Electrolyte systems based on binary mixtures of organic carbonate ester cosolvents have limitations in ionic transport and thus limit extreme fast charge (XFC) and high-rate cycling of energy dense lithium-ion cells with thick electrodes (>80 μm per side) at ambient temperature and below. Here, we present LiPF6 in methyl acetate (MA) as an ester-based liquid electrolyte that offers substantial improvements in ionic transport, doubling the conductivity of conventional electrolyte systems. Density functional theory-based molecular dynamics (DFT-MD) simulations give insights into the experimentally observed low solvation number for lithium ions in MA solutions and show a solution system with highly mobile, loosely bound ionic species. We show that MA-based electrolytes with suitable additive formulas enable high cycling rates and excellent low-temperature cycling performance in lithium-ion cell designs with thick electrodes but come with a trade-off in lifetime at elevated temperature. While there are inherent practical issues with MA as an electrolyte solvent, including a low flash point (−10 °C) and lifetime penalties compared to state-of-the-art electrolytes, this work demonstrates that excellent ionic transport in the electrolyte can enable fast charging without the energy density sacrifice inherently associated with specifically tailored electrodes. Further work in electrolyte design, particularly in increasing ionic conductivity without sacrificing stability, has the potential to enable XFC in practical lithium-ion cell chemistries and cell designs.

A few weight percent of electrolyte additives can dramatically improve Li-ion battery performance and lifetime. A systematic investigation of a series of electrolyte additive formulations was performed on bimodal (BM) and single crystal (SC) LiNi0.8Mn0.1Co0.1O2 (NMC811)/artificial graphite (AG) pouch cells. Long-term cycling tests at different temperatures (20 °C, 40 °C, and 55 °C) and different upper cutoff voltages (4.06 V and 4.20 V) were performed. These tests results were combined with advanced characterization techniques like ultra-high precision charging (UHPC), ex-situ gas measurement, and automatic cell storage tests to rank the additives based on their effectiveness. Radar plots and a figure-of-merit (FOM) approach were further utilized to summarize results for the BM and SC NMC811/AG cells. This work provides a useful benchmark for those developing NMC811/graphite cells and gives important insights for future electrolyte additive studies.

Semiconducting ferroelectric materials with low energy polarization switching offer a platform for next‐generation electronics such as ferroelectric field‐effect transistors. Recently discovered interfacial ferroelectricity in bilayers of transition metal dichalcogenide films provides an opportunity to combine the potential of semiconducting ferroelectrics with the design flexibility of 2D material devices. Here, local control of ferroelectric domains in a marginally twisted WS2 bilayer is demonstrated with a scanning tunneling microscope at room temperature, and their observed reversible evolution is understood using a string‐like model of the domain wall network (DWN). Two characteristic regimes of DWN evolution are identified: (i) elastic bending of partial screw dislocations separating smaller domains with twin stackings due to mutual sliding of monolayers at domain boundaries and (ii) merging of primary domain walls into perfect screw dislocations, which become the seeds for the recovery of the initial domain structure upon reversing electric field. These results open the possibility to achieve full control over atomically thin semiconducting ferroelectric domains using local electric fields, which is a critical step towards their technological use.

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