Layered MoO3 represents a promising cathode for aqueous rechargeable Zn‐ion batteries, but the implementation of this material is limited due to the low conductivity and poor structural stability. A 30 m ZnCl2 water‐in‐salt electrolyte (WISE) is introduced to a MoO3 nanobelt cathode for the first time, significantly increasing the stability of MoO3 cathodes compared to those in 3 m ZnSO4 and 3 m ZnCl2. The Zn/MoO3 cell in WISE unambiguously demonstrate significantly improved rate performance delivering 349, 253, and 222 mAh g−1 at 100, 500, and 1000 mA g−1, denoting a 12× capacity increase of those achieved in 3 m electrolytes at 1000 mA g−1. A capacity retention rate of 73% is achieved after (dis)charging at 100 mA g−1 for 100 cycles, and no obvious capacity fading is observed at higher current densities of 500 mA g−1 and 2 A g−1. Specifically, the data suggest that the drastic fading in 3 m electrolytes can be attributed to the parasitic surface deposits on Zn originated from Mo dissolution and H2 formation due to Zn corrosion and hydrogen evolution reaction, which are significantly suppressed in the WISE. The direct visualization of these side reactions is achieved for the first time in the Zn‐MoO3 system, using an in situ optoelectrochemical measurement.

The phase distribution of lithiated LVO in thick (~500 µm) porous electrodes (TPE) designed to facilitate both ion and electron transport was determined using synchrotron-based operando energy dispersive x-ray diffraction...

Measuring tortuosity in porous electrodes is important for understanding rate capability and optimizing design. Here, we describe an approach to determine electrode tortuosities and quantify the associated uncertainties by fitting a P2D model to discharge profiles from a standard rate capability test. A dimensionless current is identified as a design-of-experiment parameter that can be used to identify experiments that return confident estimates of tortuosity, even when other model parameters are not known with certainty. This approach is applied to analysis of L i x V 3 O 8 (LVO) electrodes and L i x N i 0.33 M n 0.33 C o 0.33 O 2 (NMC) electrodes. The details of the assumptions made in these measurements and their impact on the reported uncertainties are discussed. We also perform an uncertainty analysis on the standard method for quantifying tortuosity in the literature: electrochemical impedance spectroscopy collected under blocking electrolyte conditions. We find that confident estimates can be obtained using this approach even when uncertainties in equivalent circuit model parameters are considered.

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