This review addresses concepts, approaches, tools, and outcomes of multiscale modeling used to design and optimize the current and next generation rechargeable battery cells. Different kinds of multiscale models are discussed and demystified with a particular emphasis on methodological aspects. The outcome is compared both to results of other modeling strategies as well as to the vast pool of experimental data available. Finally, the main challenges remaining and future developments are discussed.

Sodium-ion batteries (SIBs) are currently being considered for large-scale energy storage. Optimisation of SIB electrolytes is, however, still largely lacking. Here we exhaustively evaluate NaPF 6 in diglyme as an electrolyte of choice-both physico-chemical properties and extensive electrochemical tests including half as well as full cells. Fundamentally, the ionic conductivity is found to be quite comparable to carbonate based electrolytes and obeying the fractional Walden rule with viscosity. We find Na metal to work well as a reference electrode and the electrochemical stability, evaluated potentiostatically for various electrodes and corroborated by DFT calculations, to be satisfactory in the entire voltage range of 0-4.4 V. Galvanostatic cycling at C/10 of half and full cells using Na 3 V 2 (PO 4) 3 (NVP) or Na 3 V 2 (PO 4) 2 F 3 (NVPF) as cathodes and hard carbon (HC) as anodes indicate rapid capacity fading in cells with HC anodes, possibly originating in a lack of a stable SEI or by trapping of sodium. Aiming to understand this capacity fade further, we conducted a GC/MS analysis to determine electrolyte reduction products and to propose reduction pathways, concluding that oligomer and/or alkoxide formation is possible. Overall, the promising results should warrant further investigations of diglyme based electrolytes for modern SIB development, albeit avoiding HC anodes.