Interfacial properties of alloy anodes in combination with room temperature ionic liquid electrolytes: A review based on Li secondary batteries

Activation Energy of Ion Desorption at Ionic Liquid/Pt Electrode Interfaces: A Sum-Frequency Generation Vibrational Spectroscopic Study

Electrolyte/electrode interfaces of room-temperature ionic liquids (RTILs) exhibit hysteretic responses to different applied potentials owing to the differences in the ion adsorption/desorption processes; the ion desorption requires excess potential, which reflects the activation energy of ion desorption. Thus far, the contributions of the ion adsorption energy and the activation barrier for ion desorption toward the ion-dependent excess potential have not been quantified. Herein, we report on our infrared-visible sum-frequency generation vibrational spectroscopy study of the hysteretic responses of the anion adsorption/desorption at Pt electrode interfaces using neat, binary, and diluted RTILs composed of 1-butyl-3-methylimidazolium cations ([C4mim]+) and bis(trifluoromethanesulfonyl)amide ([TFSA]-) and trifluoromethanesulfonate ([OTf]-) anions. Experimental results are compared to the theoretical calculations for the electric double layer model. The hysteretic response of the RTIL/Pt interface derives predominantly from the activation energy of anion desorption, which causes the negative excess potential required for anion desorption. A comparison of the anion adsorption/desorption behaviors of neat RTILs with those of binary and diluted RTILs reveals that the large activation energy of anion desorption at the neat RTIL/Pt interface originates largely from the activation barrier for restructuring ionic layering in the diffuse layer.

Microscale Silicon-Based Anodes: Fundamental Understanding and Industrial Prospects for Practical High-Energy Lithium-Ion Batteries

To accelerate the commercial implementation of high-energy batteries, recent research thrusts have turned to the practicality of Si-based electrodes. Although numerous nanostructured Si-based materials with exceptional performance have been reported in the past 20 years, the practical development of high-energy Si-based batteries has been beset by the bias between industrial application with gravimetrical energy shortages and scientific research with volumetric limits. In this context, the microscale design of Si-based anodes with densified microstructure has been deemed as an impactful solution to tackle these critical issues. However, their large-scale application is plagued by inadequate cycling stability. In this review, we present the challenges in Si-based materials design and draw a realistic picture regarding practical electrode engineering. Critical appraisals of recent advances in microscale design of stable Si-based materials are presented, including interfacial tailoring of Si microscale electrode, surface modification of SiO_x microscale electrode, and structural engineering of hierarchical microscale electrode. Thereafter, other practical metrics beyond active material are also explored, such as robust binder design, electrolyte exploration, prelithiation technology, and thick-electrode engineering. Finally, we provide a roadmap starting with material design and ending with the remaining challenges and integrated improvement strategies toward Si-based full cells.

Material and Interfacial Modification toward a Stable Room-Temperature Solid-State Na-S Battery

Room-temperature solid-state sodium batteries have the remarkable potential to simultaneously achieve high safety, high energy density, and low cost. However, their current performance is far below expectations. Through material and interfacial modification based on Na₃PS₄ solid electrolytes, progress is made toward stable room-temperature solid-state sodium-sulfur (Na-S) batteries. First, the ionic liquid N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (Pyr₁₄FSI) is employed to modify the anode/electrolyte interface. An overpotential of 0.55 V after 900 h of a symmetrical battery indicates enhanced interfacial stability. A stable in situ solid electrolyte interphase layer is formed at the interface of NaSn alloy and Na₃PS₄, proved by X-ray photoelectron spectroscopy measurements. Furthermore, selenium-doped sulfurized polyacrylonitrile (Se_0.05S_0.95@pPAN) is used to boost the ionic and electronic conductivities of the sulfur cathode. As a result, the Na-S battery using a Se_0.05S_0.95@pPAN cathode and the interfacial modification delivers stable cycle performance and enhanced rate capability.