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The performance, safety, and reliability of Li-ion batteries are determined by a complex set of multiphysics, multiscale phenomena that must be holistically studied and optimized. This paper provides a summary of the state of the art in a variety of research fields related to Li-ion battery materials, processes, and systems. The material presented here is based on a series of discussions at a recently concluded bilateral workshop in which researchers and students from India and the U.S. participated. It is expected that this summary will help understand the complex nature of Li-ion batteries and help highlight the critical directions for future research.

Complementary X-ray absorption fine structure (XAFS) and Raman spectroscopy studies were conducted on various UCl 3 concentrations in alkali chloride salt compositions. The samples were 5 mol % UCl 3 in LiCl (S1), 5 mol % UCl 3 in KCl (S2), 5 mol % UCl 3 in LiCl-KCl eutectic (S4), 50 mol % UCl 3 in KCl (S5), and 20 mol % UCl 3 in KCl (S6) molar concentrations. Samples were heated to 800 °C and allowed to cool to room temperature with measurements performed at selected temperatures; the highest temperatures showed the most stability and will be primarily referenced for conclusions. The processing and interpretation of the Raman and extended X-ray absorption fine structure (EXAFS) peaks revealed several uranium-oxygen bond lengths and symmetries in the samples before, during, and after heating. Based on published thermodynamic data of similar systems, X-ray absorption fine structure spectroscopy, and identification of Raman peaks, a β variation of α-U 3 O 8 , typical at room temperature, is the suspected dominant phase of all samples at high temperatures (800 °C). In the existing literature, this β structure of U 3 O 8 was synthesized by slow cooling of uranium oxides from 1350 °C. This paper suggests the rapid formation of the compound due to the decomposition of the uranium chlorides or oxychlorides at increasing temperatures and O 2 reaction kinetics.

Complementary X-ray absorption fine structure (XAFS) spectroscopy and Raman spectroscopy studies were conducted on several UCl 3 concentrations in several chloride salt compositions. The samples were 5% UCl 3 in LiCl (S1), 5% UCl 3 in KCl (S2), 5% UCl 3 in LiCl-KCl eutectic (S3), 5% UCl 3 in LiCl-KCl eutectic (S4), 50% UCl 3 in KCl (S5), and 20% UCl 3 in KCl (S6) molar concentrations. Sample S3 had UCl 3 sourced from Idaho National Laboratory (INL), and all other samples were UCl 3 sourced from TerraPower. The initial compositions were prepared in an inert and oxygen-free atmosphere. XAFS measurements were performed in the atmosphere at a beamline, and Raman spectroscopy was conducted inside a glovebox. Raman spectra were able to confirm initial UCl 3 . XAFS and later Raman spectra measured, however, did not correctly match the literature and computational spectra for the prepared UCl 3 salt. Rather, the data shows some complex uranium oxychloride phases at room temperature that transition into uranium oxides upon heating. Oxygen pollution due to failure of the sealing mechanism can result in oxidation of the UCl 3 salts. The oxychlorides present may be both a function of the unknown O 2 exposure concentration, depending on the source of the leak and the salt composition. Evidence of this oxychloride claim and its subsequent decomposition is justified in this work.

Understanding the local environment of the metal atoms in salt melts is important for modeling the properties of melts and predicting their behavior and thus helping enable the development of technologies such as molten salt reactors and solar-thermal power systems and new approaches to recycling rare-earth metals. Toward that end, we have developed an in situ approach for measuring the coordination of metals in molten salt coupling X-ray absorption spectroscopy (XAS) and Raman spectroscopy. Our approach was demonstrated for two salt mixtures (1.9 and 5 mol % SrCl 2 in NaCl, 0.8 and 5 mol % ZrF 4 in LiF) at up to 1100 °C. Near-edge (X-ray absorption near-edge structure, XANES) and extended X-ray absorption fine structure (EXAFS) spectra were measured. The EXAFS response was modeled using ab initio FEFF calculations. Strontium's first shell is observed to be coordinated with chlorine (Sr 2+ -Cl - ) and zirconium's first shell is coordinated by fluorine (Zr 4+ -F - ), both having coordination numbers that decrease with increasing temperature. Multiple zirconium complexes are believed to be present in the melt, which may interfere and distort the EXAFS spectra and result in an anomalously low zirconium first shell coordination number. The use of boron nitride (BN) powder as a salt diluent for XAFS measurements was found to not interfere with measurements and thus can be used for investigations of such systems.

Graded foam-filled channels are a very promising solution for improving the thermal performance of heat sinks because of their customized structures that leave large amounts of room for heat transfer enhancement. Accordingly, this paper proposes a comprehensive optimization framework to address the design of such components, which are subjected to a uniform heat flux boundary condition. The graded foam is achieved by parameterizing the spatial distributions of porosity and/or Pores Per Inch (PPI). Mono- and multi-objective optimizations are implemented to find the best combination of the foam's fluid-dynamic, geometrical and morphological design variables. The mono-objective approach addresses the Performance Evaluation Criterion (PEC) as an objective function to maximize the thermal efficiency of graded foams. The multi-objective approach addresses different objective functions by means of Pareto optimization to identify the optimal tradeoff solutions between heat transfer enhancement and pressure drop reduction. Optimizations are performed by assuming a local thermal non-equilibrium in the foam. They allowed us to achieve a 1.51 PEC value with H* = 0.50, Re H = 15000, i ε = i PPI = 0.50, ε (0) = 0.85, ε (1) = 0.97, PPI(0) = 5, PPI(1) = 40, and k s →f = 10 4 as the design variables. For the three multi-objective functions investigated, one can extrapolate the optimum from the Pareto front via the utopia criterion, obtaining h¯ = 502 W/m 2 K and Δ p = 80 Pa, NuH,unif¯ = 2790 and f = 42, ⟨Ts*⟩s¯= 0.011, and Δ p* = 91. The optimal solutions provide original insights and guidelines for the thermal design of graded foam-filled channels.