RESUMEN
The instability of Nickel (Ni)-rich cathodes at high voltage is a critical bottleneck toward developing superior lithium-ion batteries. This instability is driven by cathode-electrolyte side reactions, causing rapid degradation, and compromising the overall cycle life. In this study, a protective coating using dispersed "magnetite (FeO.Fe2O3)" nanoparticles is used to uniformly decorate the surface of LiNi0.8Co0.1Mn0.1O2 (NMC 811) microparticles. The modified cathode delivers significant improvement in electrochemical performance at high voltage (≈4.6 V) by suppressing deleterious electrode-electrolyte interactions. A notably higher cycle stability, rate performance, and overall energy density is realized for the coated cathode in a conventional liquid electrolyte battery. When deployed in pellet-stacked solid-state cells with Li6PS5Cl as the electrolyte, the magnetite-coated NMC 811 showed strikingly superior cycling stability than its uncoated counterpart, proving the versatility of the chemistry. The facile surfactant-assisted coating process developed in this work, in conjunction with the affordability, abundance, and nontoxic nature of magnetite makes this a promising approach to realize commercially viable high voltage Ni-rich cathodes that exhibit stable performance in liquid as well as solid-state lithium-ion batteries.
RESUMEN
The non-toxic and stable chalcogenide perovskite BaZrS3 fulfills many key optoelectronic properties for a high-efficiency photovoltaic material. It has been shown to possess a direct band gap with a large absorption coefficient and good carrier mobility values. With a reported band gap of 1.7-1.8 eV, BaZrS3 is a good candidate for tandem solar cell materials; however, its band gap is significantly larger than the optimal value for a high-efficiency single-junction solar cell (â¼1.3 eV, Shockley-Queisser limit)âthus doping is required to lower the band gap. By combining first-principles calculations and machine learning algorithms, we are able to identify and predict the best dopants for the BaZrS3 perovskites for potential future photovoltaic devices with a band gap within the Shockley-Queisser limit. It is found that the Ca dopant at the Ba site or Ti dopant at the Zr site is the best candidate dopant. Based on this information, we report for the first time partial doping at the Ba site in BaZrS3 with Ca (i.e., Ba1-xCaxZrS3) and compare its photoluminescence with Ti-doped perovskites [i.e., Ba(Zr1-xTix)S3]. Synthesized (Ba,Ca)ZrS3 perovskites show a reduction in the band gap from â¼1.75 to â¼1.26 eV with <2 atom % Ca doping. Our results indicate that for the purpose of band gap tuning for photovoltaic applications, Ca-doping at the Ba-site is superior to Ti-doping at the Zr-site reported previously.
RESUMEN
Looming concerns regarding scarcity, high prices, and safety threaten the long-term use of lithium in energy storage devices. Calcium has been explored in batteries because of its abundance and low cost, but the larger size and higher charge density of calcium ions relative to lithium impairs diffusion kinetics and cyclic stability. In this work, an aqueous calcium-ion battery is demonstrated using orthorhombic, trigonal, and tetragonal polymorphs of molybdenum vanadium oxide (MoVO) as a host for calcium ions. Orthorhombic and trigonal MoVOs outperform the tetragonal structure because large hexagonal and heptagonal tunnels are ubiquitous in such crystals, providing facile pathways for calcium-ion diffusion. For trigonal MoVO, a specific capacity of â¼203 mAh g-1 was obtained at 0.2C and at a 100 times faster rate of 20C, an â¼60 mAh g-1 capacity was achieved. The open-tunnel trigonal and orthorhombic polymorphs also promoted cyclic stability and reversibility. A review of the literature indicates that MoVO provides one of the best performances reported to date for the storage of calcium ions.
