Fabrication and Thermoelectric Properties of n‑Type CoSb_2.85Te_0.15 Using Selective Laser Melting

We report a nonequilibrium fabrication method of n-type CoSb_2.85Te_0.15 skutterudites using selective laser melting (SLM) technology. A powder of CoSb_2.85Te_0.15 was prepared by self-propagating high-temperature synthesis (SHS) and served as the raw material for the SLM process. The effect of SLM processing parameters such as the laser power and scanning speed on the quality of the forming CoSb_2.85Te_0.15 thin layers was systematically analyzed, and the optimal processing window for SLM was determined. A brief postannealing at 450 °C for 4 h, following the SLM process, has resulted in a phase-pure CoSb_2.85Te_0.15 bulk material deposited on a Ti substrate. The Seebeck coefficient of the annealed SLM prepared bulk material is close to that of the sample prepared by the traditional sintering method, and its maximum <i>ZT</i> value reached 0.56 at 823 K. Moreover, a Ti–Co–Sb ternary compound transition layer of about 70 μm in thickness was found at a dense interface between CoSb_2.85Te_0.15 and the Ti substrate. The contact resistivity was measured as 37.1 μΩcm². The results demonstrate that SLM, coupled with postannealing, can be used for fabrication of incongruently melting skutterudite compounds on heterogeneous substrates. This lays an important foundation for the follow-up research utilizing energy efficient SHS and SLM processes in rapid printing of thermoelectric modules

Facilitating the Operation of Lithium-Ion Cells with High-Nickel Layered Oxide Cathodes with a Small Dose of Aluminum

Layered oxide cathodes with a high Ni content of >0.6 are promising for high-energy-density lithium-ion batteries. However, parasitic electrolyte oxidation of the charged cathode and mechanical degradation arising from phase transitions significantly deteriorate the cell performance and cycle life as the Ni content increases. We demonstrate here a significantly prolonged cycle life with superior cell performance by substituting a small-dose of Al (2 mol %) for Ni in LiNi_0.92Co_0.06Al_0.02O₂; the capacity retention after operating a full cell fabricated with graphite anode for 1000 cycles increases from 47% to 83% on going from the Al-free LiNi_0.94Co_0.06O₂ to the Al-doped LiNi_0.92Co_0.06Al_0.02O₂ cathode. Through in situ X-ray diffraction, we provide the operando evidence that the Al-doping tunes the H2–H3 phase transition process from a two-phase reaction to a quasi-monophase reaction, minimizing the mechanical degradation. Furthermore, secondary-ion mass spectrometry reveals considerably suppressed transition-metal dissolution with Al-doping, effectively preventing sustained parasitic reactions and active Li trapping due to chemical crossover on graphite anodes. This work offers a viable approach for adopting high-Ni cathodes in lithium-ion batteries

Field-Effect Tuned Adsorption Dynamics of VSe₂ Nanosheets for Enhanced Hydrogen Evolution Reaction

Transition metal dichalcogenides, such as MoS₂ and VSe₂ have emerged as promising catalysts for the hydrogen evolution reaction (HER). Substantial work has been devoted to optimizing the catalytic performance by constructing materials with specific phases and morphologies. However, the optimization of adsorption/desorption process in HER is rare. Herein, we concentrate on tuning the dynamics of the adsorption process in HER by applying a back gate voltage to the pristine VSe₂ nanosheet. The back gate voltage induces the redistribution of the ions at the electrolyte–VSe₂ nanosheet interface, which realizes the enhanced electron transport process and facilitates the rate-limiting step (discharge process) under HER conditions. A considerable low onset overpotential of 70 mV is achieved in VSe₂ nanosheets without any chemical treatment. Such unexpected improvement is attributed to the field tuned adsorption-dynamics of VSe₂ nanosheet, which is demonstrated by the greatly optimized charge transfer resistance (from 1.03 to 0.15 MΩ) and time constant of the adsorption process (from 2.5 × 10^–3 to 5.0 × 10^–4 s). Our results demonstrate enhanced catalysis performance in the VSe₂ nanosheet by tuning the adsorption dynamics with a back gate, which provides new directions for improving the catalytic activity of non-noble materials