Sustainable Mesoporous Carbons as Storage and Controlled-Delivery Media for Functional Molecules

Here, we report the synthesis of surfactant-templated mesoporous carbons from lignin, which is a biomass-derived polymeric precursor, and their potential use as a controlled-release medium for functional molecules such as pharmaceuticals. To the best of our knowledge, this is the first report on the use of lignin for chemical-activation-free synthesis of functional mesoporous carbon. The synthesized carbons possess the pore widths within the range of 2.5–12.0 nm. In this series of mesoporous carbons, our best result demonstrates a Brunauer–Emmett–Teller (BET) surface area of 418 m²/g and a mesopore volume of 0.34 cm³/g, which is twice the micropore volume in this carbon. Because of the dominant mesoporosity, this engineered carbon demonstrates adsorption and controlled release of a representative pharmaceutical drug, captopril, in simulated gastric fluid. Large-scale utilization of these sustainable mesoporous carbons in applications involving adsorption, transport, and controlled release of functional molecules is desired for industrial processes that yield lignin as a coproduct

Unraveling the Voltage-Fade Mechanism in High-Energy-Density Lithium-Ion Batteries: Origin of the Tetrahedral Cations for Spinel Conversion

High-voltage layered lithium- and manganese-rich (LMR) oxides have the potential to dramatically enhance the energy density of current Li-ion energy storage systems. However, these materials are currently not used commonly; one reason is their inability to maintain a consistent voltage profile (voltage fade) during electrochemical cycling. This report rationalizes the cause of this voltage fade by providing evidence of layered to spinel (LS) structural evolution pathways in the host Li_1.2Mn_0.55Ni_0.15Co_0.1O₂ oxide. By employing neutron powder diffraction, we show that LS structural rearrangement in the LMR oxide occurs through a tetrahedral cation intermediate via the following: (i) diffusion of lithium atoms from octahedral to tetrahedral sites of the lithium layer [(Li_Lioct → Li_Litet] which is followed by the dispersal of the lithium ions from the adjacent octahedral site of the metal layer to the tetrahedral sites of lithium layer [Li_TMoct → Li_Litet]; (ii) migration of Mn from the octahedral sites of the transition-metal layer to the “permanent” octahedral site of lithium layer via tetrahedral site of lithium layer [Mn_TMoct → Mn_Litet → Mn_Lioct)]. These findings open the door to potential routes to mitigate this “atomic restructuring” in the high-voltage LMR composite oxide by manipulating their composition/structure for practical use in high-energy-density lithium-ion batteries

Neutron Diffraction and Magnetic Susceptibility Studies on a High-Voltage Li_1.2Mn_0.55Ni_0.15Co_0.10O₂ Lithium Ion Battery Cathode: Insight into the Crystal Structure

Lithium- and manganese-rich oxides undergo structural transformation and/or atomic rearrangements during the delithiation/lithiation process and ultimately suffer from several issues such as first cycle irreversible capacity and voltage fade. In order to understand the mechanism of these issues, perception of a detailed crystal structure of pristine material is obviously demanding. In this study, combined powder neutron diffraction (ND) and temperature-dependent magnetic susceptibility techniques were employed to investigate the structure of a pristine lithium- and manganese-rich Li_1.2Mn_0.55Ni_0.15Co_0.10O₂ cathode oxide. Rietveld refinement on the experimental ND pattern yields good fits by considering either Li₂MO₃ (M = Co, Mn, Ni) type monoclinic (<i>C2/m</i> space group) phase with 1% of Ni residing in the 4h lithium site or a composite structure consisting of 50% of Li₂MnO₃ type monoclinic (<i>C2/m</i> space group) and 50% LiMO₂ (M = Co, Mn, Ni) type trigonal (<i>R</i>3̅<i>m</i> space group) structure. In the composite structure, 3% Li/Ni site exchange in the trigonal phase is also proposed. Further, temperature-dependent dc magnetic susceptibility shows Curie–Weiss paramagnetic behavior at <i>T</i> ≥ 100 K, and no ordering/deviation of the field cooling (FC) curve in the temperature range 2–320 K indicates the random distribution of metal ions in the transition metal (TM) layer in the trigonal phase. Bifurcation of the zero-field cooling (ZFC) curve from the FC curve showing a magnetic ordering at <i>T</i>_N<i> ∼</i> 50 K reveals the presence of cation ordering in the TM layers arising from a distinct Li₂MnO₃-like phase. These results suggest that the lithium- and manganese-rich oxide with a composition Li_1.2Mn_0.55Ni_0.15Co_0.10O₂ is more likely a composite of monoclinic and trigonal phases. The report also highlights the unique materials diagnostic capability of combined ND and magnetic susceptibility techniques to obtain detailed structural information of complex oxide systems

Anomalous High Ionic Conductivity of Nanoporous β‑Li₃PS₄

Lithium-ion-conducting solid electrolytes hold promise for enabling high-energy battery chemistries and circumventing safety issues of conventional lithium batteries. Achieving the combination of high ionic conductivity and a broad electrochemical window in solid electrolytes is a grand challenge for the synthesis of battery materials. Herein we show an enhancement of the room-temperature lithium-ion conductivity by 3 orders of magnitude through the creation of nanostructured Li₃PS₄. This material has a wide electrochemical window (5 V) and superior chemical stability against lithium metal. The nanoporous structure of Li₃PS₄ reconciles two vital effects that enhance the ionic conductivity: (1) the reduction of the dimensions to a nanometer-sized framework stabilizes the high-conduction β phase that occurs at elevated temperatures, and (2) the high surface-to-bulk ratio of nanoporous β-Li₃PS₄ promotes surface conduction. Manipulating the ionic conductivity of solid electrolytes has far-reaching implications for materials design and synthesis in a broad range of applications, including batteries, fuel cells, sensors, photovoltaic systems, and so forth