The shuttling of soluble lithium polysulfides (LiPS) and the sluggish Li–S conversion kinetics are two main barriers toward the practical application of lithium–sulfur batteries (LSBs). Herein, we propose the addition of copper selenide nanoparticles at the cathode to trap LiPS and accelerate the Li–S reaction kinetics. Using both computational and experimental results, we demonstrate the crystal phase and concentration of copper vacancies to control the electronic structure of the copper selenide, its affinity toward LiPS chemisorption, and its electrical conductivity. The adjustment of the defect density also allows for tuning the electrochemically active sites for the catalytic conversion of polysulfide. The optimized S/Cu1.8Se cathode efficiently promotes and stabilizes the sulfur electrochemistry, thus improving significantly the LSB performance, including an outstanding cyclability over 1000 cycles at 3 C with a capacity fading rate of just 0.029% per cycle, a superb rate capability up to 5 C, and a high areal capacity of 6.07 mAh cm–2 under high sulfur loading. Overall, the present work proposes a crystal phase and defect engineering strategy toward fast and durable sulfur electrochemistry, demonstrating great potential in developing practical LSBs.
The direct, solid state, and reversible conversion between heat and electricity using thermoelectric devices finds numerous potential uses, especially around room temperature. However, the relatively high material processing cost limits their real applications. Silver selenide (Ag 2 Se) is one of the very few n-type thermoelectric (TE) materials for room-temperature applications. Herein, we report a room temperature, fast, and aqueous-phase synthesis approach to produce Ag 2 Se, which can be extended to other metal chalcogenides. These materials reach TE figures of merit (zT) of up to 0.76 at 380 K. To improve these values, bismuth sulfide (Bi 2 S 3 ) particles also prepared in an aqueous solution are incorporated into the Ag 2 Se matrix. In this way, a series of Ag 2 Se/Bi 2 S 3 composites with Bi 2 S 3 wt % of 0.5, 1.0, and 1.5 are prepared by solution blending and hot-press sintering. The presence of Bi 2 S 3 significantly improves the Seebeck coefficient and power factor while at the same time decreasing the thermal conductivity with no apparent drop in electrical conductivity. Thus, a maximum zT value of 0.96 is achieved in the composites with 1.0 wt % Bi 2 S 3 at 370 K. Furthermore, a high average zT value (zT ave ) of 0.93 in the 300−390 K range is demonstrated.
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