• Energy Research
• 7. Clean energy close

Neutron and electron spectroscopy reveal diffusion behavior of individual ions in lithium garnets, paving the way towards high-performance aqueous lithium batteries.

AbstractThe electroreduction of C1 feedgas to high-energy-density fuels provides an attractive avenue to the storage of renewable electricity. Much progress has been made to improve selectivity to C1 and C2 products, however, the selectivity to desirable high-energy-density C3 products remains relatively low. We reason that C3 electrosynthesis relies on a higher-order reaction pathway that requires the formation of multiple carbon-carbon (C-C) bonds, and thus pursue a strategy explicitly designed to couple C2 with C1 intermediates. We develop an approach wherein neighboring copper atoms having distinct electronic structures interact with two adsorbates to catalyze an asymmetric reaction. We achieve a record n-propanol Faradaic efficiency (FE) of (33 ± 1)% with a conversion rate of (4.5 ± 0.1) mA cm−2, and a record n-propanol cathodic energy conversion efficiency (EEcathodic half-cell) of 21%. The FE and EEcathodic half-cell represent a 1.3× improvement relative to previously-published CO-to-n-propanol electroreduction reports.

The carbon dioxide electroreduction reaction (CO2RR) provides ways to produce ethanol but its Faradaic efficiency could be further improved, especially in CO2RR studies reported at a total current density exceeding 10 mA cm−2. Here we report a class of catalysts that achieve an ethanol Faradaic efficiency of (52 ± 1)% and an ethanol cathodic energy efficiency of 31%. We exploit the fact that suppression of the deoxygenation of the intermediate HOCCH* to ethylene promotes ethanol production, and hence that confinement using capping layers having strong electron-donating ability on active catalysts promotes C–C coupling and increases the reaction energy of HOCCH* deoxygenation. Thus, we have developed an electrocatalyst with confined reaction volume by coating Cu catalysts with nitrogen-doped carbon. Spectroscopy suggests that the strong electron-donating ability and confinement of the nitrogen-doped carbon layers leads to the observed pronounced selectivity towards ethanol. The electroreduction of CO2 to ethanol could enable the clean production of fuels using renewable power. This study shows how confinement effects from nitrogen-doped carbon layers on copper catalysts enable selective ethanol production from CO2 with a Faradaic efficiency of up to 52%.

High voltage cathode materials Li-excess layered oxide compounds Li[NixLi1/3−2x/3Mn2/3−x/3]O2 (0 < x < 1/2) are investigated in a joint study combining both computational and experimental methods. The bulk and surface structures of pristine and cycled samples of Li[Ni1/5Li1/5Mn3/5]O2 are characterized by synchrotron X-Ray diffraction together with aberration corrected Scanning Transmission Electron Microscopy (a-S/TEM). Electron Energy Loss Spectroscopy (EELS) is carried out to investigate the surface changes of the samples before/after electrochemical cycling. Combining first principles computational investigation with our experimental observations, a detailed lithium de-intercalation mechanism is proposed for this family of Li-excess layered oxides. The most striking characteristics in these high voltage high energy density cathode materials are 1) formation of tetrahedral lithium ions at voltage less than 4.45 V and 2) the transition metal (TM) ions migration leading to phase transformation on the surface of the materials. We show clear evidence of a new spinel-like solid phase formed on the surface of the electrode materials after high-voltage cycling. It is proposed that such surface phase transformation is one of the factors contributing to the first cycle irreversible capacity and the main reason for the intrinsic poor rate capability of these materials.

Li-ion-conducting solid electrolytes are the potential solution to the severe safety issues that occur with conventional batteries based on solvent-based electrolytes. The ionic conductivity of solid electrolytes is in general too low, however, due to a high grain-boundary (GB) resistance. A thorough understanding of the ionic transport mechanism at GBs in these materials is critical for a revolutionary development of next-generation Li batteries. Herein we present the first atomic-scale study to reveal the origin of the large GB resistance; (Li3xLa2/3−x)TiO3 was chosen as a prototype material to demonstrate the concept. A strikingly severe structural and chemical deviation of about 2–3 unit cells thick was revealed at the grain boundaries. Instead of preserving the ABO3 perovskite framework, such GBs were shown to consist of a binary Ti–O compound, which prohibits the abundance and transport of the charge carrier Li+. This observation has led to a potential strategy for tailoring the grain boundary structures. This study points out, for the first time, the importance of the atomic-scale grain-boundary modification to the macroscopic Li+ conductivity. Such a discovery paves the way for the search and design of solid electrolytes with superior performance.

A TiNb2O7 material with a nanoporous structure was prepared by a facile approach and can be used as an anode with excellent rate and cycling performance for long-life stationary lithium-ion batteries.

Design of active and stable Pt-based nanoscale electrocatalysts for the oxygen reduction reaction (ORR).