Concentration Gradient Induced Delithiation Failure of MoO3 for Li-Ion Batteries

Binder-Free MoO2-MoO3 Nanoarrays as High-Performance Anodes for Li-Ion Batteries

To overcome the limitations of commercializing lithium-ion batteries (LIBs), a one-step feasible route is reported to prepare a hybrid matrix of molybdenum oxides (MoO3-x, x = 0 and 1) thin film anode. In this direction, the electrical conductivity barriers of MoO3 dielectric are overcome by reinforcing conductive MoO2 via the chemical vapor deposition (CVD) route. The intermixed array of nanograins and nanoflakes grown over stainless-steel (SS) foil delivers a maximum gravimetric capacitance of 281 F g-1 and a specific capacity of 348 mAh g-1 at 1 A g-1. The synergistic integration of metal oxides facilitates multiple valencies, interfacial structural stability, and abundant ion transport channels to achieve a wider voltage window of 3.50 V. Subsequently, the prepared Li||MoO2-MoO3@SS configuration possesses electric double-layer and pseudocapacitive energy storage capacity leading to remarkable specific energy 77.78 Wh kg-1 and excellent specific power 13.75 kW kg-1. The high-rate capacity tests for continuous 1200 charge-discharge cycles disclose retention of ≈88% and ≈100% Coulombic efficiency on a 2-fold enlargement of current density. The longer lifespan and higher rate capacity of nanohybrid anode owing to reversible lithiation/delithiation further recommend its candidacy in developing LIBs for next-generation portable electronics.

Deciphering Structural Origins of Highly Reversible Lithium Storage in High Entropy Oxides with In Situ Transmission Electron Microscopy

Configurational entropy-stabilized single-phase high-entropy oxides (HEOs) have been considered revolutionary electrode materials with both reversible lithium storage and high specific capacity that are difficult to fulfill simultaneously by conventional electrodes. However, precise understanding of lithium storage mechanisms in such HEOs remains controversial due to complex multi-cationic oxide systems. Here, distinct reaction dynamics and structural evolutions in rocksalt-type HEOs upon cycling are carefully studied by in situ transmission electron microscopy (TEM) including imaging, electron diffraction, and electron energy loss spectroscopy at atomic scale. The mechanisms of composition-dependent conversion/alloying reaction kinetics along with spatiotemporal variations of valence states upon lithiation are revealed, characterized by disappearance of the original rocksalt phase. Unexpectedly, it is found from the first visualization evidence that the post-lithiation polyphase state can be recovered to the original rocksalt-structured HEOs via reversible and symmetrical delithiation reactions, which is unavailable for monometallic oxide systems. Rigorous electrochemical tests coupled with postmortem ex situ TEM and bulk-level phase analyses further validate the crucial role of structural recovery capability in ensuring the reversible high-capacity Li-storage in HEOs. These findings can provide valuable guidelines to design compositionally engineer HEOs for almighty electrodes of next-generation long-life energy storage devices.

Retarding the Shuttling Ions in the Electrochromic TiO2 with Extensive Crystallographic Imperfections

To understand the role of structure imperfections on the performance of electrochromic transition metal oxide (ETMO) is challenging for the design of efficient smart windows. Herein, we investigate the performance evolution with tunable crystallographic imperfections for rutile TiO₂ nanowire film (TNF). Structure imperfections, originating mainly from the copious oxygen deficiency, are apt to cumulatively retard the shuttling ions, resulting in the response rate for raw TNF being less than the half that of TNF annealed at 500 °C. We describe ion accommodation sites as a convolution of normal site and abnormal site, in which the normal site performs reversible coloration but the abnormal site contributes only to charge storage, which gives a rationale for the non-linear coloration and rate capability loss. These findings give a clear picture of the ion shuttling process, which is insightful for enhancing the electrochromic performance via structure reprogramming.

Mesoporous WS2/MoO3 Hybrids for High-Performance Trace Ammonia Detection

Mesoporous WS₂/MoO₃ hybrids were synthesized by a facile two-step and additive-free hydrothermal approach and employed for high-performance trace ammonia gas (NH₃) detection. Compared with single WS₂ and MoO₃ counterparts, WS₂/MoO₃ sensors exhibited an improvement in NH₃-sensing performance at room temperature (22 ± 3 °C). Typically, the optimal WS₂/MoO₃ sensor showed a higher and quicker response of 31.58% within 57 s toward 3 ppm of NH₃, which was 17.7- and 57.4-fold larger than that of pure MoO₃ (1.78% within 251 s) and WS₂ (0.55% within 153 s) ones. Meanwhile, good reversibility, sensitivity, and selectivity, reliable long-term stability, and the lowest detection limit of 9.0 ppb were achieved. These superior properties were probably ascribed to numerous heterojunctions favorable for additional carrier-concentration modulation via the synergetic effect between WS₂ and MoO₃ components and the large specific surface area beneficial for richer sorption sites and faster molecular transfer at room temperature. Such achievements also imply that the designed WS₂/MoO₃ heterostructure nanomaterials have the potential in achieving trace NH₃ recognition catering for the requirements of high sensitivity and low power consumption in future gas sensors.