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  1. Two-dimensional (2D) tungsten disulfide nanosheets (WS2) could be a promising candidate for high-performance self-powered photodetectors. The present 2D nanosheets were obtained from liquid exfoliation in a mixture of ethanol, methanol, and isopropanol via a direct dispersion and ultrasonication method. Using the spin-coating technique, a thin film of uniform thickness was formed on the SiO2/Si substrate. Energy-dispersive X-ray analysis showed that the S/W ratio in the fabricated WS2 film was around 1.2 to 1.34, indicating certain deficiencies in the S atoms. These S vacancies induce localized states within the bandgap of pristine WS2, resulting in a higher conductivity in the exfoliated sample. The obtained thin film seems to be highly efficient in photoelectric conversion, with a responsivity of ~0.12 mA/W at 670 nm under zero bias voltage, with an intensity of 5.2 mW/cm2. Instead, at a bias of 2 V, it exhibits a responsivity of 12.74 mA/W and a detectivity of 1.17 × 1010 cm Hz1/2 W− 1 at 4.1 mW/cm2. The present 2D nanosheets exhibit high photon absorption in a wide range of spectra from the near infrared (IR) to near UV spectrum. 
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  2. Abstract

    The safety issue represents a long‐standing obstacle that retards large‐scale applications of high‐energy lithium batteries. Among different causes, thermal runaway is the most prominent one. To date, various approaches have been proposed to inhibit thermal runaway; however, they suffer from some intrinsic drawbacks, either being irreversible (one‐time protection), using volatile and flammable electrolytes, or delayed thermal protection (140–150 °C). Herein, this work exploits a non‐volatile, non‐flammable, and thermo‐reversible polymer/ionic liquid gel electrolyte as a built‐in safety switch, which provides highly precise and reversible thermal protection for lithium batteries. At high temperature, the gel electrolyte experiences phase separation and deposits polymer on the electrode surfaces/separators, which blocks Li+insertion reactions and thus prevents thermal runaway. When the temperature decreases, the gel electrolyte restores its original properties and battery performance resumes. Notably, the optimal protection effect is achieved at 110 °C, which is the critical temperature right before thermal runaway. More importantly, such a thermal‐protection process can repeat multiple times without compromising the battery performance, indicating extraordinary thermal reversibility. To the authors' knowledge, such a precise and reversible protection effect has never been reported in any electrolyte systems, and this work opens an exciting avenue for safe operation of high‐energy Li batteries.

     
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