Lithium Lanthanum Titanium Oxides: A Fast Ionic Conductive Coating for Lithium-Ion Battery Cathodes

This work introduces Li–La–Ti–O (LLTO), which is a fast lithium-ion conductor, as an effective coating material for cathode materials used in rechargeable lithium-ion batteries. This fast Li-ion conductor is characterized by first-principles calculations showing low activation barrier for lithium diffusion at various different lithium concentrations. The morphology and the microstructure of the pristine electrode and coated electrode materials are characterized systematically, and we show clear evidence of the presence of the coating after electrochemical cycling. The coated electrodes show significantly improved rate capabilities and cycling performance, compared to the pristine electrodes. The possible reasons for such enhancements are explored experimentally using potentiostatic intermittent titration technique (PITT), electrochemical impedance spectroscopy (EIS). Because of the high lithium conductivity in the LLTO coating material, the chemical Li⁺ diffusion coefficient is one magnitude of order higher in the coated samples than that in the uncoated samples. In addition, the impedances of both interfacial charge transfer and Li⁺ transportation in the solid-electrolyte-interphase (SEI) layer are reduced up to 50% in the coated samples. Our findings provide significant insights into the role of coating regarding the improvements of electrochemical properties, as well as the potential use of solid electrolyte as an effective coating material

The Critical Role of Fluoroethylene Carbonate in the Gassing of Silicon Anodes for Lithium-Ion Batteries

The use of functionalized electrolytes is effective in mitigating the poor cycling stability of silicon (Si), which has long hindered the implementation of this promising high-capacity anode material in next-generation lithium-ion batteries. In this Letter, we present a comparative study of gaseous byproducts formed by decomposition of fluoroethylene carbonate (FEC)-containing and FEC-free electrolytes using differential electrochemical mass spectrometry and infrared spectroscopy, combined with long-term cycling data of half-cells (Si vs Li). The evolving gaseous species depend strongly on the type of electrolyte; the main products for the FEC-based electrolyte are H₂ and CO₂, while the FEC-free electrolyte shows predominantly H₂, C₂H₄, and CO. The characteristic shape of the evolution patterns suggests different reactivities of the various Li_<i>x</i>Si alloys, depending on the cell potential. The data acquired for long-term cycling confirm the benefit of using FEC as cosolvent in the electrolyte

Electrocatalytic Conversion of Carbon Dioxide to Methane and Methanol on Transition Metal Surfaces

Fuels and industrial chemicals that are conventionally derived from fossil resources could potentially be produced in a renewable, sustainable manner by an electrochemical process that operates at room temperature and atmospheric pressure, using only water, CO₂, and electricity as inputs. To enable this technology, improved catalysts must be developed. Herein, we report trends in the electrocatalytic conversion of CO₂ on a broad group of seven transition metal surfaces: Au, Ag, Zn, Cu, Ni, Pt, and Fe. Contrary to conventional knowledge in the field, all metals studied are capable of producing methane or methanol. We quantify reaction rates for these two products and describe catalyst activity and selectivity in the framework of CO binding energies for the different metals. While selectivity toward methane or methanol is low for most of these metals, the fact that they are all capable of producing these products, even at a low rate, is important new knowledge. This study reveals a richer surface chemistry for transition metals than previously known and provides new insights to guide the development of improved CO₂ conversion catalysts