oxygen diffusivity, D Chem , and surface reaction rate constant, k S , can be found in the literature, was chosen as the benchmark material against which to validate the methodology. Measurements were carried out at temperatures between 750 • C and 850 • C and over a wide range of oxygen partial pressures. An unexpectedly high p-type electronic transference number enabled ECR measurements under oxidizing conditions. A systematic data analysis procedure was developed to permit reliable extraction of the kinetic parameters even in the general case of simultaneous bulk and surface limitation. The D Chem from this study showed excellent qualitative and quantitative agreement with expected values, falling in the range from ∼ 2 × 10 −5 to 2 × 10 −4 cm 2 /s. The surface reaction constant under H 2 /H 2 O mixtures also showed good agreement with literature results. Remarkably, this value increased by a factor of 40 under mixtures of CO/CO 2 or O 2 /Ar. This observation suggests kinetic advantages for production of CO rather than H 2 in a two-step solar-driven thermochemical process based on samarium doped ceria.