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.

Molybdenum(IV) sulfide (MoS 2 ) has generated significant interest as an electroactive material for Li-ion batteries because of its high theoretical capacity, good rate capability, and minimal volume changes during cycling. An important challenge toward implementing this material is understanding the many polymorphs of MoS 2 that can be (de)stabilized by electrochemical lithiation and nanosizing. To this end, bulk MoS 2 and nanosheet-type MoS 2 were characterized both as solids (X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasmaoptical emission spectroscopy (ICP-OES)) and during electrochemical cycling within operando X-ray analysis compatible lithium cells (operando XRD and ex situ XAS). In situ XRD shows that the bulk 2H-MoS 2 phase is converted to 1T-Li x MoS 2 upon discharge and that this change is only partially reversible upon charge. Furthermore, operando XRD identifies the nanosheet MoS 2 as the metastable 1T′ phase and shows that this phase is conserved upon discharge. Ex situ XAS provides additional structural insights into the local structure of MoS 2 , confirming that the 1T′ phase is the correct assignment of the nanosheet MoS 2 and revealing an irreversible local distortion that occurs during cycling. This local distortion is likely a factor in the increased capacity fade observed in the nanosheet cells. This work provides important insights into the structure of MoS 2 and how that structure is affected by nanosizing and cycling, which can inform other studies of nanosheet layered materials.

Ni-rich NMC is an attractive Li-ion battery cathode due to its combination of energy density, thermal stability, and reversibility. While higher delivered energy density can be achieved with a more positive charge voltage limit, this approach compromises sustained reversibility. Improved understanding of the local and bulk structural transformations as a function of charge voltage, and their associated impacts on capacity fade are critically needed. Through simultaneous operando synchrotron X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) of cells cycled at 3–4.3 or 3–4.7 V, this study presents an in-depth investigation into the effects of voltage window on local coordination, bulk structure, and oxidation state. These measurements are complemented by ex situ X-ray fluorescence (XRF) mapping and scanning electrochemical microscopy mapping (SECM) of the negative electrode, X-ray photoelectron spectroscopy (XPS) of the positive electrode, and cell level electrochemical impedance spectroscopy (EIS). Initially, cycling between 3 and 4.7 V leads to greater delivered capacity due to greater lithium extraction, accompanied by increased structural distortion, moderately higher Ni oxidation, and substantially higher Co oxidation. Continued cycling at this high voltage results in suppressed Ni and Co redox, greater structural distortion, increased levels of transition metal dissolution, higher cell impedance, and 3× greater capacity fade.

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...